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ΜΕΤΑΠΤΥΧΙ

ΟΟΤΤΗΗΤΤΑΑΣΣ ΣΣ

ΟΟΡΡΑΑΜΜΙΙΚΚ

ΔΔΙΙΠΠΛΛΩΩΜ

ΝΝιιώώΑρ.

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ΙΙΣΣΣΤΤΤΗΗΗΜΜΜΙΙΙΟΟΟΟΟΟ

ΤΡΙΚΗΣ – ΤΜ

ΑΤΙΚΟ ΠΡΟΓΡ

ΙΑΚΩΝ ΣΠΟΥ

ΣΣΥΥΣΣΤΤΗΗΜΜΑΑ

ΗΣΗΣ ΑΑΚΚΤΤΙΙΝΝ

ΜΜΑΑΤΤΙΙΚΚΗΗ ΕΕ

ττοουυ

ώώττηη ΔΔηημμήή. Μητρώου: 1

ΠΠΑΑΤΤΡΡΩΩΝΝ

ΠΠΑΑΤΤΡΡΑΑ

ΕΕΚΚΕΕΜΜΒΒΡΡΙΙΟΟΣΣ,, 2200

ΠΠΠΑΑΑΤΤΤΡΡΡΩΩΩΝΝΝΝ

ΜΗΜΑ ΦΥΣΙΚΚΗΣ ΡΑΜΜΑ

ΥΔΩΝ ΣΤΗΝ ΙΑΤΡΙΚΗ ΦΥΥΣΙΚΗ

ΑΤΤΩΩΝΝ ΟΟΑ ΔΔ

ΝΝΟΟΓΓΡΡΑΑΦΦ

ΕΕΡΡΓΓΑΑΣΣΙΙΑΑ

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ACKNOWLEDGMENTS

I would like to thank Professor George Panayiotakis for his inspiring, encouraging and

helpful guidance and consistent supervision on my work, as also for the extensive and

sincere discussions on several subjects that we shared.

I would also like give special thanks to Medical Radiation Physicist Harry Delis for his

enormous and direct help concerning various questions and clarifications aroused on my

research as well as on the experimental procedures.

Last but not least, I would like to thank all friends, closed ones and colleagues who

showed a remarkably inexhaustible, encouraging ‐yet hopefully not inexplicable‐

patience concerning the making of this work.

iii

PREFACE

Over the last decades, medical x rays have remarkably expanded their necessity on

medical diagnosis, treatment planning and evaluation of therapy. In this way, the

parallel ongoing development as well as the evolution of the x ray techniques has

brought a vast range of potential usage, which needs to be fairly acknowledged for the

optimization of each technique and the overall control of the radiation dosage, not to

mention the permanently questioned necessity and high rates of the examinations.

Dental radiography represents the most frequent diagnostic x ray examination

undertaken in the industrialized countries of the world. On this basis, the relatively low

dosage of these techniques can not underestimate the questions of radioprotection

fields, as for example the overall dosage in each country from these techniques is more

than negligible.

Panoramic radiography is a simplified dental extraoral procedure which depicts the

entire maxillomandibular region on a single film. The development of the principles of

dental panoramic radiology represented a major innovation in dental imaging. Prior to

this, dental radiographic examinations were limited to intraoral and oblique lateral

projections of the jaws taken using a dental x ray set. For the first time practitioners

were able to produce an image of both jaws and their respective dentitions on a single

radiographic film by a quick and relatively simple procedure.

The simplicity of operation, the broadened scope of examination, the ability to project

anatomic structures in their normal relationship with reduced superimposition of

intervening parts, and the low radiation dosage are reasons for its widely growing

popularity. The latter has raised the necessity of the formation of a regulatory basis in

each country, according to the demographic and practitioners standards, which will

provide a safe and proper quality assurance guide, allowing each practitioner to

optimize the technique, both in terms of image quality and patient dosimetry, according

to the subjective grounds of every laboratory, rather than restricting the practice into a

single and solid mode.

Quality Control (QC) protocols, Diagnostic Reference Levels (DRLs) and guidance

programs for proper usage of the panoramic unit as well as the processing procedures

are some of the fields that need to researched and well established.

In Greece, where the number of both panoramic units and examinations follow a

remarkably yet undefined increasing curve during the last two decades, there has been

v

initialized a researching and scientific debate about these fields although it is still in a

primary stage.

The following thesis, taking into consideration the difficulties and the complexity of this

technique, as well as the questions and problems that rise upon its general practice in

Greek laboratories, and trying to provide a more aggregate view of panoramic imaging,

focuses on the QC of panoramic radiography, including the determination of DRLs in this

technique, with a respective presentation of the principles of function and the necessary

radioprotection information.

vi

viii

Contents

SECTION I

GENERAL PART

CHAPTER 1 : The included anatomical structures on the panoramic radiograph

Introduction 3 The Skull 3 The Mandible 4 The Maxilla (Upper Jaw) 5 The Temperomandibular Joint 5 The Foramina 6 The Salivary Glands 7The Cervical Vertebrae 8

General Overview of the Oral, Neck and Lower Face Anatomy 8The Tongue 9

Oral Anatomy Elements 9The Tooth 11

Tooth Development 12

CHAPTER 2 : Panoramic Radiography: a clinical overview

Introduction 19Diagnostic Regions in PR 19The Normal Panoramic Radiograph 21

CHAPTER 3 : Panoramic Radiography: principles of function

Introduction 30Broad Beam Linear Tomography 31Slit or Narrow Beam Linear Tomography 31Narrow Beam Rotational Tomography 32Dental Panoramic Tomography 33

Focal Trough 35 Formation of the Image Layer 38 Geometric Distortion 41

Screen Film and Intensifying Screens 43The Screen Film 43Intensifying Screens 45Digital Panoramic Tomography 48

ix

Solid‐state systems using CCD 50 Storage Phosphor Plates Technology 53 Interoperability 55Radiation Dosage 56

Comparison Between Film and Digital PR 56Equipment 58Patient Positioning 61Field Limitation Techniques 62

CHAPTER 4: Radiation Effects, Doses and Protection concerning Quality Controlling of panoramic radiography

Introduction 65Sources of Radiation 66Classification of Biological Effects 67

Somatic Deterministic Effects 67 Somatic Stochastic Effects 67 Genetic Stochastic Effects 68

Harmful Effects Important in Dental Radiology 69Estimating the Dose and Risk of PR 69Main Methods of Monitoring and Measuring Radiation Dose 73

Film Badges 73TLDs 74Ionization Chambers 75

Measurements using Phantoms 75Patient Dosimetry 75List of Equipment 76

Methods 76 Worksheets 83

Dose Area Product 86Diagnostic Reference Levels (DRLs) deriving from DAP measurements 87Dose Width Product 88DAP and Effective Dose 89

CHAPTER 5: Quality Control Protocols – Codes of Practice ‐ Legislation

Greek Atomic Energy Commission Protocol of Periodical Quality Control Checks on Orthopantograph

92

Requirements for Dental Panoramic and Cephalometric Examinations, by GAEC 93

Conference of Radiation Control Program Directors, Inc Quality Control Recommendations for Diagnostic Radiography

94

European Commission – Radiation Protection 136 European Guidelines Radiation Protection in Dental Radiology, 2004

95

International Atomic Energy Agency – Dosimetry in Diagnostic Radiology: An International Code of Practice

96

x

Health Canada – Radiation Protection in Dentistry, Recommended Safety Procedures for the Use of Dental x ray Equipment

96

Care Quality Commission – The Ionizing Radiation (Medical Exposure) Regulations 97

Greek Ministry of Health, Greek Regulations for Radiation Protection, 2001. 97

SECTION II

EXPERIMENTAL PART

CHAPTER 6:

Calculation of the Effective Dose (E), Using the DRLs of Tierris et al. (2004)

101

CHAPTER 7: Quality Control of a Panoramic Unit

A.1 LABORATORY DESCRIPTION – EQUIPMENT RECORDA.1.1 Equipment Description 104 A.1.2 Ventilation – Air Condition ‐ Illumination 106

A.2 CONTROLS A.2.1 General Apparatus Controls 107

A.2.1.1 Inspectional Control of the Unit Components 107A.2.1.3 Presence of Technical Manuals and Log Book 107

A.2.2 Radioprotection Control 108A.2.2.1 Spatial Characterization – Chamber Signage 108A.2.2.2 Verification of Radioprotection Report – Shield Control 108A.2.2.3 Record and Control of Physical Condition of Radioprotection Apparatus

109

A.2.2.4 Tube Head Escape 109A.2.3 Beam Geometry Control 110

A.2.3.1 Conjunction of Radiation Field with the Alignment Slit of the Digital Detector

110

A.2.3.2 Measurement of Minimum Distance Focus‐Examinee 110A.2.3.3 FFD Control 110

A.2.4 Beam Quality Control 111A.2.4.1 Accuracy of High Voltage Values 111A.2.4.2 Repeatability of High Voltage Values 112A.2.4.3 Half Value Layer (HVL) of the beam – Tube Total Filtering 113

A.2.5 Beam Quantity Control 114

xi

A.2.5.1 Timer Accuracy 114A.2.5.2 Timer Repeatability 115A.2.5.3 Tube Supply Linearity and Repeatability 115

A.2.6 Automatic Exposure Selection System 116A.2.7 Typical Patient Doses 118A.2.8 Image Quality Control 118

REFERENCES 120

Appendix I: The Diagnostic Value of the Panoramic Radiograph

The Popularity of Panoramic Imaging 128 The Quality of Panoramic Images 129Technical and Processing Faults Affecting Image Quality 130Film Fault Frequency within Panoramic Radiographs taken in General Dental Practice

134

The Questionable Necessity of the Panoramic Radiograph 138The Panoramic X‐ray Equipment and the Operating Personnel 142

xiii

Lists of Figures

CHAPTER 1 Figure 1: http://www.3dmouth.org/4/4_1.cfm

Figure 2: http://www.3dmouth.org/4/4_2_1.cfm




Figure 6: http://www.3dmouth.org/4/4_3.cfm

Figure 7: http://www.en.wikipedia.org/wiki/File:Illu_vertebral_column.jpg

Figure 8: http://www.doctorspiller.com/oral%20anatomy.htm

Figure 9: http://www.med.mun.ca/anatomys/head/head.htm

Figure 10: http://www.doctorspiller.com/oral%20anatomy.htm

Figure 11: http://www6.ufrgs.br/favet/imunovet/molecular_immunology/tooth1.jpg


Figure 13: http://dentdoctor.tripod.com/Oral_Anatomy/index2.html



Figure 16: http://www.nytimes.com/imagepages/2007/08/01/health/adam/9445Dentalanatomy.html


Figure 18: Pasler A Friedrich. Color Atlas of Dental Medicine, p. 62 – Radiology, Thieme, 1993

Figure 19: http://en.wikipedia.org/wiki/File:Teeth_diagram.png


Figure 21: Pasler A Friedrich, Visser Heiko. Pocket Atlas of Dental Radiology, Panoramic Radiography, Tooth and Jaw Development as Depicted in Panoramic Radiographs, page 37, Thieme, 2007.



http://www.3dmouth.org/4/4_2_2.cfm



http://www.3dmouth.org/4/4_3.cfm

http://www.en.wikipedia.org/wiki/File:Illu_vertebral_column.jpg

http://www.doctorspiller.com/oral%20anatomy.htm

http://www.doctorspiller.com/oral%20anatomy.htm

http://www6.ufrgs.br/favet/imunovet/molecular_immunology/tooth1.jpg


http://dentdoctor.tripod.com/Oral_Anatomy/index2.html




http://en.wikipedia.org/wiki/File:Teeth_diagram.png


xiv



Figure 26: http://media‐2.web.britannica.com/eb‐media/91/74891‐004‐345232AC.jpg

CHAPTER 2





Figure 5: Farman G Allan. Panoramic Radiology – Seminars on Maxillofacial Imaging and Interpretation, Chapter 1, p. 4, Springer, 2007


Figure 7: William S. Moore. Kodak Successful Panoramic Radiography, p.2

Figure 8: Murray Diane, Whyte Andy. Dental Panoramic Tomography: What the General Radiologist Needs to Know. Clinical Radiology 57: 1‐7, 2002.

Figure 9: Murray Diane, Whyte Andy. Dental Panoramic Tomography: What the General Radiologist Needs to Know. Clinical Radiology 57: 1‐7, 2002.

CHAPTER 3 Figure 1: Whaites E. Essentials of Dental Radiography and Radiology, Chapter 15, p.

162. 2nd ed. (Edinburgh: Churchill Livingstone) 1996. Figure 2: Whaites E. Essentials of Dental Radiography and Radiology, Chapter 15, p.




164. 2nd ed. (Edinburgh: Churchill Livingstone) 1996. Figure 6: White S C, Pharoah M J. Oral Radiology: Principles and Interpretation,

Chapter 11, p. 208, 4th ed. (St.Louis: Mosby Inc.) 2000. Figure 7: Whaites, E. Essentials of Dental Radiography and Radiology, Chapter 15, p.

165. 2nd ed. (Edinburgh: Churchill Livingstone) 1996. Figure 8: X ray Phantoms, Panoramic Dental Test Object, TO PAN, Leeds Test Objects

xv

Figure 9: X ray Phantoms, Panoramic Dental Test Object, TO PAN, Leeds Test Objects

Figure 10: William S. Moore. Successful Panoramic Radiography, Kodak Dental Radiography Series.

Figure 11: http://www.kodak.com/US/plugins/acrobat/en/motion/support/h1/H1_23‐27.pdf

Figure 12: http://www.medcyclopaedia.com/library/topics/volume_i/f/film_screen_radiography.aspx

Figure 13: http://www.medcyclopaedia.com/upload/medcyc/volumes/volume_i/dintensifying_screen_fig1.jpg

Figure 14: Farman G Allan. Panoramic Radiology – Seminars on Maxillofacial Imaging and Interpretation, Chapter 3, Springer, 2007








Figure 22: Whaites E. Essentials of Dental Radiography and Radiology, Chapter 15, p. 168. 2nd ed. (Edinburgh: Churchill Livingstone) 1996.




CHAPTER 4 Figure 1: White S C, Pharoah M J. Oral Radiology: Principles and Interpretation,

Chapter 3, p. 44, 4th ed. (St. Louis: Mosby Inc.) 2000. Figure 2: Whaites E. Essentials of Dental Radiography and Radiology, Chapter 4, p.



64. 2nd ed. (Edinburgh: Churchill Livingstone) 1996.

Figure 5: International Atomic Energy Agency. Dosimetry in Diagnostic Radiology: An International Code of Practice (Technical Reports Series No. 457). Vienna, 2007

Figure 6: Williams JR, Montgomery A. Measurement of dose in panoramic dental radiology. Br J Radiol;73(873):1002–6, 2000.

http://www.medcyclopaedia.com/upload/medcyc/volumes/volume_i/dintensifying_screen_fig1.jpg

http://www.medcyclopaedia.com/upload/medcyc/volumes/volume_i/dintensifying_screen_fig1.jpg

xvi

Figure 7: http://www.gehealthcare.com/usen/xr/edu/products/dose.html

Figure 8: http://www.e‐radiography.net/radtech/d/Dose_ge/dose.htm

APPENDIX I

Figure 1‐6: Akarslan ZZ, Erten H, Güngör K, et. al. Common Errors on Panoramic Radiographs Taken in a Dental School. J Contemporary Dental Practice;(4)2:024‐034, May 2003

SECTION I

GENERAL PART

1

CCHAPTEER 1

THE INCLUUDED ANNATOMIICAL STRUCTURRES

ON THHE PANOORAMIC RADIOGGRAPH

INNTRODUCTION

On

as

Du

co

st

in

n this sectio

s all the add

ue to this pr

onsists a ba

ructures, the

terpretation

n, a short an

ditional struc

roject’s goal

sic and very

eir surround

n of the pano

natomical re

ctures that a

s, which are

y brief anat

ding tissues a

oramic radiog

eference of t

appear or m

e not such o

tomical refe

and their rel

graphy and t

the dental re

ay appear in

of a pure me

erence. The

ations is an

the discussio

egion is pres

n a panoram

edical interes

knowledge

essential too

on of its qual

sented, as w

mic radiograp

st, this secti

of the den

ol for a prop

ity control.

well

ph.

on

tal

per

THHE SKULL

Th

th

he skull is a h

he human sp

hollow and r

pine providin

F

rigid structur

ng a protectiv

Figure 1: The Hu

3

re made of b

ve shell to t

uman Skull

bone tissue.

he brain and

all the he

enabling

head (che

expressio

The skull

1) The cra

is the top

2) The fac

of the fa

region.

It is attached

d the eyes. U

ead muscles

all the fun

ewing, air cir

ns etc.).

d on the top

Upon the sku

s are attache

nctions of t

rculation, fac

of

ull,

ed,

the

cial

is divided intto two parts:

anial part o

part that co

r “cranium”

overs the bra

”. It

ain.

cial part whi

acial bones

ich is consist

at the fro

ted

ont

THHE MANDIBBLE (LOWERR JAW)

Th

an

ea

th

he lower jaw

nd it stretche

ar. It is joine

he “temporo

w has its own

es from one

ed to the upp

‐mandibular

n separate b

ear, down to

per part of t

r joints – TM

bone which is

o the chin ar

the head aro

MJs”.

s called “the

ea and then

ound the ear

e mandible”.

back up aga

r region by t

It is U‐shap

ain to the oth

two jaw join

ped

her

nts,

Thhe mandible is divided into the followwing parts:

The b

‐

of th

suppo

ody f the m

the middle

he U‐shape

orts the lowe

mandible

section

which

er teeth.

The c

round

that fi

joint

mand

craniu

each

mand

The co

‐ tria

from t

joins o

the m

The as

jaw w

condy

condyle

ded end of

its into the m

between

ible and

um. There is

side of

ible.

oronoid proc

angular pro

the mandibl

one of the c

andible.

scending ram

which joins t

yles.

‐ the

f bone

movable

the

the

one for

f the

cess

ojection

e which

chewing mus

mus ‐ th

he body of

4

scles to the c

he flatter, st

the mandib

Fig

cranium. The

raighter part

le to the co

gure 2: The Hum

ere is one fo

t on the side

oronoid proc

man Mandible

or each side of

es of the lowwer

cesses and tthe

TH

Th

HE MAXILLA

he maxilla, o

A (UPPER JA

or the upper j

AW)

jaw, is madee up of severr

sit

ch

Th

TH

Th

pa

bo

cu

ts in front of

heeks, the no

he maxilla is

the m

of the

HE TEMPER

he temperom

art of the cra

one surfaces

ushion.

F

f and just be

ose and the r

divided into

mouth. The h

e mouth. The

ROMANDIBU

mandibular j

anium called

s are separa

igure 3: The Hu

elow the cra

roof of the m

:

ard part is c

e softer part,

ULAR JOINT

joint (TMJ) i

d the tempor

ated by a ci

uman Maxilla

5

nium. It is a

al bones stu

ttached to

ck (or fused)) together, a

and forms

nd

tthe cranium tthe

mouth.

The

maxillary s

space tha

cheekbone

called the “h

the “soft pa

T (TMJ)

s the movab

ral bone. It is

ircular piece

the mouth.

of the face,

The

‐ a bit of bo

the maxilla

nose.

The

a curved pie

outwards fr

a part of th

The

the mouth,

ard palate”

alate”, is at th

ble joint bet

s a complica

e of softer c

e maxillary

sinus ‐

t sits just

and just abo

There is on

either side o

e anterior na

one which p

a at the low

e zygomatic

ece of bone

rom the max

e cheekbone

e palate

, separating

and it is tow

he back near

tween the m

ted joint and

cartilage wh

y antrum

‐ the air fill

t under t

or

led

the

ove the rooff of

e for each si

of the nose.

asal spine

pr

ide

otrudes froom

wer end of t

process

which exten

xilla and for

e.

‐ the roof

the nose a

wards the fro

the

‐

nds

ms

of

nd

ont

r the throat.

mandible and

d the two ha

ich acts like

d a

ard

e a

Th

an

ch

w

ro

sli

TH

A f

Th

he TMJ mov

nd forwards.

hewing, swa

hile some o

otation of th

iding movem

HE FORAMI

foramen is a

he foramina

Fig

Figu

ves up and

. It is in cons

llowing, talk

of these mov

e joint and s

ments.

INA

an opening o

are divided i

gure 4: The Hummovemen

re 5: The Huma

down, sidew

stant use du

king or laugh

vements inv

some others

or hole which

into the follo

man TMJ in actnts of the lower

an Foramina

6

ways

uring

hing,

volve

s are

h lets nerves

owing parts:

ion, causing r jaw

and blood v

Th

on the

Nerves a

travel to t

this.

Th

inferior d

the ascen

the inferio

vessels w

pass throu

Th

at the fron

Nerves ca

the blood

the palate

vessels pass tthrough bon

he mental fo

body of t

and blood

the lower lip

he mandibul

dental foram

ding ramus.

or dental ne

hich go to th

ugh this.

he incisive f

nt of the pala

alled incisiv

d which supp

e pass throug

foramen

the mandib

vessels whi

p pass throu

lar foramen

men ‐

A nerve call

erve and blo

he lower tee

foramen

e.

‐

ble.

ich

ugh

or

on

led

ood

eth

‐

ate.

ve nerves a

ply the fro

nd

n

gh this.

t f

THHE SALIVARRY GLANDS

Thhe salivary gglands produuce the cleaar liquid thaat is releasedd into the mmouth (salivva).

Thhere are threee pairs of mmajor salivarry glands andd many minoor glands. Saaliva lubricattes

thhe mouth annd start the breakdown of chewed ffood. It is mmade up of wwater, enzymme,

m

Th

ucin and pro

he salivary gl

The pa

otein.

land pairs ar

arotid

e the followiing:

gland,

saliva

called

the m

next t

is one

The s

‐ s

releas

front o

teeth.

The su

situate

releas

openi

This p

to eac

‐ salivary

the largest

, situated bbelow the ear. The

is released tthrough an oopening

the parotid

outh on the

o the upper

on each side

submandibu

situated und

ses saliva ju

d duct which

inside of the

molar teeth

e.

lar salivary

der the mand

ust

h enters

e cheek

h. There

y gland

dible. It

underneaath the

of the tongu

. There is one

ublingual sa

ed under t

se saliva f

ue, behind th

e on each sid

alivary gland

the tongue

from many

he front

de.

ds ‐

e. They

y small Figgure 6: The Human Salivary GGlands

ngs (ducts)

pair of saliva

ch other und

under the

ary glands s

er the tongu

tongue.

its next

ue.

7

THHE CERVICAAL VERTEBRRAE

Thhe cervical vvertebrae aree positionedd immediate

be readily d

ly posterior

istinguished

to the skull

from those

. They are tt

sm

an

Th

nu

th

G

Th

sa

th

st

ad

es

pr

th

th

Th

de

ai

Th

ex

ca

mallest amon

nd lumbar r

hrough each

umbered fro

he skull to the

ENERAL OV

he following

agittal sectio

he neck. Am

ructures

denoids, oro

sophagus, la

roximity bet

he tongue, t

he epiglottis

he epiglottis

etermines in

r or food flow

he pharynx i

xtends: the

avity) and the

Figure 7:

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VERVIEW OF

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OMY ELEME

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9

od and drink

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tuberosities

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10

THHE TOOTH

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ental pulp.

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e enamel

e entire nerve

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11

f the tooth f

ves that ente

tal pump is

F

filled with s

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commonly c

igure 11: The H

oft connecti

from a hole

called as the

Human Tooth

ive tissue. T

at the apex

“nerve” of t

his

of

the

TOOOTH DEVEELOPMENT

Infants

sm

te

th

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De

th

be

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sh

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maller than a

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eciduous Inc

he top and f

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eciduous Can

hape. There

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han the front

ave more tha

Figure 12: The DTeeth (milk

adults’ teeth

hrough. The

bout age 2 to

s teeth are:

isors: These

four at the

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are four alto

e a single roo

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t teeth and h

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The m

human

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Figure 13: The

12

en:

milk or decidu

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d, extracted

By the tim

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e coming th

gh after this

in late teens

uous teeth a

the ages of

and replace

me most pe

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.

re the first s

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e only teeth

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nt teeth and t

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there are 8 o

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ar surfaces f

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ition Sequence

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st teeth to

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come throu

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r at

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eeth have a

e age 16 to 2

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23 months a

ted

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ll because th

or chewing w

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remolars in a

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adults.

ween the agees of 1 to 2.55. Later on thhese teeth aare replaced by

Te

28

co

la

m

ar

th

Figure 14

eenagers and

8 Adult Tee

oming throu

rger than m

ore room fo

re 32 adult t

hrough if the

Figu

4: The Timeline

d Adults

eth: Adult

ugh at aroun

milk teeth. A

or the new

teeth altoge

jaw is not b

ure 16: The Per

e of the Primary

or permane

nd the age

As the jaw

adult teeth

ether but so

ig enough.

rmanent Dentit

13

y Dentition

ent teeth s

of 6. They

grows, ther

to erupt. Th

ometimes th

tion

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are

re is

here

e wisdom te

The Ad

Perman

the fro

them a

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are us

teeth t

disting

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root th

Perman

Figu

eeth have t

dult Teeth are

nent Incisor

ont teeth and

altogether (f

our at the b

ually the fir

to come thro

uished due

edge and the

hat they have

nent Canine

ure 15: The 28 A

rouble comi

ing

e:

rs. These a

d there are 8

four at the t

bottom). Th

rst permane

ough. They a

to their f

e one and on

e.

es: Also know

Adult Teeth

are

8 of

top

hey

ent

are

flat

nly

wn

e a more poas

al

s “eye teeth”

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”, these fron

root.

nt teeth hav ointed shapee. Being 4 in number, thhey

PrdeTh

Peroar

1s

m

2n

pe12

3r

wi– thprtodaca

remolars: Theciduous mohe deciduous

ermanent Mooot. They alsre first, secon

t Permanentolars and co

nd Permaneermanent m2 years.

d Permanentisdom teethif they comehere is not roperly and tooth in the famaged, or an become in

Figu

hese are theolars. The fous teeth do no

olars: These o have irregnd and third

t Molars: Theome through

ent Molarsolars come

t Molars: Co. They do noe through at enough spathey get impfront. The lathe gums anfected and q

ure 17: The Tim

e new adultur 1st premoot have prem

are the largeular or “bumpermanent

e four first page 6 to 8 y

s: The fouthrough at

ommonly knot erupt untiall, becauseace for thempacted often atter can somround the wquite painfu

14

meline of the Pe

t back teethlars erupt firmolars as bac

er back teethmpy” surfacemolars whic

permanent mears.

ur second around age

own as the il late teens sometimes m to erupt against the metimes be wisdom teetl.

ermanent Dent

h which reprst followed ck teeth, but

h and they ues with groovch come thro

molars are si

h

Figure 12agai

ition

place the firsby the four t just molars.

usually have ves called “fiough that ord

milar in size

2: A Wisdom Toinst its neighbo

st and seco2nd premola.

more than oissures”. Theder.

to the seco

ond ars.

one ere

ond

ooth erupting or tooth

Figthsuco

gure 20: A panoe primary teetccedaneous te

onsidered succe

oramic x‐ray ofh at these ageeeth because thedaneous teeth

f a 7 years old s. The develophey succeed thh.

Figure 19: D

15

child. One can ping permanentheir correspond

Deciduous and

notice the comt teeth up to tding primary te

Adult Teeth

mplex mix of thhe 2nd premoleeth. Permane

he permanent alar are also calnt molars are

and lled not

Figapincmoen

Figure

gure 22: Panorapical foramina,complete matuolars a radiogrnamel pearls.

Figure 23

e 21: Schematic

amic radiograp, especially inuration. Tooth raphic addition

3: Schematic de

c diagram of de

ph of a 9‐year‐on the maxilla, 12 is rotated an effect caused

epiction of dev

16

evelopment an

old female. All have not ye

about its axis. d by superimp

velopment and

nd eruption of t

of the permant assumed thNote in the bifosition of the

eruption of th

the primary de

nent incisors hae normal diamfurcation of throot trunks. T

e permanent d

ntition

ave erupted. Thmeter, indicate first permanThis is not due

dentition

heir ting ent e to

Figure 24: Pancomplete. Teechamber. Durithe mandible cThe neck and c

noramic radiogeth 35 and 45 ng the pubertacreated space condyle of the

graph of a 15‐have developal growth spurfor the buds omandible are n

‐year‐old femaped into taurort, dorsally andf the wisdom tnot yet fully de

ale. Root formdonts with a d cranially directeeth and theirveloped.

mation of the ecoronoapicallycted growth ofr root developm

erupted teeth y expanded puf the maxilla anment has begu

isulpndun.

Fac

Figure 25: Panoapical foramincompletely eru

oramic radiograna and the roupted but exhib

aph of a 20‐yeaoot canals exhbit a long axis t

ar‐old female. hibit normal dhat is oriented

Development diameter of ad slightly dorsal

of the dentitiodult age. The ly.

on is complete. third molars

Theare

17

Figgure 26: A commplete view of tthe Oral Anatomy

18

CHAPTER 2

PANORAMIC RADIOGRAPHY: A CLINICAL OVERVIEW

INTRODUCTION

Millions of dental panoramic radiographs are performed every year in a global basis.

Being a simple, quick and convenient technique as also as providing a respectful image

of the dentition and its related structures on a single film, with a relatively low dose in

comparison to other radiographic techniques, it is easy to understand why its popularity

has become so grown; and it is still growing.

A panoramic radiograph contains a substantial amount of diagnostic information. This

information, being sometimes difficult to be detected, finds itself upon the four basic

diagnostic regions in panoramic radiography:

1) The Dentoalveolar region

Figure 1: The Dentoalveolar region

19

2) The Maxillary region

Figure 2: The Maxillary region

3) The Mandibular region

Figure 3: The Mandibular region

20

4) The Temporomandibular joint region (abbreviated as TMJ), including the

retromaxillary and cervical regions.

Figure 4: The Temporomandibular Joint region (TMJ)

THE NORMAL PANORAMIC RADIOGRAPH

The normal panoramic radiograph contains a broad range of information that covers the

entire dentition and its surrounding structures, the facial bones and condyles and parts

of the maxillary sinus and nasal complexes.

Various interpretations of the normal panoramic radiograph exist in current literature,

so that the practitioner, the radiologist and the physician will be able to have an

appropriate comprehensive pattern of the technique and its imaging and diagnostic

potentials. However, it is crucial that each individual develops his/her own method of

interpretation according to:

a) the modality that is being used and its imaging programs and abilities, b) the clinical

cases that are taken place in general and c) the basic anatomic characteristics of the

population. The development of a consistent approach that ensures that all diagnostic

information in the panoramic radiograph is indeed read is absolutely essential.

Indicatively, four suggestions of interpreting the normal panoramic radiograph are

following:

21

A) Allan G. Farman (2007) remarks 50 distinct soft tissues, bony and dental landmarks

on a normal panoramic radiograph.

His approach on reading and evaluating the radiograph follows roughly the numerical

sequence of the figure below. It starts with the bony landmarks from the midline of the

upper jaw and nasal cavity, then back in the maxilla and zygomatic complex on each

side. The soft tissue shadows of the tongue and soft palate follow, and then the cervical

spine and its associated structures. Afterwards, the focus is on the contents of the

mandible starting from the midline and then progressing posterior on each side. Any

examination would be incomplete without a thorough evaluation of the soft tissues

anterior to the spine and inferior to the mandible. Lastly, there is the evaluation of the

area of chief complaint and the dental arches. While these regions draw the reader’s

attention automatically, the other features within the radiograph can be missed without

careful sequencing.

Figure 5: Interpreting a Normal Dental Panoramic Radiograph A

22

1. nasal septum 26. mandibular canal

2. anterior nasal spine 27. mental foramen

3. inferior turbinate 28. inferior border of mandible 4. middle turbinate 29. hyoid

5. superior turbinate 30. pharyngeal airspace 6. soft tissue shadow of the nose 31. epiglottis

7. airspace between soft tissue shadow of the upper border of tongue and hard palate

32. coronoid process of mandible

8. lateral wall of nasal passage 33. inferior orbital rim

9. maxillary sinus (antrum) 34. mastoid process

10. nasolacrimal canal orifice 35. middle cranial fossa 11. orbit 36. bite‐block for patient positioning

during panoramic radiography 12. infraorbital canal 37. chin holder (cephalostat) 13. zygomatic process of the maxilla 38. shadow of cervical spine 14. pterygomaxillary fissure 39. ethmoid sinus

15. maxillary tuberosity with developing third permanent molar tooth

40. angle of mandible

16. zygoma 41. crypt of developing mandibular third permanent molar tooth

17. zygomatico‐temporal structure 42. developing mandibular second premolar tooth

18. articular eminence of temporal bone

43. primary second molar tooth showing physiological root resorption

19. mandibular condyle 44. maxillary permanent central incisor tooth

20. external auditory meatus 45. maxillary permanent lateral incisor tooth

21. first cervical vertebra (atlas) 46. maxillary permanent canine tooth 22. second cervical vertebra (axis) 47. maxillary first premolar tooth 23. third cervical vertebra 48. maxillary permanent first molar

tooth 24. fourth cervical vertebra 49. ramus of mandible

25. mandibular foramen & lingual 50. pterygoid plates

23

B) Friedrich A. Pasler (2007) suggests the following reading of the panoramic

radiograph:

Figure 6: Interpreting a Normal Dental Panoramic Radiograph B

1. orbit 15. zygomatic arch, articular tubercle

2. intraoral canal 16. coronoid process

3. nasal cavity 17. condyle

4. nasal septum 18. external ear with external auditory meatus

5. inferior nasal concha 19. cervical vertebrae

6. incisive foramen, superiorly located anterior nasal spine, nasopalatine canal

20. temporal crest of the mandible

7. maxillary sinus 21. oblique line

8. palatal roof and floor of the nose 22. mandibular canal

9. soft palate 23. mental foramen

10. maxillary tuberosity 24. dorsum of the tongue

11. pterygoid processes (lateral and medial lamina) and the pyramidal process of the palatal bone

25. compact bone of the inferior border of the mandible

12. pterygopalatine fossa 26. hyoid bone

13. zygomatic bone 27. superimposition of the contralateral jaw 14. zygomaticotemporal suture

24

C) William S. Moore presents his landmarks of interest for the interpretation of the

normal panoramic radiography:

Figure 7: Interpreting a Normal Dental Panoramic Radiograph C

1. coronoid process 19. infraorbital canal

2. sigmoid notch 20. nasal septum

3. mandibular condyle 21. inferior turbinate

4. condylar neck 22. medial wall of maxillary sinus 5. mandibular ramus 23. inferior border of maxillary sinus 6. angle of mandible 24. posterolateral wall of max. sinus 7. inferior border of mandible 25. malar process

8. lingual 26. hyoid bone

9. mandibular canal 27. cervical vertebrae 1‐4

10. mastoid process 28. epiglottis

11. external auditory meatus 29. soft tissues of neck (look vertically for carotid artery calcifications here)

12. glenoid fossa 30. auricle

13. articular eminence 31. styloid process

14. zygomatic arch 32. oropharyngeal airspace 15. pterygoid plates 33. nasal air space

16. pterygomaxillary fissure 34. mental foramen

17. orbit 35. hard palate

18. inferior orbital rim

25

D) Having in mind the figure of a normal panoramic radiography, another suggestion for

its interpretation follows, by Eric Whaits (2006):

A. General Overview of the Entire Panoramic Film

1. Note the chronological and development age of the patient

2. Trace the outline of all normal anatomical shadows and compare their shape and

radiodensity

B. The Teeth

3. Note particularly: i) the number of teeth present, ii) stage development, iii) position,

iv) condition of the crowns (caries, restorations), v) condition of the roots (length,

fillings, resorption, crown/root ratio)

C. The Apical Tissues

4. Note particularly: i) the integrity of lamina dura, ii) any radiolucencies or opacities

associated with the apices

D. The Periodontal Tissues

5. Note particularly: i) the width of the periodontal ligament, ii) the lavel and quality of

crestal bone, iii) any vertical or horizontal bone loss, iv) any furcation involvements, v)

any calculus deposits

E. The Body and Ramus of the Mandible

6. Note: i) shape, ii) outline, iii) thickness of the lower border, iv) trabeculae pattern, v)

any radiolucent or radiopaque areas, vi) shape of the condylar heads

F. Other Structures

7. These include: i) the antra (note the outline of the floor, the anterior and posterior

walls and the radiodensity), ii) nasal cavity, iii) styloid processes.

26

As mentioned above, the “strategy” for the interpretation of a panoramic radiograph is

varies according to various and subjective factors. Ideally, one should create his/her own

permanent and unique method of reading a panoramic image, so that all included

diagnostic information can be detectable.

Apart from the methods of interpreting the whole normal panoramic radiograph, there

are also similar methods of interpretation specific regions, tissues or structures such as:

facial skeleton, maxillary sinus, retromaxillary space, external ear and TMJ region,

palatal bone, chin region and many others. The presentation of these methods does not

fit to the goals of this paper. However, the reference bibliography includes such

sections, for those interested in these subjects.

Errors in interpretation are commonly made in the maxillary and mandibular incisor

region. It is important to be aware of the normal appearances of the dental panoramic

image when assessing the mandibular bone density:

Lucency: Normal symmetrical lucency is common in the mandibular body inferior to the

premolar and molar apices and may be mistaken for a lytic lesion. The lucency is due to

the submandibular fossa on the lingual aspect of the mandible. The appearance is

exacerbated in middle‐aged and elderly women by reduced bone density. Artifactual

lucency over the mandibular angle is also produced by incorrect tongue positioning.

Figure 8: Coned panoramic tomograph demonstrating normalradiolucencies. The pseudolucency (air space) betw en thesoft palate and tongue (curved arrow), the normalmandibu ar lucency (straight arrows), the nasopharynx np)and oropharynx (op) are shown.

e

l (

27

Areas of increased density: The mandible may appear sclerotic in the midline owing to

superimposition of the density of cervical spine. However, intra‐oral densities may also

appear as an area of mandibular sclerosis.

Figure 9: There is an apparent area of sclerosis within the left lower mandible (arrows)

A very significant point concerning radiographic anatomy must be taken into

consideration. Representing the basis for radiographic interpretation, it follows its own

rules and demands understanding and knowledge of how x‐ray work, as well as the

normal anatomy of the irradiated spaces, depending on the radiographic technique

used. Analogous to this essential knowledge, the following basic rules must be obeyed

for every type of radiograph, including the panoramic technique:

- The tangential effect of x‐rays renders clearly visible in the irradiated space only

those hard tissues with either high density or significant thickness; thin lamella

which, at the moment of the exposure, are parallel or nearly parallel to the

central ray simulate hard tissue of significant thickness and therefore appear in

the radiograph as densely opaque. On the other hand, similar structures which,

at the moment of exposure, are perpendicular to the central ray or nearly so

may, even though they are relatively thick, appear transparent in the radiograph

because of the exposure data necessary to penetrate the tissue.

- The summation effect of x‐rays may lead to hard and soft tissue structures in the

field being exhibited more clearly, or they may disappear entirely depending

upon the selection of exposure data. For example, if soft tissues are projected

28

29

upon one section of the bone, it will appear more dense than adjacent areas

because the x‐ray beam is already ‘weakened’ when it hits the bone. On the

other hand, if an air‐containing space is projected onto a section of bone, the

situation is on in which the x‐ray beam is not weakened before it encounters the

bone, penetrates I readily and therefore eliminates the typical radiograph

features of bone. The first example is referred to as “addition effect”, and the

second example as “subtraction effect”. The situation in such cases has

absolutely nothing to do with radiographic signs of “sclerosis” or “resorption”.

Panoramic radiography is not an exception; it depicts in‐focus layers of various thickness

(but always thicker than 5mm), and thus may be classified as a type of zonography. In

the panoramic radiograph, the picture of the irradiated tissues is determined by the

tangential effect and the summation effect; however, in keeping with the principle of

tomography, all of the structures within the in‐focus layer are shown relatively distinctly

and somewhat enlarged, while all structures outside of the layer are depicted as blurred

and reduced in size or as blurred, broadened and enlarged superimpositions; such

appearance will depend upon whether the superimposed structures are between the in‐

focus layer and the film or between the in‐focus layer and the focal spot.

CHAPTER 3

PRINCIPLES OF FUNCTION

INTRODUCTION

The theory of dental panoramic tomography is complicated. Nevertheless, an

understanding is necessary of how the resultant radiographic image is produced and

which structures are in fact being imaged, so that a critical evaluation and for the

interpretation of this type of radiograph.

The difficulty in panoramic tomography arises from the need to produce a final shape of

focal trough which approximates to the shape of the dental arches.

An explanation of how this final horseshoe‐shaped focal trough is achieved is given

below. Before that, other types of tomography –which form the basis of panoramic

tomography‐ are described, showing how the result in different shapes of focal trough.

These include:

‐ Linear tomography using a wide or broad x ray beam

‐ Linear tomography using a narrow or slit x ray beam

‐ Rotational tomography using a slit x ray beam

30

Broad Beam Linear Tomography

The synchronized movement of the tubehead and film, in the vertical plane, results in a

straight linear focal trough. The broad x ray beam exposes the entire film throughout

the exposure.

Figure 1: Diagram showing the theory of broad beam linear tomography to produce a vertical coronalsection with the synchronized movement of the x ray tubehead and the film in the vertical plane. Usinga broad beam, there will be multiple centers of rotation (three are indicated), all of which will lie in theshaded zone. As all these centers of rotation will be in focus, this zone represents the focal plane orsection that will appear in focus on the resultant tomography. Note, the broad x ray beam exposes theentire film

Slit or Narrow Beam Linear Tomography

A similar straight linear tomograph can also be produced by modifying the equipment

and using a narrow or slit x ray beam. The equipment is designed so that the narrow

beam traverses the film during the tomographic movement. Only by the end of the

tomographic movement has the entire film been exposed. The following equipment

modifications are necessary:

‐ The x ray beam has to be collimated from a broad beam to a narrow beam.

‐ The film cassette has to be placed behind a protective metal shield. A narrow

opening in this shield is required to allow a small part of the film to be exposed

to the x ray beam at any one instant.

‐ A cassette carrier, incorporating the metal shield, has to be linked to the x ray

tubehead to ensure that they move in the opposite direction to one another

during the exposure. This produces the synchronized tomographic movement in

the vertical plane.

throughout the exposure.

31

‐ Within this carrier, the film cassette itself has to be moved in the same direction

as the tubehead. This ensures that a different part of the film is exposed to the x

ray beam throughout the exposure.

Figure 2: Diagram showing the theory of narrow beam linear tomography to produce a verticalcoronal section. The tomographic movement is produced by the synchronized movement of the xray tubehead and the cassette carrier, in the vertical plane. The film, placed behind the metalprotective front of the cassette carrier, also moves during the exposure, in the same direction asthe x ray tubehead. The narrow x ray beam traverses the patient and film, exposing a differentpart of the film throughout the cycle.

Narrow beam rotational tomography

In this type of tomography, narrow beam equipment is again used, but the synchronized

movement of the x ray tubehead and the cassette carrier are designed to rotate in the

horizontal plane, in a circular path around the head, with a single center of rotation. The

resultant focal trough is curved and forms the arc of a circle, as shown below. Some

important points to note are the following:

‐ The x ray tubehead orbits around the back of the head while the cassette carrier

with the film orbits around the front of the face.

‐ The x ray tubehead and the cassette carrier move in opposite directions to one

another.

‐ The film moves in the same direction as the x ray tubehead, behind the

protective metal shield of the cassette carrier.

‐ A different part of the film is exposed to the x ray beam at any one instant, as

the equipment orbits the head.

32

‐ The simple circular rotational movement with a single center of rotation

produces a curved circular focal trough.

‐ As in conventional tomography, shadows of structures not within the focal

trough will be out of focus and blurred owing to the tomographic movement.

Figure 3: Diagrams showing thetheory of narrow beam rotationaltomography. The tomographicmovement is provided by thecircular synchronized movement ofthe x ray tubehead in one directionand the cassette carrier in thehorizontal plane. The equipmenthas a single center of rotation. Thefilm also moves inside the cassettecarrier so that a different part of thefilm is exposed to the narrow beamduring the cycle, thus by the endthe entire film has been exposed.The focal plane or trough (shaded)is curved and forms the arc of acircle.

Dental Panoramic Tomography

The dental arch, though curved, is not the shape of an arc of a circle. To produce the

required elliptical, horseshoe‐shaped focal trough, panoramic tomographic equipment

employs the principle of narrow beam rotational tomography, but uses two or more

centers rotation.

There are several dental panoramic units available. They all work on the same principle

but differ in how the rotational movement is modified to mage the elliptical dental arch.

Four main methods have been used including:

33

‐ Two stationary centers of rotation, using two separate circular arcs

‐ Three stationary centers of rotation, using three separate circular arcs

‐ A continually moving center of rotation using multiple circular arcs combined to

form a final elliptical shape

‐ A combination of three stationary centers of rotation and a moving center of

rotation

Figure 4: The main methods that have been used to produce a focaltrough that approximates to the elliptical shape of the dental arch usingdifferent centers of rotation. A: 2 stationary, B: 3 stationary, C:continually moving, D: combination of 3 stationary and moving centers.

However, the focal troughs are produced, it should be remembered that they are 3‐

dimentional. The focal trough is thus sometimes described as a focal corridor. All

structures within the corridor, including the mandibular and maxillary teeth, will be in

focus on the final radiograph. The vertical height of the corridor is determined by the

shape and height of the x ray beam and the size as shown below.

34

As in other forms of narrow beam tomography, a different part of the focal trough is

imaged throughout the exposure. The final radiograph is thus built up of sections, each

created separately, as the equipment orbits around the patient’s head.

Figure 5: The figure shows how the height of the three‐dimensional focal corridor is determined. Theheight (x) of the x ray beam is collimated to just cover the height (f) of the film. The separation of thefocal trough and the film (d) coupled with the 8⁰ upward angulation of the x ray beam results in thefinal image being slightly magnified.

FOCAL TROUGH (Image Layer)

The focal trough or the image layer of a panoramic radiograph is a 3‐dimensional curved

zone. Objects inside this zone are reasonably well defined. The anatomical structures

which lie inside the image layer are depicted with the minimum of unsharpness and

distortion. Going outside this layer, unsharpness is growing. Objects outside the focal

trough are blurred, magnified or reduced in size and sometimes they are distorted to

the extent of not being visible or recognizable. As it can be easily concluded, the focal

trough and all its diagnostic information is all in all the very essence of a panoramic

radiograph.

35

The exact shape of the focal trough (horseshoe curve) varies with the brand of the

equipment used. The factors that affect its size are variables that influence image

definition:

‐ Arc path

‐ Velocity of the film and the x ray tube head

‐ Alignment of the x ray beam

‐ Collimator width

The location of the focal trough can change with extensive machine use. In this way, recalibration may be necessary if consistently suboptimal images are produced.

Figure 6 The Focal Trough. The closer to the center of the trough (dark zone) an anatomic structure is positioned. The more clearly it is imaged on the resulting radiograph.

36

Figure 7: Gradual formation of a panoramic tomograph over an 18‐second cycle, strating how a different part of the patient is imaged at different stages in the cyclillu e.

37

FORMATION OF THE IMAGE LAYER

As the x ray tube and the cassette holder are mounted at opposite ends of a gantry,

during the exposure the x ray beam and the cassette rotate around the patient. The x

ray beam is collimated both at the tube head and immediately in front of the film screen

cassette. The effect of the collimation is to create a beam that is vertically long although

horizontally narrow. Control of the rotational movement and film velocity is achieved by

computer software and mechanical gearing.

The projection technique employed in rotational panoramic radiography is unique, as

there are two foci of projection working simultaneously.

In the vertical plane the situation is analogous to conventional radiography where the x

ray tube focus acts as the focus of projection. Consequently, the magnification in the

vertical plane (MV) is as follows:

where FFD is the focus to film distance and FOD is the focus to object distance.

In the horizontal plane, the effect of the narrow collimated beam combined with its

motion creates the appearance that the point of divergence for the x rays is the rotation

centre of the beam. Therefore, this point acts as an effective focus for the x rays in the

horizontal plane and the distance between this point and the object is termed the

effective projection radius (R). The magnification in the horizontal plane (MH) is

therefore:

As the effective rotation centre is nearer the object than the conventional focus, the

effective projection distance is always smaller than the conventional focus to object

distance. Consequently, the magnification in the horizontal plane is greater than the

magnification in the vertical plane, leading to geometric distortion.

38

Figure 8: Creation of an effective focus of projection

The rotational movement of the x ray beam also means that every ray in the beam will

project the image of a discrete object point onto the film plane at a different position.

The image of a discrete object point would therefore be portrayed as a horizontal line at

the film plane if the film remained stationary during the exposure producing motion

unsharpness. However, by moving the film in the same direction as the beam and

selecting an appropriate velocity of movement, the film can be made to match the

projected path of an object plane within object. Object points within this plane are

therefore depicted with minimum motion unsharpness at the film plane.

The velocity of the film relative to the beam also affects the horizontal magnification of

points within the object. It has been shown that an object will be sharply depicted at the

film plane where the following equation is standing:

where VB is the velocity of the beam, VF is the velocity of the film, FFD is the focus to

film distance and R is the effective projection radius.

The horizontal magnification therefore depends not only on the geometric properties of

projection but also on the relative velocity of the film to the beam and consequently the

horizontal magnification is a non‐linear function with object depth.

39

The position of the focal trough within the object is not constant but depends on the

relative velocity of the film to the beam. As the FFD is generally constant, increased

acceleration of the film velocity relative to the beam shifts the position of the focal

trough away from the rotation centre and towards the film cassette, with a

corresponding increase in the effective projection radius. Decreasing the film velocity

relative to the beam moves the position of the focal trough towards the rotation centre

and away from the film cassette, thereby reducing the effective projection radius.

As the width of the focal trough is proportional to the effective projection radius, it is

possible to alter the size and position of the focal layer by adjusting the relative velocity

of the film to the beam and thereby create a focal layer that corresponds to the

idealized shape of the jaws.

In many modern systems the projection of the jaw is achieved by using an effective

rotation centre that is continuously moving throughout the exposure. In these units, the

x ray beam is always directed perpendicularly to the path of the effective rotation centre

throughout the exposure. Consequently, the effective projection radius varies

continuously throughout the exposure, being wider in the lateral aspects of the jaw than

in the anterior regions. As a result, the focal layer is narrower in the anterior region of

Figure 9: Diagram of beam projection in modern dental panoramic x ray units.

40

the jaw where the effective projection is smaller. Furthermore, as the size of the

effective projection radius also influences the horizontal magnification, the horizontal

magnification of object points outside the focal trough is more marked in the anterior

regions of the jaw compared to the lateral regions.

The path of the beam also determines the angle at which the central ray of the beam

traverses the object. Ideally, to aid interpretation and measurement, the central ray of

the beam should be projected perpendicularly to the object throughout the exposure.

However, the projection angle between the central ray and the object varies throughout

the exposure, only approaching perpendicularity in the anterior regions of the jaw.

Distortion effects are therefore produced by the oblique projection angle between the

beam and some regions of the jaw. As in conventional radiography, this effect leads to

compression of objects in the resulting image. It should be noted however, that this

effect is independent of both geometric distortion and motion unsharpness and

therefore distortion effects due to oblique projection occur even at the focal trough

position.

GEOMETRIC DISTORTION

For object points located outside the focal layer, the greatest source of distortion is the

geometric distortion caused by the discrepancy between the horizontal and vertical

magnification factors. The degree of distortion can be assessed using a relationship

termed the Distortion Index:

At the focal trough, where an object’s vertical and horizontal magnification are equal,

the DI is one and geometric distortion is minimized. A distortion index greater than one,

indicates that the horizontal magnification of the image is greater than the vertical

magnification. This effect occurs if the velocity of the film is greater than the velocity of

the beam. This occurs if the object is displaced away from the focal trough position

towards the centre of rotation (i.e. towards the beam).

41

Conversely, a distortion index less than one indicates that the vertical magnification is

larger than the horizontal one in the image and it occurs if the velocity of the beam is

greater than the velocity of the film. This occurs when the object is displaced away from

the focal trough position towards the film.

Figure 10: Magnification and x ray tube focal spot size.

Displaced towards the rotation centre

of the beam

Placed at the focal trough

Displaced towards the film

Table 1: Distortion effects. Relationship between type of distortion and displacement from the focal trough.

42

Screen Film and Intensifying Screens

A beam of x ray photons that passes through the dental arches is reduced in intensity

(attenuated) by absorption and/or scattering effects of photons out of the primary

beam. The pattern of the photons that exists the subject, the remnant beam, conveys

information about the structure and the composition of the absorber. This is why the

remnant beam has to be “written” on an image receptor, in order to be diagnostically

useful.

Dental panoramic x ray units use a combination of screen film and intensifying screens.

The advantages of this combination are the increased sensitivity and better contrast.

The screens have much higher x ray absorption efficiency (510 times) than a

photographic film and will also produce a great number of light photons per x ray

photon absorbed, thus yielding a more efficient film exposure. The x ray exposure can

often be reduced by factor of 10‐50, depending on the screen characteristics.

The sensitivity can vary depending on the screen thickness. The thicker the screen, the

higher the absorption efficiency. However, a thicker screen will also result in an

impairment o spatial resolution. The light produced in the screen will have a longer

distance before it hits the film and it will therefore be more diffused than for a thinner

screen. More sensitive screens can also be produced using larger phosphor crystals in

the screen material. This will lower the spatial resolution and will also increase the noise

level.

Due to the higher atomic number of the screen material compared to the silver halide

grains, the film‐screen combination is always relatively more sensitive to higher energy x

rays than film alone. This extends the use of film‐screen combinations to techniques

which use higher energy beams, compared to film alone.

Thus, apart from the panoramic technique, screen‐film combinations have been one of

the most important components in all modern radiology.

The Screen Film

Screen film is different than dental intraoral films in that it is designed to be particularly

sensitive to visible light rather than to x radiation because this film is placed between

two intensifying screens when an exposure is made.

The intensifying screens absorb x rays and emit visible light, which exposes the screen

film. Silver halide crystals are inherently sensitive to ultraviolet (UV) and blue light (300

to 500 nm) and thus are sensitive to screens that emit UV and blue light. When film is

43

used with screens that emit green light, the silver halide crystals are coated with

sensitizing dyes to increase absorption. Because the properties of intensifying screens

vary, the dentist should use the appropriate screen‐film combination recommended by

the screen and film manufacturer so that the emission characteristics of the screen

match the absorption characteristics of the film. In panoramic radiography fast films

that require less radiation exposure are mainly used, as fine image detail is not available

because of the movement of the x ray tube head during the exposure period.

The design of screen films changes constantly to optimize imaging characteristics. As an

example, Kodak has introduced T‐Mat films, which have tabular‐shaped (flat) grains of

silver halide. The tabular (T) grains are oriented with their relatively large, flat surfaces

facing the radiation source, providing a larger cross‐section (target) and resulting in

increased speed without loss of sharpness. In addition, green‐sensitizing dyes are added

to the surface of the tabular grains, increasing their light‐gathering capability and

reducing the crossover of light from the phosphor layer on one side of the intensifying

screen to the film emulsion on the other. Kodak’s Ektavision system also coats the film

base with an absorbing dye to prevent crossover of light from one screen to the other

emulsion. These properties increase both the speed of the film and the sharpness of the

image. Sterling uses tabular grains in its Cronex I OT film, and Imation coats its XDA+ and

XLA+ film base with an anti‐crossover agent as well.

Figure 11: T grains of silver halide in an emulsion of T‐Mat film (A) are larger andflatter that he smaller, thicker crystals in an emulsion of conventional film (B).Note that he flat surfaces of the T grains are oriented parallel with the filmsurface, facing the radiation source. (Courtesy Eastman Kodak, Rochester, N.Y)

44

INTENSIFYING SCREENS

Wilhelm Conrad Roentgen, along with the x rays, discovered the intensifying screens. He

was experimenting with high energy cathode ray tube and had enclosed the tube in

black cardboard. When passing a high voltage discharge through the tube, he noticed a

faint light from a piece of paper left on a work bench. The paper was covered with a thin

layer of barium platinocyanide. This first “intensifying screen” sent out fluorescent light

of inorganic salts (phosphors) which emit

fluorescent light when excited by x ray radiation. The sheets are used to intensify the

At

is

into eV

at y

is 850. Approximately, half of these will escape from the screen to

expose the emulsion. About 100 light photons may be sufficient to form one latent

: calcium

tungstate screen (CaWO4) and rare earth screens (La2O2S:Tb, Gd2O2S:Tb, Y2O2S:Tb),

38.9 lower

caused by the x rays.

An intensifying screen is a sheet of crystals

effect of x rays during exposure of x ray film.

The intensifying screen or a pair of screens is nearly always used with x ray film in

radiography. Film may be used as the only radiation detector but having a relatively low

atomic number (that of silver halide), film is relatively radiolucent. direct exposure of

film, only about 5% of the x ray photons will be absorbed by the film and react with the

emulsion. For comparison, a high speed calcium tungstate screen will absorb

approximately 40% of the x ray photons. Furthermore, each absorbed x ray photon will

be converted into many light photons. The efficacy of the screen in converting x rays

into light photons is called the intrinsic conversion efficiency. The efficiency of calcium

tungstate about 5%. A 50 keV x ray photon when absorbed by calcium tungstate (by

photoelectric absorption), will be converted about 17,000 light photons of 3

energy 100% efficiency. Since the efficiency is onl 5%, the actual number of light

photons emitted

image centre.

There are two major types of phosphors and therefore intensifying screens

where terbium (Tb) is often used as an impurity or activating substance.

During the 70’s, the principal material in intensifying screens was calcium tungstate

(CaWO4). Nowadays, the principle materials are based on gadolinium and lanthanum

substances. Calcium tungstate suffers from the drawback that the K‐edge for W in the

absorption curve is situated at 69.5 keV. This means that the CaWO4 screen is quite

insensitive to the part of the x ray spectrum with photons of energies between 50 and

69 keV when compared to gadolinium or lanthanum screens, which have their Kedges

lower at 50.2 and keV respectively, due to their atomic number. Since this

part of the x ray spectrum often contains a significant fraction of the x rays that exit

45

from the patient, the sensitivity is increased using these newer materials. This is

furthermore amplified by the fact that the new materials have a higher light conversion

efficiency, which means that more light photons are generated per x ray photon

absorbed. Compared to CaWO4, the newer screens produce about 3.5 to 4 times more

reen part of the spectrum but smaller

ones also in the blue, blue‐green and yellow regions. The term “green screen” may be

sed. It is absolutely necessary to use green sensitive film with these screens to make

sure that useful transmitted radiation is not lost.

light.

Figure 12: X ray absorption spectra for calcium tungstate (W) and gadolinium (Gd) based intensifying screens.

The spectral output of the phosphor must be matched to the response of the film.

Calcium tungstate screens emit blue light of continuous spectrum with a peak

wavelength at about 430 nm. The term “blue screen” refers both to the screen itself and

to the blue sensitive film used together with the Ca WO screen. Rare earth screens emit

light in narrow lines with strong peak(s) in the g

u

46

Figure 13: Spectrum of light emitted from calcium tungstate (CaWO) and rare earth screen (GdOS), respectively, in comparison with the light sensitivity of blue sensitive

and green sensitive film.

There are many factors affecting the speed of a screen. The phosphor type determines:

‐ The x ray radiation absorption efficiency

‐ The radiation to light conversion efficiency

‐ The thickness of the phosphor

The fraction of x rays absorbed by a pair of calcium tungstate screens is about 20‐40%

depending on the speed (determined mainly by screen thickness), while rare earth

screens absorb about 60%. The radiation to light conversion efficiency of calcium

tungstate is about 1/3 or 1/4 of that of the film‐screen cassette. The relative speed of

film‐screen combinations is normalized to 100 which corresponds the basic calcium

tungstate screen with the basic film. Speed values vary from 20 and 50 (slow screens)

through 100, 200, 400 and 800 to 1,600.

An essential basic feature of the two screen types is related to the position of the K edge

on the energy axis. Tungsten (W) being a heavy element has its K edge at 69.5 keV, while

that for rare earth elements is in the vicinity of 50 keV. Most x ray spectra used in

conventional radiography have their mean energy between 40‐50 keV, signifying that

also for this reason rare earth screens are more effective than CaWO4 in absorbing x ray

quanta.

47

Compared to film only, the contrast of the same film together with screens is always

higher. The reason for this is not precisely known.

DIGITAL PANORAMIC RADIOGRAPHY

An image is said to be a digital one when it is composed of separate (distinct) elements.

Each element is called a “picture element” or a pixel. If an image is displayed on the

computer monitor and the pixel is smaller than the smallest detail the viewer’s eye can

see, it is hard to determine that the image is indeed a digital one. If this is not the case,

that is the individual pixels can be spotted, the eye views the image as a mosaic of

pixels.

Each pixel can only take on a limited number of gray shades. The number of possible

gray shades depends on the number of bits (binary digits) that are used to store a pixel.

A 1‐bit pixel can only take two values (0 or 1 – that is black or white). An 8‐bit pixel can

take any one of 256 (28) values. A 16‐bit pixel can take more than sixty five thousand

grayscale values (216). The total number of bits that are used to store an image is the

number of pixel times the number of bits per pixel.

Most systems of digital panoramic radiographs use on the final depiction mostly 8 bits

(thus, 256 different grey levels). Newer systems deposit the image as data of 10, 12 or

16 bits (thus 1024, 4096 or 65536 different grey levels). However, these systems lay the

final image out using 8‐bit data and 256 different grey levels. It is generally accepted

that the human eye can only distinguish about 20 magnitudes of light intensity, and is

probably unable to discern all 256 gray levels that a standard computer monitor can

display. Thus, a human eye cannot distinguish totally a little more than 100 different

grey levels. Indeed, in cases where these levels of grey find themselves on the same

radiograph, then the number of the distinguished levels is limited between 30 and 40.

For example, for the panoramic system Dimax I (Planmeca Oy, Helsinki, Finland) the

functional and true size of the pixel that presents the final image is 132 μm. This pixel

size delivers a maximum theoretical resolution, which is the Nyquist frequency, of 3.78

cycles per mm.

There are three methods available to produce digital panoramic images. First, it is

possible to digitize conventional analog film radiographs through secondary capture

using transparency scanners or specialized digital cameras. Film scanners and digitals

cameras, though, can be used to produce digital images only from an analog film

radiograph.

48

In general, secondary capture is best achieved with a good quality scanner having a

radiography adaptor (i.e. scanning light in the lid to pass light through the radiograph. A

sharp black and white photograph setting is preferred. Excellent scanners for this

purpose for a sufficient high quality system have a cost varying from 600$ to 1,500$.

Scanners are preferred to digital cameras as they practically eliminate optical distortion

and the reflection from the surface of the radiograph that would otherwise reduce

image quality. Film scanners do not change the need to continue making radiographs

with x ray film. They introduce additional time‐consuming activity to scan images but

that is the price for continuing the use of analog film radiographs while digitally storing

images.

No matter the quality of the film scanner, scanned images can only be as good as the

priginal film radiographs. The advantage is that the user can scan and archive the

existing film files over time and determine if digital panoramic imaging is needed

without spending a lot of money in purchasing sophisticated equipment. While Schultz

et al. (2002) found the sensitivity for detection of low contrast simulated bone lesions

was greater with film than after digitization, the absolute differences were small.

Figure 14: Nikon CoolPix scanner withtransparency adaptor in lid sufficient forextraoral radiograph duplication.

Figure 15: Panoramic radiograph placed fordigitization in an alternative flat bedscanner, the Epson FinePix Z2 withtransparency adaptor.

The result of this method is apparently substandard in comparison to the following two

methods. However, these two technologies have the same principles of function with

those that are applied in endodentulous radiographies.

49

Solid‐state systems using the technology of Charged‐Coupled Device (CCD) or

complementary metal oxide semiconductor (CMOS) comparable to the computer chip

found in a digital photographic camera

McDavid et al. (1995) presented and evaluated the first experimental system for

panoramic radiography with the use of CCD technology. This original system was a

modification of the panoramic machine OP10 (Instrumentarium Imaging, Finland). The

rotation time around the patient’s head remained stable and the same with the

equivalent conventional system, but the combination of film and rare earth screens had

been replaced by a narrow linear sensor CCD. The height of this sensor was

approximately 15 cm and its width a few millimeters.

During the last years, different systems of digital panoramic imaging using CCD

technology have been introduced into the market. The procedure of the production of

the image remains the same. Solid‐state digital x ray detectors are based on a silicon

chip that permits the acquisition of an image. Such a chip consists of a myriad of pixels

and each pixel captures a small quantity of energy (usually light from a scintillator) and

converts this radiant energy into electricity. For panoramic radiology, this generally

involves a charged coupled device (CCD) or complementary metal oxide semiconductor

(CMOS) of sufficient dimensions to cover the secondary slit of the panoramic machine

(i.e. tall and narrow). The solid‐state chip (CCD or CMOS) converts radiant light photons

into electrons when a scintillator is used. The ability of detectors to capture radiant

energy is no longer limited to visible photon as cadmium telluride can produce electrons

directly on impact of x ray photons. Most systems, however, still use a scintillator layer,

similar to the scintillators that are used as intensifying screens in analog film panoramic

radiography. An example of one of the earliest commercialized digital panoramic

systems was that of the Trophy Digipan adaptor for the Instrumentarium OP 100.

Figure 16: The Trophy Digipan adaptor used with Instrumentarium OP 100 panoramic system in place of the film cassette. A variety of “add‐on” systems from several different vendor sources are now available for most panoramic systems.

50

Figure 17: Schematic representation of a solid‐state detector. Unlike analog x ray film radiography, the receptor is stationary and the image for each segment is read out in

appropriate sequence.

Solid state systems are available both to retrofit an existing panoramic system and as

integrated units dedicated to a specific panoramic x ray generator. A potential concern

with retrofitting a unit is that if something does go wrong, the owner may be in the

position of working together with the manufacturer of the panoramic system, the

manufacturer of the retrofit system and the installer.

As with analog film, the panoramic image is pieced together during the scan. Unlike

analog film radiography, the receptor is stationary and the image for each segment is

read out in appropriate sequence. As it was mentioned above, in conventional

panoramic imaging, the position of the image layer is determined by the velocity of the

film in relation to the x ray beam. In digital panoramic radiography using CCD

technology, it is not the film that is moving in order to form the image properly but the

charges themselves as they are read‐out. Thus, the velocity by which the pixels give their

data for the final imaging is exactly the same with the velocity of the movement, in the

scintillator’s plane, of the projections of the anatomical structures and elements inside

the focal trough. In this way, the image is formed partially and almost simultaneously

with the patient’s radiation, thus in real time.

51

A direct practical consequence of this fact is that the user can control at any time of the

radiation the quality of the final imaging. If the user sees that the patient is not properly

positioned during the radiation, he/she is able to interrupt the procedure and re‐

position the patient, so that a more correct imaging will be achieved.

Researchers report that the width of the x ray beam which scans every moment the

patient to form the image, is much more narrow in digital panoramic imaging using CCD

technology, in relation to conventional panoramic radiography. This happens due to the

high sensitivity of the CCD and to the attempt of bounding the x ray beam, using special

collimators, exactly at the width of the slit linear sensor. This offers an important

advantage, which is a significant reduce of the radiation dose of the patient. Farman et

al. (2000), as well as Dula et al. (2008), confirmed this experimentally.

Additionally, MacDavid and Dove (1995) report two direct practical consequences. The

zone in which the depiction’s sharpness is maximum is larger, thus the positioning of the

patient is not as much important as in conventional procedures and in this way some

small positioning errors may not be of such significant importance. However, many

times the over‐projection of other anatomical regions cannot be avoided, resulting in

the black‐out of elements of diagnostic interest. For example, the spine can break the

depiction of the front regions, or the depiction of the lateral regions of the mandible

being blocked by the respective regions of the other side.

Moreover, as the CCD sensor is much more sensitive to the combination of film and rare

earth screens, a reduction of the mA of the machine (less quantity of radiation) may be

achieved with the same kV, as in conventional methods, or even higher. In this way, a

reduction in the patient’s dose is possible. Higher photon energy is less harmful for the

patient. The contrast of the final image will be lower in this case, with higher voltage.

This happens due to the different absorption of the radiation, depending on the beam

energy when the beam enters through matter (an object). However, this is something

that can be overcome, as there is the possibility of editing the image, adjusting the

contrast.

The percentage of dose reduction in digital panoramic radiography using CCD

technology is not always the same. It is a fact that a reduction of the radiation dose

similar to intraoral radiography is not possible, due to the fact that in conventional

panoramic radiography the dose is already very low, as a consequence of the film‐rare

earth screen combination. The dose reduction percentage that is reported in the global

bibliography varies from 20% to up to 40% related to conventional panoramic

52

radiography. In this case, the final image will have an intense noise. However, using the

editing techniques that digital imaging systems offer even such an image may be

corrected and used for diagnostic purposes.

Units which use the technology of Storage Phosphor Plates (SPP)

In the middle of the 80’s, Kashima et al. (1985) presented the first digital panoramic

radiograph using a Storage Phosphor Plate (SPP). This technique has been improved

over the years, until it reached a widespread level of acceptance all over the world.

Today, a variety of companies use this technology.

In this technique a special plate, with the same size (30x15 cm) as in conventional

panoramic radiography, is used. Such plates contain a phosphor layer that deposits the

energy of the photon with which it interacted. Hence, the name “storage phosphor” is

used. After its irradiation, the plate is placed in a special scanner or digitizer where it is

scanned by radiation of specific wavelength. When a portion of the plate is illuminated,

it emits light that is photomultiplied and collected by a digital imaging chip. The image

appears through sophisticated electronic processes (photomultiplier, analog to digital

converters) in a monitor of a computer.

Photostimulable phosphor systems dedicated to dentistry are available from a number

of manufacturers. Each system is comprised of the phosphor plates and a laser scanner

that interfaces with a computer. The plates can be quite expensive, costing from 500

euro up to 2,000 euro each. While extraoral plates are not as sensitive to scratching as

are the intraoral ones, care must still be taken not to scratch or contaminate them. The

plates are very sensitive to ambient light which can erase much of the latent image.

Furthermore, they need extensive exposure to light in order to completely erase the

image before reuse. On the other hand, storage phosphor systems are versatile in that

they can be used with a wide range of different x ray systems.

It is of particular importance that this technique can be applied upon every conventional

panoramic system. The only modification needed, is the placement in the holder of the

panoramic machine, of the Storage Phosphor Plate, instead of the combination of film‐

rare earth screen. The only extra equipment needed, to gain the final image, is the

specialized scanner or digitizer. Many manufactures offer themselves the scanner along

with the conventional panoramic machine.

53

A basic characteristic of the plates used in this technique, is that they do not have

picture elements (pixels). The latter are formed during the procedure of the laser

scanning of the plate and their exact size depends on the degree of focalization of the

laser radiation. For example, the DenOptix system (Gendex) uses a pixel size of 170 μm,

when the resolution in the scanner is determined to be 150 dots per inch (150 dpi). This

pixel gives out a maximum theoretical resolution, the Nyquist frequency, equal to 2.95

cycles / mm.

The phosphor plates have a very high dynamic range of irradiation. Thus, with the use of

this technique the quantity of the radiation targeting the patient (mA) may be reduced,

without any loss of the diagnostic quality of the final image. The dose reduction

percentage, related to conventional techniques, is approximately at 20%. The time

period of the radiation cannot be reduced, as it is always stable for a specific unit

depending on the whole rotation movement that it makes.

Figure18: Imaging using storage phosphor plate.

54

Figure19: Loading a photostimulable phosphor plate into a soft cassette.

Interoperability

It is not unusual to review film radiographs that are decades old –especially when

demonstrating “classical” radiographic features of disease entities at a continuing

education forum. Archived film images that are decades old are usually still of high

quality and can be viewed by anyone who happens to have a view box to transmit light

through the radiographs.

One might question whether the digitized or digital versions will be as readily accessible

as the analog film versions decades into the future. The likelihood of being able to

retrieve digital images is dependent upon both hardware and software/file format

considerations.

Regarding hardware issues, one simply needs to back up all files on new media as they

become accepted. If one intends to use digital images they periodic storage hardware

upgrades must be performed. Regarding the matter of software/file format

interoperability, the digital x ray industry and practice management system vendors are

presently working together to facilitate digital image interoperability using specifications

from the DICOM (Digital Image Communication) standards that were developed initially

for medical radiology. This specification includes image format rules and associated

information for transmission of radiographs used in dentistry including intraoral surveys

and panoramic images.

55

However, no guidelines or specifications will guarantee interoperability. Interoperability

needs to be demonstrated practically. Such practical demonstrations were initiated at

the ADA Annual Congress in New Orleans in 2002, where ten companies demonstrated

that interoperability of their image files could be archived satisfactory. Similar practical

demonstrations have been made with DICOM validation at all ADA Annual Sessions,

through at least until the time of publication of this book. Each time there are more

vendors involved.

Interoperability within the DICOM Standard is important so that the dentist can

integrate data from different digital sources and read diagnostic images referred from

outside sources where different systems may have been used. Otherwise there could be

inconvenience both for the patient and for the practitioner.

Radiation Dosage

Unlike intraoral radiology, the switch to digital panoramic imaging does not generally

result in a substantial dose reduction to the patient. In fact it is sometimes necessary to

actually increase dosage to optimize image quality when using digital systems.

With intraoral x ray film radiography, the emulsion is directly sensitive to x rays, so

adding a scintillating screen can improve the efficiency with which x rays are detected.

However, for extraoral radiography, an intensifying screen is generally employed –and

this is not so very different from the scintillating layer used with solid‐state detectors.

Gijbels et al. found no difference in exposure settings or organ doses between analog x

ray film and digital panoramic radiography using Photostimulable phosphor plates.

COMPARISON BETWEEN FILM AND DIGITAL PANORAMIC IMAGING

Digital panoramic radiography includes the following essential properties:

‐ Images of diagnostic quality

‐ Radiation dose similar or reduced compared to film radiography

‐ Lossless archiving (storage of the full original radiographic image)

‐ Interoperability of image format so that the patient’s information can be

conveniently shared when professionally necessary

Below there is a summary of the advantages and disadvantages of the two categories.

56

ADVANTAGES DISADVANTAGES

FILM TECHNIQUE

• Low initial cost, especially for manual processing

• Often already in place • l No changes or additiona

training required • Known entity – proven

output • f Relatively low cost ooperation

• Excellent diagnostic clarity possible if exposed and processed optimally

• Widely accepted

• Cost of consumables such as film and processing solutions

• ent Cost of processing equipmand darkroom space

• Time consumption in film processing and processor maintenance

• Processed film images are rarely optimal

• Used processing chemicals are toxic to the environment

• d Film radiograph storage anretrieval can be problematic

• Duplicates made from film radiographs are invariably inferior to the original images

DIGITAL X RAY

IMAGING

e is Time saving as therno chemical processing

More consistent in quality for the same reason

Digital images ease communication with patients

Digital images are readily stored and retrieved

Digital radiology opens the way to electronic interchange

Consultation can be expedited

Digital images allow perfect “clone” duplication and backup

Post‐processing can help optimize the diagnostic yield

Digital radiology eliminates environmental silver contamination from spent fixer

Added initial cost for equipment if film imaging is already used

Need for additional computers, monitors, networking, backup storage

Detectors (both solid‐state and phosphor systems) can add an important cost of the panoramic system

Changes in operations, systems and procedures require an investment in time and involve a learning curve

Not all digital image formats are identical at this moment, so interoperability can be problematic both in the same office and when making outside referrals

Eventually hardware obsolescence

Table 2: Advantages and disadvantages of conventional and digital panoramic imaging (Farman, 2007).

57

Equipment

There are several different dental panoramic tomographic units. Although they vary in

design, all of them consist of three main components:

‐ An x ray tubehead and its power supply, producing a narrow fan‐shaped x ray

beam, angled upwards at approximately 8⁰ to the horizontal

‐ A cassette and cassette carriage assembly

‐ Patient positioning apparatus including light beam markers

Figure 20: A modern panoramic x ray unit.

The equipment should have a range of tube potential settings, preferably from 60 to 90

kV. The beam height at the receiving slit of cassette holder should not be greater than

the film in use (normally 125 mm or 150 mm). The width of the beam should not be

greater than 5mm. Equipment should be provided with adequate patient‐positioning

aids incorporating light beam markers. New equipment should provide facilities for field

limitation techniques.

58

Almost all modern panoramic machines have a continuous‐mode of operation and

produce a so called continuous image showing an uninterrupted image. X ray production

is continuous throughout an uninterrupted tomographic cycle, during which the centers

of rotation are adjusted automatically. However, one machine was developed which

produced a so called split‐mode image because the radiographic image is split by a

broad, vertical, white, unexposed zone, with duplication of the midline. The split mode

equipment is now only of historical interest.

There are a number of different panoramic machines available in the market. The

machines operate on the same image formation principles and only differ in the added

features. Panoramic machines employ a single‐phase x ray robe that requires an average

cool down period of 5 minutes between exposures for maximum tube life. Machines

have an upright construction with an adjustable vertical tube height range typically of 3

feet (0.91 m) to 6 feet and 4 inches (1.92 m) from the floor. The entire machine may be

freestanding with a heavily weighted base or wall mounted. The cassette holder and x

ray tube are attached to a carrier that mechanically rotates them at a preset path and

speed around the patient’s head during each exposure. These variables stay consistent

from patient to patient unless the technologist changes the location or width of the

focal trough which is adjustable to accommodate different facial profiles.

Two types of cassettes are made for panoramic machines: hard and floppy. The type of

cassette to be used is determined by the manufacturer. The standard film sizes available

for panoramic imaging are 6’’x 12’’ and 5’’x 12’’. Sizes are also determined by the

machine manufacturer. Cassettes incorporate rare earth screens and use 400 speed

film. Specific film types may be chosen to optimize bony or soft tissue detail.

Most modern panoramic machines allow the patient to stand up for the exposure. A

chair or wheelchair can be accommodated. All panoramic machines have some type of

guides to help position and hold the patient within the focal zone. This commonly

includes a platform for the chin to rest on and a bite stick with grooves for the upper

and lower central incisors, placing the oral cavity within the focal plane. For edentulous

patients there may be a separate, specialized positioning device that is used in place of

the bite stick. Many machines use laser light guides at the infraorbitalmetal (IOM) line

and along the midsagital plane to help the technologist adjust the patient into position,

as well as guide bars that can be secured alongside the head to help the patient

maintain the correct position throughout the exposure.

Almost every panoramic machine produces standard panoramic films as well as

specialized projections of the (TMJ) such as transmaxillary projections and either single

images or multiple “cuts”. Even the least sophisticated machines typically offer multiple

59

views of the TMJ area including lateral images with the mouth open and closed,

producing all 4 images on one film. A wide array of programs specifically designed to

evaluate the TMJ are available with more advanced machines. Additional programs

allow for multilayered exposures of the area in the frontal, transmaxillary and lateral

projections to evaluate fractures, arthritic changes and abnormalities in the size, shape

and position of the condylar head. Programs can also assess the articular processes.

More sophisticated panoramic machines offer a variety of programs that produce

tomographic images of predefined areas of almost any area of the head. Using a series

of computer controlled programs that use various tube head and film motions, including

multidirectional, these machines can perform coronal, sagittal and cross‐sectional

images through a predetermined area. These programs can be helpful in the assessment

and treatment of sinusitis, neoplasm, fractures, foreign bodies, air‐fluid level detection

in the sinuses, mucosal changes of the sinuses and soft tissue calcifications. Many

panoramic machines can be fitted with a film holder that supports an 8’’ x 10’’ film used

for static skull views using the panoramic x ray tube head.

Figure 21: The Instrumentarium OP 200D (PaloDEx, Tuusula, Finland)

60

Patient Positioning

The exact positioning techniques vary from one machine to another. However, there are

some general requirements that are common to all machines and these can be

summarized as follows:

Patients should be asked to remove any earrings, jewellery, hair pins, spectacles,

dentures or orthodontic appliances.

The procedure and equipment movements should be explained, to reassure

patients.

A protective lead apron should not be used as it can interfere with the final

image.

Patients should be placed accurately within the machines using the various

head‐positioning devices and light‐beam marker positioning guides. (In some

units the patients face away from the equipment and towards the operator and

in others the patient faces the other way round.)

Patients should be instructed to place their tongue into the roof of the mouth so

that it is in contact with the hard palate and not to move during the exposure

cycle (approximately from 9 to 18 seconds).

Appropriate exposure setting should be selected, typically in the range of 70‐100

kV and 4‐12 mA.

The positioning of the patient’s head within this type of equipment is critical –it must be

positioned accurately so that the teeth lie within the focal trough. The effects of placing

the head too far forward, too far back or asymmetrically on relation to the focal trough

are quite easy to take place. The parts of the jaws outside the focal trough will be out of

focus. The fan‐shaped x ray beam causes patient malposition to be represented mainly

as distortion in the horizontal plane, i.e. teeth appear too wide or too narrow rather

than foreshortened or elongated. These and other positioning errors are shown later.

However accurately the patient’s head is positioned, the inclination of the incisor teeth,

or the underlying skeletal base pattern, may make it impossible to position both the

mandibular and maxillary teeth ideally within the focal corridor.

61

Field Limitation Techniques

In panoramic radiography, there is the ability to program the equipment to only radiate

certain parts of the jaws when specific information is required, rather than the entire

dentition. This results in a significant radiation dose reduction. A variety of these so‐

called field limitation techniques are possible.

Figure 22: Diagrams showing the position of the mandible in relation to the focal troughwhen the patient is not positioned correctly. A) The patient is too close to the film and infront of the focal trough. B) The patient is too far away from the film and behind the focaltrough. C) and D) The patient is placed asymmetrically within the machine.

62

Figure 23: Diagrams showing the vertical walls of the focal trough in the incisorregion and the relative positions of the teeth with different underlying dental orskeletal abnormalities. A) Class I, B) Gross class II division 1 malocclusion with largeoverjet. C) Angle’s class II skeletal base. D) Angle’s class III skeletal base. The shadedareas outside the focal trough will be blurred and out of focus.

The two figures below represent the relative movements of the x ray tubehead, cassette carrier and film during an exposure cycle of a continuous‐mode panoramic unit.

Figure 24: Initially the left side of the jaw is imaged (position 1). As the x ray tubehead movesbehind the patient’s head to image the anterior teeth, the cassette carrier moves in front of thepatient’s face and the centre of rotation moves forward along the dark arc (arrowed) towardsthe midline.

63

Figure 25: The x ray tubehead and cassette carrier continue to move around the patient’shead to image the opposite side and the centre of rotation moves backwards along the darkarc (arrowed) away from the midline. Throughout the cycle, the film is also continuouslymoving as illustrated, so that a different part of the film is being exposed at any one moment.

64

CHAPTER 4

RADIATION EFFECTS, DOSES AND PROTECTION CONCERNING QUALITY CONTROLLING ON

PANORAMIC RADIOGRAPHY

INTRODUCTION

X rays have taken their name due to their unknown nature, at the time of their discovery

(1895) by Roentgen. Being one of the different types of ionizing radiation and being able

to penetrate the human tissues, they are a form of high energy electromagnetic

radiation and part of the electromagnetic spectrum, which also includes lower energy

radio waves, as well as television and visible light.

Radiation Wavelength Photon Energy Radio, television and radar waves

3x104 m to 100 m 4.1x10‐11 to 1.2x10‐2 eV

Infra‐red 100 m to 700 m 1.2x10‐2 eV to 1.8 eV Visible light 700 nm to 400 nm 1.8 eV to 3.1 eV Ultra violet 400 nm to 10 nm 3.1 eV to 124 eV X and gamma rays 10 nm to 0.01 pm 124 eV to 124 MeV Table 1: The electromagnetic spectrum ranging from the low energy (long wavelength) radiowaves to the

high energy (short wavelength) x and gamma rays (White, 2000).

X rays consist of wave packets of energy, called photons. A photon is equivalent to one

quantum of energy. The x ray beam, as used in diagnostic radiology, is made up of

millions of individual photons. Although the production and interactions of x rays with

matter is an essential knowledge, in this project such a presentation is out of its interest

as such background information is presupposed.

65

SOURCES OF RADIATION

Everyone is exposed to some form of ionizing radiation from the environment. The

sources of radiation may be either natural or artificial. These include:

Natural Radiation Artificial Radiation Cosmic radiation from the earth’s atmosphere

Fallout from nuclear explosions

Gamma radiation from the rocks and soin the earth’s crust

il Radioactive waste discharged from nuclear establishments

Radiation from ingested radioisotopes, e.g. 40K, in certain foods

Medical and dental diagnostic radiation

Radon and its decay products, 222Rn is a gaseous decay product of uranium that is present naturally in granite. As a gas, radon diffuses readily from rocks through soil and can be trapped in poorly ventilated houses and then breathed into the lungs.

Radiation from occupational exposure

Table 2: Natural and artificial sources of radiation (Whaites, 1996).

Figure 1: The distribution of natural and artificial radiation. Natural radiation contributes more exposure than artificial radiation. Note that medical x ray diagnosis is the largest component of artificial radiation.

66

In the UK, an individual’s average dose from background radiation is approximately 2

mSv per year, while in the US it is estimated approximately at 3.6 mSv. Having these

numbers in mind, one can refer more safely to the numbers of doses of the medical

diagnostic radiographies.

As indicated above, medical x ray diagnosis produces the largest exposure of all artificial

sources of radiation (11%). This should not surprise anyone, as the millions of x ray

examinations that are made every year worldwide contribute to the total radiation

doses which add up through arithmetic progression. As such techniques are widespread

all over the world, it is crucial to find out whether some proportion of this exposure

could and should be avoided. The relatively very low doses that are produced from a

single x ray examination of any kind should not loosen neither the criteria by which an x

ray examination is decided nor the standards of the proper functioning of the x ray units

and their proper usage.

Classification of the biological effects

Three main categories classify the biological damaging effects of ionizing radiation:

Somatic Deterministic Effects

Somatic Stochastic Effects

Genetic Stochastic Effects

Somatic Deterministic Effects

These are the damaging effects to the body of the person that will definitely result from

a specific high dose of radiation. Examples include skin reddening and cataract

formation. The severity of the effect is proportional to the dose received and in most

cases a threshold dose exists below which there will be no effect.

Somatic Stochastic Effects

Stochastic effects are those that may develop. Their development is random and

depends on the laws of chance or probability. Examples of somatic stochastic effects

include leukemia and certain tumors.

These damaging effects may be induced when the body is exposed to ant dose of

radiation. Experimentally it has not been possible to establish a safe dose (a dose below

which stochastic effects do not develop). It is therefore assumed that there is no

67

threshold dose and that every exposure to ionizing radiation carries with it the

possibility of inducing a stochastic effect.

The lower the radiation dose, the lower the probability of cell damage. However, the

severity of the damage is not related to the size of the inducing dose. This is the

underlying philosophy behind present radiation projection recommendations.

Somatic effects are further subdivided into:

‐ Acute or immediate effects, appearing shortly after exposure, e.g. as a result of

large whole body doses

‐ Chronic or long‐term effects, becoming evident after a long period of time, the so

called latent period (20 years or more), e.g. leukemia.

DOSE WHOLE BODY EFFECT 0.25 Sv Nill

0.25 – 1.0 Sv Slight blood changes, e.g. decrease in white blood cell count 1 – 2 Sv Vomiting in 3 hours, fatigue, loss of appetite, blood changes.

Recovery in a few weeks 2 – 6 Sv Vomiting in 2 hours, severe blood changes, loss of hair within 2

weeks. Recovery in 1 month to year for 70% 6 – 10 Sv Vomiting in 1 hour, intestinal damage, and severe blood

changes. Death in 2 weeks for 80‐100% > 10 Sv Brain damage, coma, death. Table 3: Summary of the main acute effects following large whole body doses of radiation

Genetic Stochastic Effects

Mutations result from any sudden change to a gene or a chromosome. They can be caused by external factors, such as radiation or may occur spontaneously.

Radiation to the reproductive organs may damage the DNA of the sperm or egg cells. This may result in a congenital abnormality in the offspring of the person irradiated. However, there is no certainty in this, so all genetic effects are determined as stochastic.

A cause‐and‐effect relationship is difficult, if not impossible, to prove. Although ionizing radiation has the potential to cause genetic damage, there are no human data that show convincing evidence of a direct link with radiation. Risk estimates have been based mainly on experiments with mice. It is estimates that a dose to the gonads of 0.5 – 1.0 Sv would double the spontaneous mutation rate. Once again it is assumed that there is no threshold dose.

68

Harmful Effects Important in Dental Radiology

In dentistry, the sizes of the doses used routinely are relatively small and well below the

threshold doses required to produce the somatic deterministic effects. However, the

somatic and genetic deterministic effects can develop with any dose of ionizing

radiation. Dental radiology does not usually involve irradiating the reproductive organs,

thus in dentistry somatic stochastic effects are the damaging effects of most concern.

The precise mechanism of how x rays can cause damaging effects is not yet fully known

but two main mechanisms are thought to be responsible:

• Direct damage to specific targets within the cell

• Indirect damage to the cell as a result of the ionization of water or other

molecules within the cell

A photon strikes upon a molecule of water:

1. H2O H2O+ + e‐

2. The positive ion immediately breaks up: H2O H+ + OH

3. The electron (e‐) attaches to a neutral water molecule: H2O + e

‐ H2O‐

4. The resulting negatively charged molecule dissociates: H2O

‐ H + OH‐ 5. The electrically neutral H and OH are unstable and highly reactive

and called free radicals. They can combine with other free radicals, e.g: H + H H2 (hydrogen gas) OH + OH H2O2 (hydrogen peroxide)

The hydrogen peroxide can then damage the cell by breaking down large molecules like proteins or DNA.

Table 4: A diagrammatic summary of the sequence of events following ionization of water molecules

leading to indirect damage to the cell (Whaites, 1996)

Estimating the Dose and Risk of Panoramic Radiography

Quantifying the risk of somatic stochastic effects, such as radiation‐induced cancer, is

complex and controversial. Data from groups exposed to high doses of radiation (i.e.

radiotherapy, or survivors of nuclear accidents like Hiroshima or Chernobyl) are analyzes

and the results are used to provide an estimate of the risk from low doses of radiation

encountered in diagnostic radiology.

69

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Gibbs (1980) estimated the risk to be between 2 and 7x10‐6 and Bengtsson (1978)

4.2x10‐6. Since much of this work was undertaken, several international organizations

have suggested that the risk may be greater than previously estimated. Over the same

period of time the design of panoramic machines has changed and rare earth

screen/film combinations have become more widely used, resulting in a reduction in

computed the average effective dose for a panoramic examination to be 6.7μSv; this

figure is associated with an estimated risk of fatal malignancy of 0.21x10‐6.

Despite these encouraging findings, it should be emphasized that the lower levels of risk

are associated with new equipment. Horner and Hirschmann (1990) described the

various methods of limiting patient dose in panoramic radiography. The facility for field

size reduction is associated with a reduction in absorbed dose of 85% and effective

efficients and assuming the use of rare earth screen/film combinations, White (199

of 50%, when the TMJs are excluded from the field. However, it is likely that the higher

levels of dose and risk reported by previous researchers will remain valid as long as older

equipment remains in clinical use. For example, certain types of equipment using a

circular scanning motion incorporating three centers of rotation produce doses between

3 and 16 times higher than those with an elliptical system, due to the proximity of

rotational centers to the mandible and parotid glands. A study carried out in France

showed this type of equipment to be the most widely used. Furthermore, a survey of

panoramic equipment in the UK found that a higher dose than appropriate was being

delivered during use of 70% of this equipment.

Although abdominal lead protection is clearly inappropriate in panoramic radiography,

some researchers have recommended the use of a lead thyroid collar in younger

patients because of the relatively high anatomical position of the gland. However,

because the primary beam does not strike the patie

examination, a thyroid shield must logically be placed on the back of the neck. This runs

the risk of attenuating useful parts of the primary beam and obscuring areas of the

mandible on the radiograph.

71

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72

MMain Methods of Monittoring and Measuring Radiation DDose

Thhere are 3 main devices ffor monitorinng and meassuring radiation dose:

Film BBadges

Thermmoluminesceent Dosimeteers (TLDs)

‐ BBadge

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73

Advantages

‐ Provides a permanent record of dose received

‐ May be checked and reassessed at a later date

‐ Can measure the type and energy of radiation encountered

‐ Simple, robust and relatively inexpensive

Disadvantages

‐ No immediate indication of exposure – all information is retrospective

‐ Processing is required which may lead to errors

‐ The badges are prone to filter loss

TLDs

They are used for personal monitoring of the whole body and/or the

extremities, as well as measuring the skin dose from particular investigations

They contain materials such as lithium fluoride (LiF) which absorb radiation and

then release the energy in the form of light when heated

The intensity of the emitted light is proportional to the radiation energy

absorbed originally

Personal monitors consist of a yellow or orange plastic holder, worn like the film

badge for 1‐3 months

Advantages

‐ The lithium fluoride is re‐usable

‐ Read‐out measurements are easily automated and rapidly produced

‐ Suitable for a wide variety of dose measurements

Disadvantages

‐ Read‐out is destructive, giving no permanent record, results cannot be checked

or reassessed.

‐ Only limited information provided on the type and energy of the radiation

‐ Dose gradients are not detectable

‐ Relatively expensive

74

Ionization Chambers

They are used for personal monitoring (thimble chamber) and by physicists

(free‐air chamber) to measure radiation exposure

Radiation produces ionization of the air molecules inside the closed chamber,

which results in a measurable discharge and hence a direct read‐out

They are available in many different sizes and forms

Advantages

‐ The most accurate method of measuring radiation dose

‐ Direct read‐out gives immediate information

Disadvantages

‐ They give no permanent record of exposure

‐ No indication of the type or energy of the radiation

‐ Personal ionization monitors are not very sensitive to low‐energy radiation

‐ They are fragile and easily damaged

Measurements using phantoms

Phantom measurements in dental radiography are usually performed on

anthropomorphic phantoms in order to derive organ doses and thereby determine the

effective dose and/or the energy imparted to the patient.

Measurements in anthropomorphic phantoms are performed using TLDs positioned in

drilled holes in the phantom. General principles for the use of TLDs should be followed.

Patient Dosimetry

For patient dose measurements in panoramic projections, the measured quantity is the

air kerma‐length product, PKL. The PKL is the integral of the free in air profile of the air

kerma across the front side of the slit of the secondary collimator. Methods using a CT

chamber or a stack of TLDs for the measurement of PKL will be described. The air kerma‐

area product, PKA, is obtained as PKA=PKLH, where H is the height of the x‐ray beam at the

secondary collimator.

75

List of Equipment

The equipment used for panoramic projection comprises:

‐ Calibrated cylindrical ionization chamber and electrometer

‐ Chamber support

‐ Thermometer and barometer

‐ TLDs and a jig for mounting the dosimeters in front of the secondary collimator

may be used as an alternative to the pencil ionization chamber. Dosimeter

thickness and their diameter should be about 1 mm or less and 3 mm,

respectively. Dosimeters should have had their individual sensitivity correction

factors established or dosimeters within a selected sensitivity range should be

chosen

‐ Film and a ruler (for screen‐film systems)

Methods

The air kerma‐length product is measured using either a calibrated cylindrical ionization

chamber or an array of TLDs. The air kerma‐length product is immediately obtained

using an ionization chamber whereas use of TLDs requires several procedures before the

result is registered. When neither a cylindrical ionization chamber not TLD is available,

direct film could be used as described by Napier. The latter method requires calibration

of the film in terms of air kerma and careful handling of film development (IAEA, 1996).

Measurement of the air kerma‐length product using a cylindrical ionization chamber and

electrometer

1. Position the cylindrical ionization chamber in front of the secondary collimator (slit),

at the centre of the slit and perpendicular to its length direction

2. Make sure that the space between the chamber and the headrest is sufficient when

the secondary collimator is rotated.

76

M

1.

tim

sig

ca

2.

3.

pe

tu

ra

F

Measurement

Select a set

mes the slit w

gnal obtaine

an be identifi

Pack the ch

Position the

erpendicular

ube, includin

ay beam.

Figure 5: Experkerma‐area

t of the air ke

t of TLDs wit

width. Keep

ed without ir

ied in calibra

ips in a tube

e tube with t

r to the leng

g insertions

rimental arrang product for a d

c

erma‐length

h the sum of

another thre

rradiation. La

ations and m

of PMMA.

the TLDs in f

gth of the sli

for intraora

gement for meadental panoramhamber

77

product usin

f the thickne

ee dosimete

abel each ind

measurement

ront of the s

t and at its

al film for me

asurements of mic unit using a

3.

th

se

tu

cy

do

an

4.

st

th

5.

an

. Expose

hree times u

ettings of

ube load

ng an array o

ess sufficient

rs for measu

dividual dos

ts.

secondary co

center. A jig

easurement

the air a CT

a

ycle d

the chamb

using standa

tube voltag

an exposd u

an

osimeter rea

record t

adings, M1,

ber

ard

ge,

ure

the

MM2

nd M . 3

. Repeat ste

tandard

ep 3 for othher

seettings used in

he clinic.

. Record thee temperatuure

nd pressure.

of TLDs

t to cover a l

urement of th

length of thr

he backgrou

ree

nd

imeter so thhat its readinngs

ollimator wit

g may be us

h the tube a

ed to hold t

xis

the

hht, H, of thee x‐of the heig

4.

Re

Expose TLD

ecord the set

s using stand

ttings.

dard settingss of tube volltage, tube looading and eexposure cyccle.

5. Arrange forr the dosimeeters to be reead. Record the readings, M1, M2, ……, Mn, from tthe

exxposed dosimmeters and the readings,

6.

M

1.

th

0.

2.

sc

Repeat mea

Measurement

Position the

he ionization

5.

Develop the

canner.

Figure 6slit of receivinover ththe soldthe outpointinWilliam

asurements f

t of the heigh

e film in fro

chamber wa

e film and m

6: Schematic oa panoramic xng slit is facilite slit. Beam leder markers. Tter markers by g upwards, as s

ms and Montgo

for other sta

M01, M02 an

ndard setti

d M03, for thhe unexposedd dosimeterss.

nngs used in thhe clinic.

of the jig used tx‐ray unit usinated by the trngth is

to measure theng TLDs. Positiangular windo

e dose profile tioning of the ows in the jig,

across the recejig in front owhich are cen

eivingof thentered

measurred from the ddeveloped filmss using the imaage ofThe inner markkers are separaated by a distance of 120 mmm and150 mm. The jig is mountedd with the diagonal solder maarkers

(afteshown, to indicmery)

cate the orienttation of the deeveloped films r

ht of the x‐raay beam at thhe secondaryy collimator sslit

nt of the collimator slit,, at about thhe same locaation as wheere

as located annd expose thhe film to an optical denssity of less thhan

easure the hheight of the on the film uusing a rulerx‐ray beam or

78

HVL measurement

1. Set up the x‐ray equipment for the chosen examination. Suppress the tube movement

2. Select the tube voltage that would be used for a routine clinical examination.

as to avoid the effect of scattered radiation.

ifficult for the panoramic equipment unless

the width

e a detector with a smaller volume and try

to cover the maximum area of the detector.

5. Select a tube loading so that the dosimeter readings with and without the attenuator

values M1, M2 and M3.

s without any attenuator. The thickness of attenuators is selected so

that their value encloses the expected HVL of the beam.

8. Expose the detector again without any attenuator (steps 5 and 6) and record the

easured value.

Calculations

red signal for various

attenuator thicknesses. The HVL value measured during a quality assurance program can

, of the dosimeter readings.

if possible.

3. Centre the dosimeter in the x‐ray beam. The detector should be mounted free in air in

such a way

4. Collimate the beam to achieve conditions for narrow beam geometry. The beam

should just cover the detector. This may be d

of the beam can be increased. In this case, us

are within the rated range of the instrument.

6. Expose the detector three times and record measured

7. Repeat step 6 for a set of three Al attenuators and the same tube loading as that used

for measurement

m

Measurements of the air kerma‐length product using a cylindrical ionization chamber

and electrometer

1. Calculate the HVL of the beam by interpolating in measu

be also used.

2. Calculate the mean value,

79

3. Calculate the air kemra‐length product, PKL, from the mean dosimeter reading, ,

using the following equation:

ion quality Q used during measurement. It is

the dosimeter can be neglected and that no

correction has been applied for this effect.

The correction factor, kTP, given by:

273.2273.2

,

kTP is the correction factor for temperature and pressure, , is the calibration

coefficient for the radiation quality Q0 obtained at the temperature T0 and pressure P0

and kQ is the correction factor for the radiat

assumed that the leakage signal of

is

Measurement of the air kerma‐length product using an array of TLDs

1. Calculate the mean value of the background reading, , from background dosimeter

n), calculate the background corrected dosimeter reading,

Mi, from the exposed dosimeter, , and the mean background dosimeter reading, ,

using the following equation:

r the individual sensitivity of the i‐th dosimeter. This

factor is a constant for dosimeters grouped so that the sensitivity of dosimeters in the

3. For i‐th dosimeter (i = 1, …, n), calculate the air kerma, K , from the background

between irradiation of the dosimeter and its readout. The

Q ends on HVL of the beam that should be established using the

diagnostic dosimeter:

readings, M01, M02 and M03 ( 3⁄ ).

2. For i‐th dosimeter (i = 1, …,

,

where factor fs,i is used to correct fo

group lies within a selected range.

i

corrected dosimeter reading, , using the TLD calibration coefficient, , , for the

reference radiation quality, Q0, the correction factor, kQ, for the radiation quality used

and the correction factor, kf, that corrects for the effect of fading of the

thermoluminescence signal

correction factor, k , dep

,

80

4. Calculate the air kerma‐length product, PKL, using the following equation, in which Δd

is the thickness of a single TLD:

equation. In this

equation, PK is the air kerma‐length product obtained through the above equation and

H is the height of the x‐ray beam at the secondary collimator slit:

e relative standard

have to be included in the overall

is about 10.5%.

he user should establish the actual measurement uncertainty using the principles

described in the relative bibliography.

Establishment of the air kerma‐area product

Calculate the air kerma‐area product using through the following

L

Estimation of uncertainties

The uncertainty in the measurement of the air kerma can be estimated with a cylindrical

ionization chamber during panoramic projections. The value of relative expanded

uncertainty for measurements of the air kerma‐length product is again 6‐13%,

depending on the measurement scenario selected. Assuming that the maximum

difference of a measured slit height from the actual height is 2%, th

uncertainty for this effect is 1.2%. The expanded uncertainty for the measurement of

the air kerma‐area product using a cylindrical chamber is 6.4‐13.2%.

The uncertainty in measurements made with TLDs is discussed above. The relative

expanded uncertainty (k=2) of 10% was adopted. Additional contributions from

positioning of the dosimeters and measured slit height

uncertainty. The value of the relative expanded uncertainty (k=2) in measurements of

the air kerma‐area product using TLDs

T

81

Example

A panoramic dental unit is typically operated at 70 kV and 15 mA for a period of 15 s.

The air kerma‐length product was measured at a secondary collimator using a calibrated

dosimete s

mGy∙cm/reading and 0.98, respectively. The correction factor, kTP, for temperature and

pressure was 1.002. The measured air kerma‐length product is:

llimator slit was measured as 12.5 cm.

The air kerma‐area product is thus calculated as:

ncertainty (k=2) in the measurement is 6.4%.The air kerma‐area product is

written as:

114 7 ·

CT chamber. The reading of the r wa 0.923.

The calibration coefficients, , and kQ, for the dosimeter were 10.02

0.923 10.02 · 0.98 1.002 9.082 ·

The height of the x‐ray beam at the secondary co

9.082 · 12.5 113.53 ·

For scenario 3 (reference type detector and all corrections applied), the relative

expanded u

82

Worksheets

Determination of the air kerma‐length product and the air kerma‐area product for

e:___________________________________________________

No.:__________

_____ mm X ray beam height (H): _________ mm

_____ /N: ________ e of calib: _______

ressure P0 (kPa): __________ Temperature T0 (oC): _______

4. Dosimeter reading and calculation of air kerma‐length product and air kerma‐area

Mean dosimeter rea

o .

panoramic projection using a cylindrical diagnostic dosimeter

User:_________________________________ Date:____________________

Hospital or clinic nam

1. X ray equipment

X ray unit and model: __________________________________ Room

Slit width: ___

2. Dosimeter

Dosimeter model: _____ _____________ S __ Dat

Calibration coefficient ( , )*: ______ · / · /

Reference conditions: HVL (mm Al): _______________ Field size: _______________

P

3. Exposure conditions

Starting tube voltage (kV): _______ Tube current: ________ mA Time: ______s

Ambient conditions: Pressure P (kPa): ______ Temperature T (oC): ____ kTP = _______

product**

Dosimeter reading (M1, M2, M3): _______________ ding : ______

Pressure P (kPa): ___ Temperature T ( C): ____ .

= _______***

kQ = ______________

Calculated value of air kerma‐length product , ·

Calculated value of air kerma‐area product /10 __________ ·

_______________

_________

HVL (from 5 below) = ___________ mm Al

e overall calibration coefficient is calculated as a product of the two separate calibration coefficients.

an example for one setting. The measurements should be repeated for all settings used in clinical practice

*** For dosimeters with a semiconductor detector, kTP = 1

* This is the calibration coefficient for the whole dosimeter, including the detector and the measurement assembly. For systems with separate calibration coefficients for the detector and the measurement assembly, th

** This is

83

5. Determination of HVL

Dosimeter readings should be obtained for filter thicknesses that bracket the HVL. The ing

Filter ness (mm Al)

Dosimeter ading (M) (mGy)

verage dosimeter reading, , at zero thickness

____________ )

Interpolated HVL: _____ mm Al

first and last read s, M01 and M02 are made at zero filter thickness.

thick re A

0.00

0.00

84

Determination of the air kerma‐area product using an array of TLDs

User: ______________________________ Date: __________________

Hospital or clinic name: ____________________________________________________

__ Room No.:_________

h: ________ mm Slit height (H): _________ mm

TL

Al kQ for measurement set‐up: ________

): __________ cm

s (M1, M2, M3): _____________ _

n un

1. X ray equipment

X ray unit and model: _________________________________

Slit widt

2. TLDs

Identification markings on D sachet (if any): __________________________________

Calibration coefficient ( , ) for TLDs: ___________________________ mGy / reading

Reference beam quality (HVL): ______ mm

Dosimeter thickness (Δd

3. Exposure conditions

Tube voltage (kV): _____________

4. Dosimeter readings and calculation of the air kerma‐area product

Background reading ____________ ____________

Mea backgro d ⁄ _ Fa e __

No. Dosimetereading

Corrected a ing

Individual nsitivity

Air erma

No. Dosimetereading

Corrected ading

Individual nsitivity

Air erma

3 _____ ding corr ction (kf) = _

r re d se k r re se k

, Air Kerma, ,

ir kerma‐length product, ∑ ______________A ·

Air kerma‐area product, /10 ___________ ·

85

Doose Area Prroduct

Th

pa

sid

in

in

th

th

ca

an

he dose area

atient absorb

de of the pat

from of the

dependent o

he further aw

he device inc

alculated by

nd the patien

a product –

bs. It is usua

tient where

e x ray tube a

of the distan

way from th

creases, and

DAP, the siz

nt.

DAP is a m

ally measure

the radiation

and passing

nce between

e x ray tube

d the dose

ze of the me

measurement

ed behind th

n enters the

a beam thro

n the x ray tu

e this measu

itself decrea

easuring dev

t of the amo

he multi‐leaf

body, by att

ough it. The d

ube and the

urement is ta

ases. The do

vice and the

ount of radi

collimator,

taching a me

dose area pr

measuring d

aken, the mo

ose to the p

distance to

iation that t

that is, on t

easuring dev

roduct (DAP)

device becau

ore the size

patient can

the x ray tu

the

the

ice

) is

use

of

be

ube

=

Th

DA

ch

x

he

do

ad

pe

m

in

DAP

here are seve

AP meter ca

haracteristic

ray tube and

ead. This cha

ose measur

dvantage of

erf

eter

or

is rel

med in

a

terfere with

Figure 7: measurindecreasessize of the

P

eral DAP me

an eliminate

of panoram

d detect all

aracteristic m

rements in

this method

real time pa

atively trans

the x ray ex

X ray tube is ng device incres with greater e measuring de

ters availabl

problems a

ic units, sinc

radiation in

makes DAP

panoramic

d is that DAP

atient exami

sparent and

amination.

as great as doeases with gredistance to thevice enables it

86

le globally. T

rising from t

e it be moun

cident on th

meter very e

c radiology

P measureme

inations, sinc

d therefore

ose area for 10eater distance he tube. Thus, t to detect all o

The use of a

this special

nted on the

he patient’s

effective in

y. Another

ents can be

ce the DAP

does not

(Gy* m2) cc

00cm or 200cmto the x ray DAP is the samof the radiation

Figu

m, because thetube. But theme at each pon.

ure 8: Real time

e size of thee dose itselfosition if the

e DAP measureement.

Diagnostic Reference Levels (DRLs) deriving from DAP measurements

are defined as dose levels in groups of standard sized patients or standard

hantoms, for typical examinations and for broadly defined typed of equipment. These

levels should not be exceeded for standard procedures when good and normal practice

levels for panoramic

radiography. In Greece, for this technique, the report of such levels has already started

alo

the adoption of the 75 percentile as an

appropriate DRL value.

DRLs

p

is applied with regard to diagnostic and technical performance.

In this way, DRLs can play an important role in clinical practice to guarantee the

performance of diagnostic equipment and as a support to improve techniques and

procedures. Many countries have reported diagnostic reference

to take place by several publications.

The European Commission Radiation Protection Report No 109 (2004), ng with the

majority of the studies published, considers the frequency curve of a number of

examinations and their doses, and proposes th

Below, there are some indicative values from the European Commission.

COUNTRY/DATE OF RESULTS OF SURVEY PROPOSED/SET DRLs

PUBLICATION Occipital ESD: Occipital ESD:

‐ 0.7 mGy ‐ Mean 0.53 mGy ‐ Range 0.25‐0.87

Gy

Spain mGy

‐ Third Quartile 0.66 m

2001

F inland2000

DAP: ‐ Mean 94 mGy

cm2 ‐ Range 34‐254

mGy cm2

87

COUNTRY/DATE OF RESULTS OF SURVEY PROPOSED/SET DRLs

PUBLICATION

UK 1999

ose‐Width Product:D

ose Width Product

he Dose Area Product (DAP) is directly correlated to the Dose Width Product (DWP),

t of DWP and slit length.

ture of the imaging process and the

narrow width of the x ray beam. The dose quantity used is the product of the absorbed

oduct of the peak dose at the

centre of the x ray beam and the width of the beam, or from an incremental summation

D

T

since DAP is the produc

As it has been already mentioned, the assessment of patient dose in panoramic

radiography is difficult because of the dynamic na

dose in air and the horizontal width of the beam, both measured at the front side of the

secondary collimator slit and integrated over a standard exposure cycle. This is referred

to as Dose Width Product (DWP) with units of mGy mm.

The DWP provides a measurement related to the total amount of radiation to which the

patient is exposed. It can be derived either from the pr

of the dose across the beam. According to P. Doyle’s et al report in 2006, the main dos

measurement techniques, in terms of DWP, are:

‐ Mean 57.4 mGy

mm ‐ Range 1.7‐328

mGy mm

66.7 MGy mm

Dose‐Width Product: ‐ 65mGy mm

‐ Third Quartile

UK 2000

DAP: ‐ Mean 11.3 cGy

cm2 Dose‐Width Product:

‐ Mean 65.2 mGy mm

‐ Third Quartile 75.8 mGy mm

Table 6: European Commission’s Radiation Protection Guidelines in Dental Radiology No

136 (2004), indicative dose values and DRLs, for four European countries.

88

1) “In Beam” Detector and Film

2) Partial Volume Detector (proposed by the authors)

3) TLD Array

When a panoramic x ray unit is installed, radiological parameters (tube potential and

are adjusted so that the density on the resultant film is optimized. This

adjustment is dependent on the sensitivity or speed of the film‐screen combination and

DAP and Effective Dose

In medical radiology, including panoramic x ray imaging, DAP can be converted to

te‐Carlo‐generated conversion factors. DAP can also be used

in dental radiology for the assessment of E without the need for extensive phantom

rmined conversion factor. Poppe et al. (2006) calculated the effective doses E

from the DAP and consequent DRLs’ (by the 75th percentile) results of their survey, using

from a research based in Athens, Greece in

order to create a background of DAP reference levels for future studies, in Greece.

tube current)

the effect of such an adjustment will be reflected in changes in DWP. This parameter is

therefore a useful quality control tool but is not directly related to patient risk. A more

useful parameter for this is the dose area product.

effective dose E using Mon

studies.

The calculation of the effective dose can be carried out by multiplying the DAP with a

pre‐dete

three conversion factors, found in literature.

The same calculations of effective doses E will take place in the 2nd part of this thesis,

according to the results of Tierris et al (2004)

89

J. – S. Lee et al (2010) have summarized the DAP and DWP reference levels from a

number of well established surveys globally, including their own results. A very

tive table is demonstrated below, taken from this survey.

Survey Number of x ray units

Gender/ Age/ Size

DWP (mGy mm) DAP (mGy cm2)

indica

Mean 3rd Quartile Mean 3rd Quartile

Napier (UK) 387 57 67

16 Wi dlliams an Montgomery

(UK) 65 76 113 139

Isoardi and Ropolo (Italy) 5 Adult 74 84

Tierris et al. (Greece)

101 117 Male 62 Female 85 97

Child 68 77

H2175 (DWP) 1910 (DAP)

Ad d 60 art and Wall

(UK)

ult anChild

82

Doyle e a . t l(UK) 20 65 67 89 90

Poppe e al. Lar lt 8 101.4

t (Germany) 50

ge Adu 5.7Male 76.4 87 Female 7 8 1.6 4.4Child 59.3 75.4

Kim et l. 36 72.1 106.7 a (Korea) Adult

Lee et al. 44 Adult 47.7 60.1

(Korea)

Table 6: DR DAP in pan radiol et al 2010).

Ls (from and DWP) oramic ogy (Lee

90

91

lthough the differences between the values of the same parameters may seem quite

large, it should be mentioned that despite the fact that the parameters are the same

, DWP), the methods used for their calculation, as well as the number of panoramic

A

(DAP

x ray units used in each survey, differ from one report to another. This table is indicative

of the range of these values, but if a long‐term study from different authors is to be

made in order to achieve some useful DRLs, this should be executed in one country (or

more but without significant or determining variations in populations’ characteristics)

with some standard and commonly recognized methods and a minimum number of

panoramic x ray units needed for each survey.

CHAPTER 5

QUALITY CONTROL PROTOCOLS

CODES OF PRACTICE – LEGISLATION

INTRODUCTION

In this chapter a short presentation of Quality Control references will be presented,

concerning dental x ray panoramic imaging.

1) Greek Atomic Energy Commission – Protocol of Periodical Quality Control Checks on

Orthopantograph, October 2006

The protocol of the Greek Atomic Energy Commission focuses on the proper

functionality of the panoramic unit exclusively. On these terms it supplies a typical yet

substantial quality control upon the modalities.

While it is mentioned that all supply, HVL and repeatability checks (including time) are

the same as the basic QC checks of conventional radiographic systems, the protocol

determines the quality controlling of movement, image quality, field size, radiation

dose, FSD and correspondence of radiation field with the alignment slit of the cassette.

Taking into consideration the complexity and the difficulty of the technique, the

frequency of QC checks could be considered as an expanded one.

92

PROTOCOL OF PERIODICAL QUALITY CONTROL CHECKS FOR ORTHOPANTOMOGRAPHS

Parameter Parameter procedure Test Objects

Test Voltage

Accepted Limits

Frequency of Quality Control Check

KVp accuracy and repeatability checks (*), supply, HVL and exposure time repeatability checks are the same with t cks of entional radiographic systems. he basic quality control che conv

Correspondence of radiation field

with the alignment slit of the radiographic

cassette

Check of correspondence of radiation field with the alignment slit of the radiographic cassette

Film

Annually

Movement

Rotation of the tubecassette

system

Check and confirmation

of proper movement/rotation of tube‐cassette system

Annually

Image Quality Check of the quality of received images

Film Annually

Field Size

Measurement of the field diameter on the outer extremity of the beam

applier

Film and Led

Markers

≤ 150x10 mm in t he slot

Annually

Radiation Supply

Measurement of the radiation supply

Proper Dosimeter

50‐70 KVp with 1 m

distance from the radiant

30‐80 mGy/ mAs

Annually

Focal to Skin Distance (FSD)

Tapeline ≥ 30 cm

*The supply in panoramic systems is measured with DAP or with pencil beam dosimeters.

Requirements for Dental Panoramic and Cephalometric Examinations, by the GAEC.

‐ All units must satisfy the requirements of the regulations that are mentioned at

the department of medical radio‐diagnostic machines. Moreover the following

must be effective:

‐ The units must function with high voltage of at least 60 – 90 kVp, while the

minimum filter that interferes to the used beam must be 2.5mm Al.

‐ Specialized systems and equipment of head holding and immobilizing must be

present.

93

‐ During panoramic examinations, the dimensions of the radiation field upon the

film holder must not exceed the 10 mm x 150 mm.

‐ The use of endodentulous tubes for panoramic or simple radiographs is

prohibited.

2) Conference of Radiation Control Program Directors, Inc – Quality Control

Recommendations for Diagnostic Radiography, Volume 1, Dental Facilities, July 2001

This general and integrated Quality Control Program concerns all facilities using dental

intraoral, panoramic or cephalometric x ray units. Although it corresponds mainly to the

employees of such facilities and secondly to QA experts, this Protocol succeeds in

introducing a well based overall quality check of the whole laboratory, including the x

ray panoramic unit. The frequency of the tests is well established according to the

needs. The following table is indicative of the information contained in this Program.

Recommended Quality Control Tests for Dental Facilities

TEST FREQUENCY PROCEDURE Dental System Constancy Test (Intraoral Only)

Daily, Prior to Developing Films and After Service

1

Processor QC (Extraoral) Daily, Prior to Developing Films 2, Appendix B Darkroom QC Daily and Weekly 3 View boxes Monthly 4 Visual Checklist Quarterly and After Service 5 Repeat Analysis Quarterly 6 Tube Head – Boom Stability

Quarterly 7

Film and Chemical Storage Quarterly 8 Cassettes and Screens Quarterly or Semiannually(as

needed) 9

Darkroom Fog Semiannually* 10A or 10B Lead Apron Check Annually 11 Panoramic Field Alignment Annually 12 Program Review Annually Form 6 Radiation Safety Survey Every Two Year Form 4 * Darkroom fog should beevaluated every time you change the filter, bulb or ilm type and at least every 6 months.

94

3) European Commission – Radiation Protection 136‐ European Guidelines Radiation

Protection in Dental Radiology, 2004

The European Commission Guidelines mainly concern the users of the modalities. On

these terms the x ray unit Quality Controlling lacks of detailed guideline and

information. However, this Quality Assurance Protocol gives a well established general

idea concerning the appropriate procedures that all practitioners should consider. The

following table demonstrates some quality assurance information considering

panoramic radiography.

Quality Standards for Panoramic Radiography

Patient preparation / instruction adequate ‐ Edge to edge incisor

‐

s ‐ bodies (e.g. earrings, spectacles, dentures) No removable metallic foreign

‐ No motion artefacts Tongue against roof of mouth

‐ Minimisation of spine shadow

No patient positioning errors ‐ No antero‐posterior positioning errors (equal vertical and horizontal

magnification) ‐ ors (symmetrical magnification) No mid sagittal plane positioning err‐ No occlusal plane positioning errors ‐ Correct positioning of spinal column

Correct anatomical coverage

‐ Appropriate coverage depending upon the clinical application. Field size limitation should have been used (if available) to exclude structures irrelevant to clinical needs (e.g. limitation of field to teeth and alveolar bone for everyday dental use)

Good density and contrast

‐ There should be good density and adequate contrast between the enamel and the dentine

No cassette / screen problems

‐ No lights leaksGood film / sc

‐ Clean screens

‐ reen contact

Adequate processing and darkroom techniques

‐ atches No pressure marks on film, mo emulsion scr‐ No roller marks (automatic processing only ‐ No evidence of film fog ‐ n No chemical streaks / splashes / contaminatio‐ g No evidence of inadequate fixation / washin‐ Name / date / left or right marker all legible

95

4) International Atomic Energy Agency – Dosimetry in Diagnostic Radiology: An

International Code of Practice (Technical Reports Series No. 457), Vienna, 2007

As entitled, this fully detailed protocol concerns dosimetric procedures for all medical x

ray techniques. On this basis, the dosimetric one, this scientific code of practice contains

integrated and important theoretical and practical information about dosimetric quality

control. In the previous chapter the methods and the worksheets of this protocol

concerning panoramic imaging were demonstrated.

5) Health Canada – Radiation Protection in Dentistry, Recommended Safety

Procedures for the Use of Dental x ray Equipment, Safety Code30, 2000

This Code of Practice, published by the Canadian Health Ministry, contains a full

guideline of Quality Control Assurance of the whole dental x ray laboratory. Personnel

guidelines, facilities requirements, equipment specifications, film and processing

handling, Quality Assurance Program, Radiation Reduce and proper shielding are some

of the main contents of this well based protocol. The following table demonstrates the

Quality Control Program for Dental Radiography, including panoramic imaging.

Essential Dental Radiography Quality Control

Test Performance Criteria Minimum Frequency Test Film and Film

Processing ± 1 step (stepwedge) < ± 0.1 optical density

Daily

Test Radiogram Visual Daily Retake Record Visual Daily

Operation of Darkroom Visual Quarterly Cassettes and Screens Visual Annually

Filtration (Reference) Annually and After Service Controlling Timer (Reference) Annually and After Service

X ray Tube Shielding (Reference) Annually ad After X ray Tube Housing Service

X ray Tube Voltage (Reference) Annually and After Service Irradiation Switch (Reference) Annually and After Service

Focal Spot to Skin Distance (Reference) Annually and After Service Beam Alignment and

Collimation (Reference) Annually and After Service

Patient Radiation Dose (Reference) Annually and After Service

96

6) Care Quality Commission ‐ The Ionizing Radiation (Medical Exposure) Regulations,

Great Britain, 2006

This Protocol stands mostly for the determination of the legitimacy code concerning

medial exposures. On this basis, it information is general and representative rather than

mainly scientific and technically. However, this Protocol clarifies a clear spectrum of the

medical x ray techniques, so that a responsible application can be made. This protocol

creates an appropriate basis for well established Quality Control Programs.

7) Greek Ministry of Health, Greek Regulations for Radiation Protection, 2001.

The Greek Radiation Protection Regulation clarifies the legitimate basis, on the grounds

of which Quality Assurance Programs can be developed.

97

SECTION II

EXPERIMENTAL PART

99

CHAPTER 6

CALCULATION OF THE EFFECTIVE DOSE (E), USING THE DRLs of TIERRIS ET AL. (2004)

INTRODUCTION

In this section, a calculation of the effective dose E will be carried out, from the results

of the research of Tierris et al (2004). Effective dose E can be calculated by multiplying

the DAP with a pre‐determined conversion factor.

,

METHOD

Three conversion factors will be used from literature according to the survey of Poppe et

al (2006). This survey used these 3 factors for the determination of effective dose E

according to the DAP results of a research on 50 panoramic units of different vendors.

The conversion factors are:

1) Williams and Montgomery‘s (2000) conversion factor of 0.06 mSv Gy‐1 cm‐2

(calculated using the effective dose obtained from literature by White).

2) Helmrot and Alm Carlsson (2002) published a conversion factor including

salivary glands of 0.08 mSv Gy‐1 cm‐2, for panoramic examinations, using a multi‐

material compound hard tissue phantom.

3) Visser (2000) made an extensive study with a specially designed for x ray

energies anthropomorphic tissue‐equivalent phantom and found a conversion

factor of 0.21 mSv Gy‐1 cm‐2.

Compared with the E,DAP conversion factors by Williams and Montgomery, and Helmrot

and Carlsson, Visser’s factor differs by a factor of 3.5 and 2.6 respectively. The

discrepancy of the conversion factors may result from the different measuring

techniques used and different calculation schemes adopted when calculating effective

doses. Lecomber et al (2000) have shown that the salivary gland is exposed to high doses

101

in dental panoramic radiology and its inclusion in the list of remainder organs when

calculating effective dose has been questioned. Poppe et al. (2006) mark that the

effective dose calculated using the conversion factor from Visser (2000) shows that the

risk associated with a panoramic radiography is equivalent to a chest examination.

Therefore, the suggestion is to take the values derived by Visser (2000) as an upper dose

limit as his study has been carried out under extensive consideration in order to most

closely resemble the realistic conditions of application in dental procedures.

Tierris et al (2004), measured ‐in real time patient examinations‐ DAP values in 62

panoramic x ray units of the private and public sector in Athens, Greece, with the use of

a DAP meter, in order to determine corresponding DRLs. The results are shown on the

following table:

Exposure Mean (kV)

Mean (mA)

Mean Exposure Time (s)

Mean DAP (mGy cm2)

DAP Reference Levels (3rd Quartile) (mGy cm2)

Male 72.4 10.5 15.2 101 117 Female 68.3 10.1 14.9 85 97 Child 64.3 9.7 14.8 68 77 Table 1: Mean exposures parameters for 3 different exposure types, mean measured DAP and DAP

reference levels in 62 panoramic x ray units, by Tierris et al (2004).

CALCULATION

The calculation of the effective dose E now will take place, multiplying the DAP

Reference Levels of Tierris et al. (2004) with each conversion factor shown above. The

results are demo llowing table. nstrated in the fo

Exposure

DAP Reference Levels (mGy cm2) Effe (μSctive Dose E v)

Williams and Montgomery

Helmrot and Carlsson

Visser

Male 117 7.02 9.36 24.57 Female 97 5.82 7.76 20.37 Child 77 4.62 6.16 16.17

Table 2: Calculation of Effective Dose (E), using DRLs from Tierris et al, multiplied by three different conversion factors found in literature (Poppe et al., 2006)

102

103

CONCLUSION

The values in the table above are remarkably higher than the respective values of Poppe

et al. (2006). Indeed, their higher than most results on the surveys mentioned on

Chapter 4. This may be a result from the fact that 8 x ray units from the survey of Tierris

et al. (2004) gave significantly high DAP values compared to the high DAP values of other

researchers. Excluding the 8 highest DAP doses from each research, it is noticeable that

the values lie in the same range. According to Poppe et al.(2006) it would be appropriate

to consider the values derived from Visser (2000) as an upper dose limit.

CHAPTER 7

QUALITY CONTROL OF

A PANORAMIC – CEPHALOMETRIC UNIT

(INSTRUMENTARIUM OC/OD-200D)

A.1 LABORATORY DESCRIPTION – EQUIPMENT RECORD

A.1.1 Equipment Description

The type of the machine as well as its apparatus along with the specifications of its

partial segments, have been recorded. Particularly:

Generator

The power supply generator of the tube is made by TOSHIBA Company.

Generator

Voltage : 57‐85 kVp

Current : 20 – 16 mA

Time : 2.7 – 17.6 s (panoramic), 5 – 20 s (cephalometric)

Filter : 2.5 mm Al

Focal Spot Size : 0.5 x 0.5 mm

CE Mark : OK Table 1: Generator Specifications.

Digital Detector

Type : Charged Coupled Device (CCD)

Sensor Pixel Size : 48 x 48 μm

Image Pixel Size : 96 x 96 μm

Image Field Height : 147 mm – 221 mm

Resolution : 5.5 lp/mm

CE Mark : OK Table 2: Digital Detector Specifications.

104

Bo

sy

im

45

oth modes o

ystem uses d

mages are p

500M).

f the unit, pa

igital detect

rinted in fil

anoramic an

ors (CCD) it

ms by a dig

d cephalome

is connected

gital thermo

etric, functio

d with a wor

o‐printer (Dic

on in fan bea

kstation com

com Printer

Picture 1: Panoramic – COC/O

Picture 2: W

105

Cephalometric OD‐200D, Tosh

Workstation an

Unit, Instrumehiba

am field. As t

mputer and t

r, Agfa Dryst

the

the

tar

entarium

nd Digital Printeer.

A.1.2 Ventilation – Air Condition – Illumination

nd air‐condition of the laboratory were

FUNCTIONALITY

The details concerning illumination, ventilation a

recorded. Their appropriateness was evaluated so that the optimal functional conditions

of the units, as well as the personnel working conditions and the comfort of the

examinees, are ensured.

SYSTEM Ventilation Excellent Air‐condition Excellent Illumination Excellent Notes: The illumination and the ventilation of tory are mainly artificial. the labora

Table 3: Ventilation, Air‐conditio ation Conditions.

n and Illumin

106

A.2. CONTROLS

A.2.1. General Apparatus Controls

A.2.1.1. Inspectional Control of the Unit Components

The task of this control is the contribution to the assurance of the mechanical and

electrical function of the x ray system. For this reason the motion of the tube was

checked (visually and acoustically). The movements and the mechanical condition of all

the partial systems were checked. The function of the illuminating display signs on the

console was checked. Finally, the physical condition of the cables was checked.

CONTROL RESULT Tube Motion Excellent Movement/Rotation of tube‐detector system Excellent Physical Condition of cables Excellent

Table 4: Inspectional Control of the Unit Components.

A.2.1.2. Optical and Acoustic Communication between Examiner‐Examinee

Concerning the confirmation of the optimal inspection upon the examinee, the

appropriate acoustic communication, as well as the appropriate optical contact between

the examiner and the examinee, were checked.

CONTROL RESULT Audio Communication System No intercom present Optical contact examiner‐examinee Excellent (by lead‐glass window)

Table 5: Audio‐Optical Control.

A.2.1.3. Presence of Technical Manuals and Maintenace/Functioning Log‐Book

CONTROL RESULT User Manuals Present Reference Manuals Present

Table 6: Documentation Control.

107

A.2.2. Radioprotection Control

A.2.2.1. Spatial Characterization – Chamber Signage

Control Result Controlled Areas Record System Chamber Superintended Areas Record Controlling (Consoling) Space Non‐controlled (Public) Areas Record Patient Lounge Chamber,

Dentistry Space, Doctor’s Office Presence of Warning Signs Yes Presence of Optical and Audio Sign during Exposures

Yes

Notes: Table 7: Spatial‐Chamber Control.

A.2.2.2. Verification of Radioprotection Report – Shield Control

For the transaction of the control measurements an x ray dose rate meter was used

(Survey‐Meter, Inovision 451P) with a minimum measurement capability of 0.001 μSv/h.

The shielding for the primary as well as the secondary (scattered) radiation was checked.

It was also checked whether the shielding is constant, sufficiently covering the door

frames and whether a lead incrustation is present in the monitoring (consoling) window.

Moreover, a dose rate measurement was taken upon the interfaces of the space.

Control Result Presence of Radioprotection Report Yes (by Radiophysicists H. Delis – S.

Skiadopoulos, April 2007 Workload (mAmin/week) According to the Radioprotection

Report, 210 mAmin/week Control of Shielding Constancy Acceptable (No inconstancies from the

measurements on the shielded interfaces)

Control of lead‐glass in the monitoring window

Physical Condition: Excellent

Table 8: Radioprotection Report‐ Shield Control.

108

Dose Rate Measurements in Neighboring Spaces Measurement

High Voltage (kVp): 57 Tube Current (mA): 2

Time (s): 17.6

Dose Rate (μSv/mAh) Spatial Characterization

Console Chamber Door Mount Superintended Areas (1 μSv/hr for 1mA tube

current) Monitoring Window 0.23

Toilet (WC) 0.05 Public Areas (0.1 μSv/hr for 1mA tube current) Waiting Room Mount

Table 9: Dose Rate Measurements in Neighboring Spaces.

The system functions in fan beam field (both for panoramic and cephalometric modes),

approximately 147 x 3 mm for panoramic mode and 221 x 3 mm for cephalometric

mode.

A.2.2.3. Record and Control of Physical Condition of Radioprotection Apparatus

Concerning the protection of the laboratory personnel, the public and the examinees

from causeless exposure on x ray, the laboratory has been supplied with the following

radioprotection apparatus for the personnel and examinees:

‐ One (1) full‐body protective apron of equivalent thickness 0.30 mm Pb.

‐ One (1) full‐body protective apron with a protective thyroid collar of equivalent

thickness 0.30 mm Pb.

A.2.2.4. Tube Head Escape

Measurements of exposure rate were made, in 1m distance, with an appropriate x ray

dosimeter, calibrated at energies 20‐150 keV, with minimum measurement capability

0.01 μSv/h. The maximum exposure rate measured was 0.08 mSv/h in 1m distance

(acceptance limit: 1 mSv/h in 1m distance).

109

A.2.3. Beam Geometry Control

A.2.3.1. Conjunction of Radiation Field with the Alignment Slit of the Digital Detector

For this control, a radiotherapy film was used, positioned in front of alignment slit. Upon

the film the position of the slit was marked. The total conjunction between the radiation

field and alignment slit of the digital detector was confirmed.

The system functions in fan beam field (both for panoramic and cephalometric modes),

approximately 147 x 3 mm for panoramic mode and 221 x 3 mm for cephalometric

mode.

A.2.3.2. Measurement of Minimum Distance Focus‐Examinee

With a direct measurement the distance Focus‐Examinee was determined

(approximately 18cm for panoramic mode and more than 1 m (approximately 1.4 m) for

cephalometric mode.

A.2.3.3. FFD Control

The FFD (Focus‐to‐Detector Distance), as mentioned in the technical manuals of the

unit, is 487 mm for panoramic mode and 1600 mm for cephalometric.

110

A.2.4. Beam Quality Control

A.2.4.1. Accuracy of High Voltage Values

For this specific control an electronic meter was used (Victoreen, x ray test device,

Model 4000M+ ‐ SI). Five (5) high voltage values were measured for various options of

charge (cephalometric mode). The results are listed in the following table.

Nominal High Voltage Value (kVp)

Charge (mAs)

Measured High Voltage Value (kVp)

Deflection (%)

60 12.0 58.92 1.80 60 16.0 58.76 2.07 60 20.0 58.12 3.13 66 12.0 65.07 1.41 66 16.0 64.80 1.82 66 20.0 64.64 2.06 70 12.0 70.03 ‐0.04 70 16.0 69.81 0.27 70 20.0 69.84 0.23 76 12.0 76.67 ‐0.88 76 16.0 76.64 ‐0.84 76 20.0 76.21 ‐0.28 80 19.2 80.15 ‐0.19 80 19.2 80.22 ‐0.27 80 19.2 79.91 0.11 80 9.6 80.24 ‐0.30 80 4.8 80.23 ‐0.29 80 36.0 80.45 ‐0.56 80 24.0 80.01 ‐0.01 80 8.0 80.11 ‐0.14 80 12.0 80.63 ‐0.79 80 16.0 80.63 ‐0.79 80 20.0 80.32 ‐0.40

Table 10: Accuracy of High Voltage Values Control.

The deflections listed above are acceptable, as the maximum acceptance limit 10% of

the nominal high voltage values. The maximum deflection of the measured high voltage

values is 3.13%.

±

111

A.2.4.2. Repeatability of High Voltage Values

For nominal high voltage value 80 kVp and charge 19.2 mAs, five (5) high voltage values

were measured (cephalometric mode). The results of the measurements are listed in the

table below:

Nominal High Voltage Value

(kVp)

Charge (mAs)

Measured High Voltage Value (kVp)

Repeatability (%)

80 19.2

80.15

0.17 80.22 79.91 80.24 80.23

Note: For repeatability the coefficient of variation is used. Table 11: Repeatability of High Voltrage Values Control.

From the analysis, the repeatability of the high voltage values is 0.17%. This value is

acceptable, as the maximum limit of acceptance is ± 5%.

112

A.2.4.3. Half Value Layer (HVL) of the beam – Tube Total Filtering

For this control a pencil shaped dosimeter was used along with a multimeter

(Victoreen). The dosimeter was placed in parallel with the slit.

For the calculation of the HVL different aluminum pieces of increasing thicknesses were

used. The measurements are shown in the table below.

Table 12: Half Value Layer Estimation.

The HVL that comes from the measurements above is HVL=3.0 mm Al. From the

following curve it comes that the total filtering of the tube is approximately 3.1 mm Al,

with a minimum acceptance limit of 2.5 mm Al. Thus, the total filtering of the tube is

inside the acceptance limits.

Thickness Al (mm)

0.00 0.33 1.00 2.30 3.30

Dose (%) 100.0 90.59 77.73 59.47 46.47

113

A.2.5. Beam Quantity Control

A.2.5.1. Timer Accuracy

For this specific control an electronic meter was used (Victoreen, x ray device, Model

4000M+ ‐ SI). Six (6) time values were measured (in cephalometric mode) for various

current options. The results of the measurements are listed in the following table.

Nominal Time Value (s) Measured Time Value (s) Deflection (%) 1.0 0.9967 0.33 1.6 1.5970 0.19 2.0 1.9980 0.10 1.0 0.9991 0.09 1.6 1.6010 ‐0.06 2.0 2.0020 ‐0.10 1.0 0.9998 ‐.02 1.6 1.6020 ‐0.13 2.0 2.0030 ‐0.15 1.0 0.9995 0.05 1.0 1.6030 ‐0.19 2.0 2.0020 ‐0.10 1.6 1.6030 ‐0.19 1.6 1.6030 ‐0.19 1.6 1.6030 ‐0.19 0.8 0.7999 0.01 0.4 0.3987 0.33 3.0 3.0070 ‐0.23 2.0 2.0040 ‐0.20 2.0 2.0030 ‐0.15 2.0 2.0030 ‐0.15 2.0 2.0030 ‐0.15 2.0 2.0030 ‐0.15

Table 13: Timer Accuracy Control.

From the analysis it comes that for all the used current options the highest deflection of

the measured value of the exposure time compared to its nominal value is 0.33%. The

above deflections are acceptable as the maximum limit of acceptance is 10% of the

nominal value of the exposure time for time values >0.1s.

±±

114

A.2.5.2. Timer Repeatability

The table below includes the results of the timer repeatability control for two (2) values

of the exposure time (cephalometric mode).

Nominal Time Value (s) Measured Time Value (s) Repeatability (%)

1.6

1.5970

0.146

1.6010 1.6020 1.6030 1.6030 1.6030

2.0

1.9980

0.092

2.0020 2.0030 2.0040 2.0030 2.0030 2.0030 2.0030

Table 14: Timer Repeatability Control.

The minimum repeatability is 0.146%, which is included in the acceptance limits

(acceptance limit: ± 5%).

A.2.5.3. Tube Supply Linearity and Repeatability

For this control a pencil shaped dosimeter was used along with a multimeter

(Victoreen). The dosimeter was placed in parallel with the slit and the necessary

corrections were made concerning the calibration coefficient of the dosimeter and the

active magnitude of the dosimeter in relation to the radiation field, while a reduction of

the values was made for 100 cm distance.

For most used current values (mA) and for high voltage 80 kVp, the absorbed dose

(mGy) in the panoramic system was measured for functional time 17.6 s. For the

nominal values of kVp and mAs the supply was calculated in μGy/mAs in 1 m distance.

The linearity was calculated according to the equation:

115

The measurements are listed in the following table:

High Voltage (kVp) Current (mA) Supply (μGy/mAs) Linearity (%)

80

4 42.33

8.6 5 41.95 8 40.03 10 44.02 13 47.61

Table 15: Tube Supply Linearity Control.

High Voltage (kVp) Current (mA) Supply (μGy/mAs) Repeatability (%)

80 8

40.03

1.2 40.06 39.42 39.98

Table 16: Tube Supply Repeatability Control.

The minimum radiation supply is 39.42 μGy/mAs in 100 cm distance and 80 kVp voltage.

The current linearity of the tube is 8.6% (for various mA, 15% limit) while the

repeatability of the supply is 1.2% (with constant mA) with 5% limit. Thus, the current

linearity and the repeatability of the supply are within the acceptance limits.

A.2.6. Automatic Exposure Selection System

The density scale calibration was checked depending on the tube current and the Dose‐

Area‐Product (DAP). The results are shown in the following curves for high voltage 66

kVp.

The relation between the density scale and the charge, as well as the equivalent

between the density scale and the DAP are depicted in the following graphs.

116

Graph 1: Density scale and charge relation.

Graph 2: Density Scale and DAP relation.

117

A.2.7. Typical Patient Doses

According to the manufacturing company and as the unit functions in fan beam field, the

doses of the patients during the exposures of the examinations are relatively low.

Indicative dose values for panoramic examinations are demonstrated in the following

table.

High Voltage (kV) Current (mA) Dose (μSv) 57 2 1.90 63 10 10.9 66 13 16.8 70 13 20.4 73 8 15.5 77 8 18.7 81 13 31.3 85 13 36.0

Table 17: Typical Patient Doses Estimation.

For cephalometric examinations with high voltage 85 kV and current 13 mA, as the

manufacturing company proposes, the dose values in relation to the time for profile and

anteroposterior projection are demonstrated in the following table.

Time (s) 8 10 16 20 Dose (μSv) 2.7 3.4 5.4 6.8

Table 18: Dose Values in relation to Exposure Time.

A.2.8. Image Quality Control

Using the auto‐control quality system of the unit, which radiates a field with 15 levels of

increasing density, with voltage 57 kV and current 2 mA, the attached film was produced

and the presence of 15 density levels was confirmed, as indicated by the system

manuals.

118

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APPENDIX I

THE DIAGNOSTIC VALUE OF

THE PANORAMIC RADIOGRAPH

A CRITICAL VIEW

THE POPULARITY OF PANORAMIC IMAGING

The use of radiographic systems has become an inextricable procedure of the western

medicine. If in the second half of the 20th century the radiographic units were rising their

popularity, becoming a must tool on the various diagnostic fields of the modern medical

practice, in the beginning of the 21st century their presence has been coincided with the

term of diagnosis itself.

Yet, the question of whether this use is following an appropriate handling is a

fundamental issue of the scientific debate. Along with the uprising of the use of x‐ray

imaging comes the increase of the radiation doses, concerning not only the patient, but

also the professionals involved in these procedures, as well as the general public. More

than ever, the issue of using x‐ray techniques as an inevitable and necessary diagnostic

tool among the others is becoming of the highest importance.

While the dental radiographic techniques import relative doses of the lowest levels,

their extensive use is positioning them very high in hierarchy of the most frequent

radiographic techniques in general. Thus, the high radiation doses which are induced by

dental radiographic systems are indicating that a potential misuse is a fact. A misuse

that concerns the correct use of such units by the professional stuff, a proper form of

selection criteria and the quality of the existing and functioning dental radiographic

units.

Panoramic radiographic units meet a high popularity in dental medicine. Various

scientific estimations report that every year, in the developed countries, millions of

panoramic radiographies are taking place and thousands of panoramic units are installed

and functioning.

(see rushton biblio)Older researches have estimated the numbers of panoramic units

and radiographies in western countries. In the middle of the 90’s, in the UK, there were

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approximately 3250 panoramic x‐ray units and around 1.5 million of panoramic

radiographies were taken annually. In France, while the proportion of dental

radiography made up by panoramic examinations is less than in the UK, the number of

panoramic films taken exceeds that of the UK, reaching a number of 1.7 million. This

means a greater use of radiography of all kinds, as in France most of the panoramic

exposures are carries out by radiologists. In the US, during the 80’s more than 25000

panoramic x‐ray units were used with an extensive rate of usage. In Australia, in 1988,

6% of practitioners used panoramic radiography.

In Greece, the Greek Atomic Energy Commission (GAEC) ‐instituted as the national

competent authority responsible for nuclear safety and radiation protection issues‐

reports that there are 10.000 dental radiographic units installed, authorized and

licensed for use. Among them the number of panoramic units is respectfully high.

These figures obviously underestimate the true scale of use of panoramic radiology, as

films produced in private practice, hospitals and within the community dental services

are not included.

THE QUALITY OF THE PANORAMIC IMAGES

Consequently, the crucial question of whether this extended use of panoramic imaging

is properly justified remains. Although a panoramic radiograph includes an important

substance of information, it is important to realize whether this information itself is

essential for oral diagnose and treatment.

A combination of factors in panoramic radiology which reduce its diagnostic quality

should be taken into consideration by all physicians. These factors are:

‐ The limitations imposed by the film/screen/cassette combination

‐ Tomographic blur

‐ Super‐imposed tissue and “ghost” shadows

‐ The overlap of adjacent teeth

‐ Variations in magnification

Panoramic radiology, being a modified form of tomography, blurs the images of

anatomical structures above and below the “in‐focus” layer, which ranges from 4.5 to 12

mm in the anterior regions and is two or three times greater in the molar regions. In this

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way, the transfer of information from the attenuated x‐ray beam to intensifying screens

and then to the film, inevitably degrades this information.

This degradation is increasing to a variable degree by shadows of soft tissues and

surrounding air. “Ghost” images of the spine and the mandible reduce the diagnostic

quality and the presence of air between the dorsum and the hard palate leads to a band

of relative overexposure of the roots of the maxillary teeth and alveolar bone. Variations

in the horizontal angle of the slit x‐ray beam and the line of the dental arches result in

some amount of overlap of contact points of teeth, particularly in the premolar regions.

To continue with, in panoramic radiography there is a magnification factor from 10% to

30%. However, the degree of horizontal magnification varies considerably, depending

upon the relationship of the structure to the image layer. Thus, inaccuracies in patient

positioning lead to discrepancies between vertical and horizontal magnification of teeth,

with consequent distortion of shape.

As a conclusion, the quality of any radiograph is dependent upon accurate technique

(including the quality of the x‐ray unit) and careful processing. Panoramic radiography

poses particular challenges in both of these aspects of image production. Accurate

positioning and preparation of patients is needed to ensure the image is not distorted or

affected by ghost images, while quality control is critical when screen film is processed.

TECHNICAL AND PROCESSING FAULTS AFFECTING THE IMAGE QUALITY

In 1999, Rushton, Horner and Worthington concluded that the quality of panoramic

radiographs was considerably lower than standards recently set back then for primary

dental care. However, the quality of panoramic radiography could be improved by

careful attention to radiographic technique and processing.

In a study, including 41 dentists and a total of 1,813 panoramic radiographs, only 0.8% o

radiographs were free of faults, while 66.2% were diagnostically acceptable (containing

errors which did not detract from the diagnostic utility and 33.0% were unacceptable.

When all 1,813 radiographs were considered, the mean number of technical faults per

radiograph was 2.75 (SD=1.48). The mean number of processing faults per radiograph

was 2.96 (SD=1.55).

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Faults n % Tongue not in contact with palate 1,298 71.6 Antero‐posterior positioning errors 1,066 58.8 Absence of orientation (left/right) markers 642 35.4 Occlusal plane errors 568 3.3 Incorrect sagittal plane 508 28.0 Slumped position 267 14.7 Foreign objects/ghost shadows 164 9.0 Lower border of mandible off film 164 9.0 Poor film/screen contact 60 3.3 Overlap of upper and lower teeth 56 3.1 Movement artifact 35 2.0

Table 1: Ranking of technical faults observed on the 1,813 radiographs examined in thestudy. n=number of radiographs; %=percentage of radiographs showing the fault. Thepercentages add up more than 100% because most radiographs exhibited more than onetechnical fault (Rushton et al, 1999).

Faults n % Screen artifacts 1,284 70.8 Automatic processors roller marks 752 41.5 Localized film fog 719 39.7 Faults in contrast (too low) 715 39.4 Faults in density (too pale) 659 36.3 Pressure artifacts 377 20.8 Chemical streaks/contamination 271 14.9 Emulsion scratches 248 13.7 Faults in density (too dark) 101 5.6 Generalized film fog 47 2.6 Inadequate fixation/washing 46 2.6 Developer/fixer splashes 16 0.9 Faults in contrast (too high) 6 0.3

Table 2: Ranking of processing faults observed on 1,813 radiographs examined in the study. n = number of radiographs; %=percentage of radiographs showing the fault. The percentages add up to more than 100% as most radiographs exhibit more than one processing fault (Rushton et al, 1999)

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When the 599 (33.0%) unacceptable radiographs were considered in isolation, the mean

number of technical faults per radiograph was 3.54 (SD=147), while the mean number of

processing faults was 3.63 (SD=1.48). The most frequent faults were antero‐posterior

positioning errors and faults in film density and contrast.

Faults n % Antero‐posterior positioning errors

T 324 54.1

Faults in density (too pale) P 241 40.2 Faults in contrast (too low) P 227 37.9 Incorrect sagittal plane T 144 24.0 Occlusal plane errors T 131 21.9 Slumped position T 54 9.0 Screen artifacts P 31 5.2 Generalized film fog P 23 3.8 Foreign objects/ghost shadows T 21 3.5 Localized film fog P 20 3.3 Automatic processor roller marks P 12 2.0 Poor film/screen contact T 9 1.5 Tongue not in contact with palate T 5 0.8 Patient movement T 5 0.8 Chemical streaks/contamination P 4 0.7 Developer/fixer splashes P 3 0.5 Inadequate fixation/washing P 3 0.5

Table 3: Ranking of technical (T) and processing (P) faults observed on the 599 inadequate radiographs and which directly contributed to their inadequacy. n=number of radiographs; %=percentage of radiographs showing the fault. The percentage adds up to more than 100% because inadequacy was frequently due to more than one fault (Rushton et al, 1999)

Analysis of variance identified highly significant differences in the numbers of technical

(F=13.72, two degrees of freedom); P < 0.001) and processing (F=12.40, two degrees of

freedom; P < 0.001) faults between the dentists. Similarly, the proportion of

“unacceptable” radiographs varied markedly from dentist to dentist, from 10% to 72%.

The highest proportion of “excellent” radiographs recorded was 11.1% with no other

dentist achieving a figure exceeding 4%.

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On the following table, there are the results of the repeatability assessment by the

observers. Values of k exceeding 0.75 indicate excellent agreement beyond chance,

values between 0.4 and 0.75 indicate fair to good agreement beyond chance, while

values below 0.4 indicate poor agreement.

Fault assessment % Agreement

k

Overall acceptability 91.2 0.79 (0.67 , 0.91) Tongue not in contact with palate 88.0 0.69 (0.55 , 0.84) Antero‐posterior positioning errors 83.2 0.73 (0.63 , 0.83) Absence of orientation (left/right) markers 95.2 0.87 (0.77 , 0.97) Occlusal plane errors 80.8 0.60 (0.46 , 0.74) Incorrect sagittal plane 76.8 0.50 (0.35 , 0.66) Slumped position 87.2 0.57 (0.39 , 0.76) Foreign objects/ghost shadows 99.2 0.93 (0.79 , 1.00) Lower border of mandible off film 100.0 1.00 (1.00 , 1.00) Screen artifacts 79.2 0.56 (0.42 , 0.71) Automatic processor roller marks 70.4 0.41 (0.26 , 0.57) Localized film fog 94.4 0.88 (0.80 , 0.97) Faults in contrast 84.4 0.66 (0.52 , 0.80) Faults in density 81.6 0.64 (0.51 , 0.77) Pressure artifacts 90.4 0.72 (0.58 , 0.87) Chemical streaks/contamination 88.8 0.40 (0.14 , 0.66) Emulsion scratches 99.2 0.97 (0.91 , 1.00)

Table 4: Repeatability of assessments. Percentage agreement between first and second assessments and the kappa statistic (k) are shown. For k values, 95% confidence intervals are shown in brackets (Rushton et al, 1999).

133

FILM FAULT FREQUENCY WITHIN PANORAMIC RADIOGRAPHS

TAKEN IN GENERAL DENTAL PRACTICE.

In a sample of 2,641 panoramic films that were assessed within published studies, the

proportion of unacceptable films and range of faults was 18.2% and 33.0%.

Anterior/Posterior positioning errors 54.1% Faults in density and contrast 13.0% and 40.2% Incorrect sagittal plane 24.0% Occlusal plan errors 21.9% Slumped patient position 9.0% Screen artifacts 5.2% Film fog 3.8% and 7.0% Foreign objects/Ghost Shadows 3.5% Poor film/screen contact 1.5%

TABLE 5: Film fault frequency within panoramic radiographs taken in general practice

(European Commission, 2004)

In another study, performed in Turkey (Akarslan et al, 2003), through a sample of 460

panoramic radiographs, 173 of them, composing a percentage of 37.61%, were found to

have no errors according to the criteria set.

The most common positioning error was found to be a radiolucent area palatoglossal

airspace over the roots of the maxillary teeth (46.3%) due to the patient’s tongue not

being raised against the palate during exposure time (see fig. 1). Superimposition of the

hyoid bone with the body of the mandible (23.6%) and superimposition of the vertebral

column on to the anterior teeth (22.17%) were the next most common errors (see fig. 2

and 3). The least seen positioning errors were the widening of the anterior teeth due to

the patient biting the bite‐block too far back (1.3%) and the vertical overlap of the

anterior teeth due to the patient’s not biting the bite‐block, or not using a bite‐block

during the exposure (2.39%).

134

On the evaluated radiographs, the most frequent technical errors were too high density

(16.52%) and too low density (15.65%), respectively (see fig. 4 and 5). The least common

error was found to be the presence of dirty or bent films (0.21%) (see fig. 6)

Error n (number) %

Shadow of airway above tongue 213 46.30

Superimposition of hyoid bone 121 26.30

Vertebral column superimposed on anterior teeth

102 22.17

Density too high 76 16.52

Density too low 72 15.65

Occlusal plane tipped down 62 13.47

Asymmetrical placement of teeth 53 11.52

Other miscellaneous errors 45 9.78

Occlusal plane tipped up 43 9.34

Film fogged 34 7.39

Blurring of anterior teeth 32 6.95

Stains on film 29 6.30

Superimposition of spine on other structures 26 5.65

Narrowed anterior teeth 26 5.65

Radiopaque artifact 24 5.21

Patient movement 15 3.26

Vertical overlap of anterior teeth 11 2.39

Marks on film 7 1.52

Widening of anterior teeth 6 1.30

Films dirty or bent 1 0.21

Table 6: Frequency of errors at the evaluated panoramic radiographs. Some films had more than one error so the percentages add up to more than 100 percent (Akarslan et al, 2003).

135

Figure 1: Palatoglossal airspace over the roots of the maxillary teeth.

Figure 2: Superimposition of the hyoid bone on the body of the mandible.

Figure 3: Vertebral column superimposed over the anterior teeth.

136

Figure 4: Film density too high.

Figure 5: Film density too low.

Figure 6: Bent film.

137

THE QUESTIONABLE NECESSITY OF THE PANORAMIC RADIOGRAPH

The same scientific team (Rushton et al, 1999) ran a study based on the same samples.

1,818 panoramic radiographs of consecutive patients along with basic patient

information, radiological reports and treatment plans were recruited. 41 general dental

practitioners who routinely took panoramic radiographs of all new adult patients

participated ad were asked to evaluate the radiographic information. The radiographs

were also reported by “experts”) consensus of two dental radiologist).

Radiological findings were recorded from general dental practitioners assessments

(dentist RY), the experts (expert RY), after exclusion of findings that would have been

seen on posterior bitewing radiographs (MRY) and after exclusion of findings of no

relevance to treatment (MRYT). The results were quite indicative of the questionable

use or abuse of the panoramic x‐ray imaging technique that is being reported.

The majority of patients were dentate (61.2%), with 38.3% being partially dentate and

only 0.5% being edentulous patients. There was no significant difference in age profile

between the study sample and the DPB population figures (P = 0.26). Males made up

1.5% of the patients.

The radiological findings between the dentists and the experts varied greatly, as the

following table shows. For some findings the agreement was higher than 90%, but for

the majority of findings the agreement was poor below 70.5% until 37.1%.

138

Dentist Assessment Number (%)

Expert Assessment Number (%)

% Agreement

P

Presence of calculus deposits

849 (46.7) 961 (52.9) 70.5 <0.001

Periodontal bone loss None Early Moderate Advanced

530 (29.2) 673 (37.0) 436 (24.0) 179 (9.8)

785 (43.2) 682 (37.5) 297 (16.3) 53 (3.0)

52.0

<0.001

Total with bone loss 1288 (70.8) 1032 (56.8) Number of carious lesions None 1 2 3 4 5 or more

783 (43.1) 386 (21.2) 219 (12.1) 151 (8.3) 100 (5.5) 179 (9.8)

560 (30.8) 359 (19.7) 290 (16.0) 182 (10.0) 127 (7.0) 299 (16.5)

37.1

<0.001

Total with any lesions 1035 (56.9) 1257 (69.2) Number of periapical lesions None 1 2 3 4 or more

1261 (69.3) 367 (20.2) 130 (7.1) 30 (1.7) 30 (1.7)

1087 (59.8) 420 (23.1) 162 (8.9) 78 (4.3) 70 (3.9)

69.9

<0.001

Total with any lesions 557 (30.7) 730 (40.2) Number of retained roots None 1 2 3 or more

1586 (87.2) 169 (9.3) 33 (1.8) 30 (1.8)

1503 (82.7) 230 (12.7) 45 (2.5) 39 (2.1)

91.3

<0.001

Total with any retained roots

232 (12.8) 314 (17.3)

Presence of unerupted teeth

623 (34.3) 647 (35.6) 95.1 0.01

Pathology of maxillary antra

11 (0.6) 255 (14.0) 86.7 <0.001

Other abnormalities 64 (3.5) 366 (20.1) 80.0 <0.001

Table 6: Radiological findings of the dentists and the experts obtained from the panoramic radiographic of the study patients (n=1,818 for dentists; n=1,817 for experts). Agreement between the two assessments is shown as a percentage. ‘P’ values relate to McNemar X2 tests comparing proportions of cases with findings present or absent for the two assessments (Rushton et al, 1999).

139

The radiological findings after the exclusion of the findings that would have been seen

on posterior bitewing radiographs are demonstrated in the next table. No radiological

findings were recorded on the radiographs of 17.2% of patients.

N )umber (% Number of carious lesions None 1 2 3 4 5 or more

1 ) 401 (77.1 243 (13.4) 96 (5.3) 38 (2.1) 20 (1.1) 19 (1.0)

Total with any lesions 406 (22.9) Number of periapical lesions None 1 2 3 4 or more

1 ) 087 (59.8 420 (23.1)162 (8.9) 78 (4.3) 70 (3.9)

Total with any lesions 730 (40.2) Number of retained roots None 1 2 3 or more

1 503 (82.7) 230 (12.7) 45 (2.5) 39 (2.1)

Total with any retained roots 314 (17.3) Presence of unerupted teeth None 1 or more

1170 ( 4.4) 6 647 (35.6)

Pathology of maxillary antra None Either or both antra

1562 86) ( 255 (14)

Other abnormalities None 1 or more

1451 (80) 366 (20)

Table 7: Radiological findings on the 1,817 panoramic radiographs after exclusion of information that would have been identified on posterior bitewing radiographs (Rushton et al, 1999)

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After the exclusion of findings of no relevance to treatment the results were impressing.

The majority of the radiographs (56.3%) had no radiological findings of relevance to

treatment.

Number (%) of radiographs Number of carious lesions None 1 2 3 4 5 or more

1 567 (86.2)147 (8.1) 53 (2.9) 23 (1.3) 11 (0.6) 15 (0.8)

Total with any lesions 249 (13.8) Number of periapical lesions None 1 2 3 4 or more

1 ) 406 (77.4 2 ) 91 (16.0 85 (4.7) 15 (0.8) 19 (1.1)

Total with any lesions 410 (22.6) Number of retained roots None 1 2 3 or more

1 ) 681 (92.6 94 (5.2) 15 (0.8) 26 (1.4)

Total with any retained roots 135 (7.4) Presence of unerupted teeth 156 (8.6) Pathology of maxillary antra 5 (0.3) Other abnormalities 69 (3.8) Preextraction information 1 ) 89 (10.4Significant negative finding 2 (0.1)

Table 8: Radiological findings of significance to treatment on the 1,816 panoramic radiographic. This excluded information that would have been identified on posterior bitewing radiographs and findings which did not contribute to patient management (Rushton et al, 1999).

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THE PANORAMIC X‐RAY EQUIPMENT AND THE OPERATING PERSONNEL

Moreover, the status of the panoramic x‐ray units plays a crucial role in the diagnostic

value of the radiography. Much of the equipment used is greater than 10 year old.

Taking into consideration the latest 3‐D panoramic technique, there can be a substantial

recession of the panoramic units according to the available technologies, mostly due to

economical reasons, as the financial differences of the latest technologies are very high.

Also, the proper maintenance of the existing units is another crucial point as many of

them lack of proper maintenance also mostly to economical reasons.

Additionally, another factor that reduces the diagnostic value of the panoramic

radiograph is the operation of inexperienced and uneducated stuff. This is reported in

high frequencies in most countries, and especially in those in which the legislation is

looser. Panoramic imaging techniques as mentioned before needs an exacting handling

and the operation by non professionals increases the possibility of positioning errors,

technical or processing faults.

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