Introduction to Positron Emission Tomography -...
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Introduction to Positron Emission Tomography with your host, Terry Oakes Positron Annihilation γ #1 γ #2 180 o T.R.Oakes Univ. WI-Madison
Transcript of Introduction to Positron Emission Tomography -...
Introduction toPositron Emission Tomography
with your host, Terry Oakes
Positron Annihilationγ#1 γ#2
180 o
T.R.OakesUniv. WI-Madison
Positron Annihilation
180 o
positronemittingatom
neighboringatom
Positron range:1-10 mm
Gamma-Ray range:10 mm - 8
positronannihilation
γ#2γ#1
T.R.OakesUniv. WI-Madison
Positron Emission Tomography
detector #2
detector #1
γ#2
γ#1
detectorring
T.R.OakesUniv. WI-Madison
Positron Emission Tomography
detector #1
γ#2
γ#1
detector #2
T.R.OakesUniv. WI-Madison
Positron Emission Tomography
T.R.OakesUniv. WI-Madison
Positron Emission Tomography
T.R.OakesUniv. WI-Madison
Positron Emission Tomography
T.R.OakesUniv. WI-Madison
P.E.T. measures Concentration of Radioactivity
1) Gamma-rays escape from body:External detection possible.
2) Two gamma rays emittedat 180 when a positronannihilates:The annihilation occuredsomewhere between the two detectors.
o
3) Regions with greaterradioactivity levelsproduce more LORs:Concentration of radioactivitycan be measured and quantified.
T.R.OakesUniv. WI-Madison
P.E.T. yields Quantitative results. ( µCi/cc tissue )
Corrections must be applied to raw data:1) Dead-time, Random events2) Calibration3) Normalization4) Scatter-correction5) Attenuation correction6) Reconstruction
T.R.OakesUniv. WI-Madison
Corrections to Sinograms color scale
raw sinogram(20 cm cylinder)
trim(remove edges)
Scatter-Correct
mash(combine angular views)
Normalized,without Scatter-Correction
Normalize
T.R.OakesUniv. WI-Madison
Effect of Corrections on Images
Uniform20 cm cylinder
color scaleT.R.Oakes
Univ. WI-Madison
Scatter-corrected
Normalized
Attenuation-corrected
X
X
X
X
X
X
X
X
X
CalibrationConverting
“counts/pixel”to
“microCi / cc tissue”
detectorring
knownradioactivityconcentration
Measure response ofthe PET scanner to aknown concentrationof radioactivity.
Obtain Calibration Factor
applicable for all scans.( CF ~ (µCi/cc)/counts )
T.R.OakesUniv. WI-Madison
Normalizationdetector
ring
T.R.OakesUniv. WI-Madison
Normalization
Normalization produces auniform response to thesame level of radioactivity.
Individual detectors responddifferently to the same levelof radioactivity.
T.R.OakesUniv. WI-Madison
Attenuation CorrectionGamma-ray attenuation proportional to:1) density of object2) pathlength through object
Attenuation can be corrected with a density-weighted map of the object.
gamma-rayattenuated
rotatingradioactiveline-source
Attenuation causes a non-uniform loss of events; more gamma rays passing through the middle of the object are lost.
T.R.OakesUniv. WI-Madison
Scatter CorrectionScatter tends to increase the concentration measured toward the center of the object.
Scattered gamma rays causerecorded events to be mispositioned.
gamma-ray scattered scattered
events
unscattered(true) events
num
ber o
f eve
nts
T.R.OakesUniv. WI-Madison
radial bin
PET Data Acquistion
raw sinogram
Radioactive sourcein PET scanner
T.R.OakesUniv. WI-Madison
P.E.T. data are acquired as discrete Lines of Response (LORs)
radial binsradial bins
radial bins
Angular View #1(theta = 0)
Angular View #2(theta = 45)
Angular View #3(theta = 90)
T.R.OakesUniv. WI-Madison
Angular View #1(theta = 0)Three Angular Views
Angular View #2(theta = 45)
T.R.OakesUniv. WI-Madison
Angular View #3(theta = 90)
Angular View #2(theta = 45)
T.R.OakesUniv. WI-Madison
Angular View #3(theta = 90)
Angular View #1(theta = 0)
angu
lar
view
sSinogram
#1
#2
#3
radial bins
Image Reconstruction
raw sinogram Reconstructed Image
it’s magic!
T.R.OakesUniv. WI-Madison
