Evaluation of estimated CEM43 values attained for realistic use …€¦ · Johan van den Brink, 28...

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1 Evaluation of estimated CEM43 values attained for realistic use cases under (local) SAR constraints imposed by IEC60601-2-33 Johan van den Brink Principal Scientist MRI 28 May 2015

Transcript of Evaluation of estimated CEM43 values attained for realistic use …€¦ · Johan van den Brink, 28...

Page 1: Evaluation of estimated CEM43 values attained for realistic use …€¦ · Johan van den Brink, 28 May 2015 3 IEC60601-2-33 and SAR safety management •IEC60601-2-33 is a voluntary

1 Johan van den Brink, 28 May 2015

Evaluation of estimated CEM43 values attained for realistic use cases under (local) SAR constraints imposed by IEC60601-2-33

Johan van den Brink Principal Scientist MRI

28 May 2015

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Outline

• Overview of IEC60601-2-33 (Δ)T and SAR limits for patients • Retrospective CEM43 analysis using the Neufeld–Murbach model • Discussion

Acknowledgements: dr Geran Peeren implemented the fast model for data evaluation dr Cecilia Possanzini for helpful discussions

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IEC60601-2-33 and SAR safety management

• IEC60601-2-33 is a voluntary consensus standard to ensure safe operation of MRI • MRI intentionally applies high power RF to generate images • Three operating modes are defined with different safety profiles – Normal operating mode mode of operation in which none of the outputs have a value that may cause

physiological stress to patients – First level controlled operating mode one or more outputs reach a value that may cause physiological stress which

needs to be controlled by medical supervision – Second level controlled operating mode one or more outputs reach a value that may produce significant risk for

patients, for which explicit ethical approval is required

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SAR has been used as surrogate for Temperature

• Whole Body (WB) SAR limits have been successful in preventing thermal damage • Advanced RF modeling revealed higher than expected values for

local SAR (psSAR10g), energy dose and local temperatures • Vendors evaluate local SAR as voluntary control on RF exposures • Is there a need for more advanced measures like deposited energy or CEM43?

In other words: is the concept of exposure duration critical to patient safety?

Normal operating

mode

1st level controlled

operating mode

2nd level controlled

operating mode

RF: SAR limits

- whole body SAR

- head SAR

- local SAR head/trunk

- local SAR extremities

2 W/kg

3.2 W/kg

10 W/kg

20 W/kg

4 W/kg

3.2 W/kg

20 W/kg

40 W/kg

> 4 W/kg

> 3.2 W/kg

> 20W/kg

> 40 W/kg

energy dose 240 W min / kg

1

Normal operating

mode

1st level controlled

operating mode

2nd level controlled

operating mode

RF: SAR limits

- whole body SAR

- head SAR

- local SAR head/trunk

- local SAR extremities

2 W/kg

3.2 W/kg

10 W/kg

20 W/kg

4 W/kg

3.2 W/kg

20 W/kg

40 W/kg

> 4 W/kg

> 3.2 W/kg

> 20W/kg

> 40 W/kg

energy dose 240 W min / kg

IEC 60601-2-33 limit values (edition 3)

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Exposure duration to reach ΔTcore < 0.5°C & < 1.0°C

• Core temperature increase estimated from Adair & Berglund, 1989

• Ta = 25 °C thermoregulatory healthy patient compromised patient uncovered covered uncovered covered

WB SAR

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

tmax (min.)

71.0

53.6

43.0

35.9

30.9

54.1

48.1

43.3

39.4

36.2

33.4

31.0

29.0

27.2

25.6

0.5⁰C

1.0⁰C

tmax (min.)

59.2

41.2

31.6

25.6

21.6

37.2

32.7

29.2

26.3

24.0

22.1

20.4

19.0

17.7

16.6

tmax (min.)

31.8

27.1

23.6

20.9

18.7

tmax (min.)

29.2

23.5

19.7

16.9

14.8

• True 2 W/kg WB SAR can be considered stress-free for most historical MRI exam durations

• MR manufacturers apply a margin to reported WB SAR – so that longer durations are also safe

• SAR comes with a ‘scan/exposure profile’

• A critical assumption is that users never expose vulnerable patients to high SAR

ΔTcore

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Peak Temperature evaluation Neufeld-Murbach model and real examination exposures

• Data extraction for 17010 exams at 1.5T from 100 randomly selected hospitals, scanned in April 2014

• Scans are effectively limited by Head SAR, Local Torso (LT), or Local Extremity (LE) SAR in the Philips implementation – LT: NM: 10 W/kg FL: 20 W/kg – LE: NM: 20 W/kg FL: 40 W/kg

• Use model parameters for hotspot temperature increase by Neufeld et al. (2015) DOI: 10.1002/bem.21919

• Note: starting temperature 36.7 ⁰C • CEM43 sensitivity to initial temperatures

evaluated for 38 ⁰C and 39 ⁰C

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Peak Temperature Evaluation – Example

Patient Id Scan Name Anatomy

lim SAR

Type

lim SAR

[W/kg]

Scan

Time

[sec]

Wait

Time

[sec]

tau

Regulated

Tinc

Regulated

T (after

scan)

Regulated

T (after

wait)

Regulated

CEM43

Regulated

tau

Impaired

Tinc

Impaired

T (after

scan)

Impaired

T (after

wait)

Impaired

CEM43

Impaired

tau

Basal

Tinc

Basal

T (after

scan)

Basal

T (after

wait)

Basal

CEM43

Basal

[patient_18103_1_]CoilSurveyScan KNEE LT 1.55 5 20 415.00232 0.6831082 36.6 36.6 4.674E-05 459.1524 0.939274 36.6 36.6 4.67E-05 641 0.372 36.6 36.6 4.67E-05

[patient_18103_1_]SURVEY_LEFT KNEE LE 2.06 15 45 393.78306 0.7875121 36.6 36.6 0.0001519 440.0714 1.082829 36.6 36.6 0.000152 641 0.4944 36.6 36.6 0.000152

[patient_18103_1_]SenseRefScan KNEE LE 0.13 8 23 553.67924 0.1978314 36.6 36.6 0.0002057 575.0435 0.272018 36.6 36.6 0.000206 641 0.0312 36.6 36.6 0.000206

[patient_18103_1_]PDW_aTSE KNEE LE 11.52 102 6 257.98766 1.862301 37.208167 37.202501 0.0006227 308.2146 2.560664 37.32147 37.31475 0.000664 641 2.7648 37.00673366 37.00294425 0.000553

[patient_18103_1_]STIR_longTE KNEE LE 15.56 127 5 235.19394 2.1643547 37.854169 37.844424 0.0018457 284.2769 2.975988 38.12946 38.11758 0.002305 641 3.7344 37.60172373 37.59394037 0.001419

[patient_18103_1_]COR_T1_1min_ KNEE LE 35.68 42 15 177.42653 3.2774499 38.272957 38.234263 0.002954 221.0199 4.506494 38.63485 38.58779 0.004065 641 8.5632 38.07399901 38.03990651 0.002238

[patient_18103_1_]T2W_FFE KNEE LE 0.23 78 3 529.85106 0.2631404 38.046572 38.039818 0.0045476 556.1519 0.361818 38.37501 38.36673 0.006621 641 0.0552 37.88125702 37.87527451 0.003481

[patient_18103_1_]PDW_SPAIR KNEE LE 19.75 107 19 217.73929 2.4384126 38.427511 38.374137 0.0075772 265.5634 3.352817 38.89273 38.82576 0.012005 641 4.74 38.40793565 38.35513273 0.006196

[patient_18103_1_]T2W_TSE_HR_SENSE KNEE LE 20.67 78 6 214.47828 2.4945596 38.59378 38.575205 0.0103126 262.0295 3.430019 39.13581 39.11218 0.017505 641 4.9608 38.72241452 38.70264062 0.009181

[patient_18103_1_]T2_TSE_VKB_2mm KNEE LE 13.88 40 7 243.76285 2.0441764 38.585643 38.564077 0.0120213 293.3414 2.810743 39.15024 39.12254 0.021182 641 3.3312 38.77696273 38.75331868 0.011327

[patient_18103_1_]STIR_longTE KNEE LE 15.57 127 6 235.14611 2.1650501 38.647944 38.628864 0.0170742 284.2261 2.976944 39.28628 39.26126 0.032846 641 3.7368 39.03792583 39.0152124 0.01898

[patient_18103_1_]PDW_SPAIR_HR KNEE LE 14.92 130 20 238.3295 2.1193762 38.666918 38.603423 0.0230672 287.603 2.914142 39.35322 39.26864 0.047879 641 3.5808 39.22917362 39.14840669 0.030785

[patient_18103_1_]T2W_TSE_korr_te KNEE LE 15.17 72 7 237.0869 2.1370586 38.638423 38.616284 0.0261143 286.2862 2.938456 39.32864 39.299 0.055689 641 3.6408 39.2644689 39.23553003 0.037686

[patient_18103_1_]COR_T1_1min_ KNEE LE 35.94 31 36 176.96108 3.2893696 38.820861 38.69957 0.0291724 220.4945 4.522883 39.53822 39.37775 0.063752 641 8.6256 39.51832796 39.35894563 0.045426

[patient_18103_1_]PDW_SPAIR_HR KNEE LE 14.92 90 1800 238.3295 2.1193762 38.705799 36.727019 0.0468408 287.603 2.914142 39.4144 36.76976 0.100361 641 3.5808 39.46660388 36.77290996 0.08365

Courtesy Manuel Murbach

SAR

Temperature

CEM43

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Temperature estimates (Neufeld – Murbach model) Final T from psSAR10g – all exams; Tb = 36.7 ⁰C

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

Problematic in terms of estimated local Temp. exceeding limit in 2-33

Temp. estimated for non-brain voxels

# patients

# patients with local temp less than 38.5 ⁰C

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

Cumulative Histogram

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CEM43 from psSAR10g (Neufeld – Murbach model) Tb = 36.7 ⁰C, all exams

0

2000

4000

6000

8000

10000

12000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

CEM43 (calculated)

LT Normal Perfl

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

HD Impaired Perf

Note the very low CEM43 under non-fever conditions (Tb = 36.7 ⁰C) Note that patients will still report unpleasant sensations (sweating)

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

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CEM43 from psSAR10g (Neufeld – Murbach model) Tb = 38 ⁰C, all exams

-2000

0

2000

4000

6000

8000

10000

12000

0 0.5 1 1.5 2 2.5

CEM43 (calculated)

LT Normal Perfl

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

HD Impaired Perf

If CEM43 = 2 min is ‘unconditionally’ safe, IEC First Level Mode is safe in most compromised patients, even with slight fever

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

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CEM43 from psSAR10g (Neufeld – Murbach model) Tb = 39 ⁰C, all scans

-2000

0

2000

4000

6000

8000

10000

12000

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

CEM43 (calculated)

LT Normal Perfl

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

HD Impaired Perf

In case of a real fever, RF exposure should better be limited to NM

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf0

2000

4000

6000

8000

10000

12000

37 37.5 38 38.5 39 39.5 40 40.5

Maximum Local Temperature (calculated)

LT Normal Perf

LT Impaired Perf

LE Normal Perf

LE Impaired Perf

HD Normal Perf

Head Impaired Perf

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CEM43 from psSAR10g – LT NM scans

1165

1170

1175

1180

1185

1190

1195

1200

1205

1210

1215

0 0.5 1 1.5 2 2.5 3 3.5 4

CEM43 (calculated)

LT Impaired Perf 36.7

LT Impaired Perf 38

LT Impaired Perf 39

Approx. 10% of NM (body) exams shows >2 CEM43 if patient presented with fever and under compromised conditions

Murbach model not validated for fever

1165

1170

1175

1180

1185

1190

1195

1200

1205

1210

1215

0 0.5 1 1.5 2 2.5 3 3.5 4

CEM43 (calculated)

LT Impaired Perf 36.7

LT Impaired Perf 38

LT Impaired Perf 39

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Discussion

• The low calculated temperatures and insignificant CEM43 corroborates the historical RF safety experience with MRI (100s millions patient examined)

• Calculated local temperatures from Murbach’s model exceed 40 ⁰C in a few cases – only for extremities of patient with compromised thermoregulation scanned in First Level controlled IEC mode – which is forbidden

– note: critical assumptions are low starting temperature – and constant Tcore

• Limiting exposure by local SAR effectively implies that WB SAR is well below 4 W/kg – Philips has no experience how psSAR10g > 20 or 40 W/kg affects RF safety

• The proposed level of CEM43 = 9 min cannot be justified based on Philips field data

• Existing RF safety control measures are generally sufficient • Awareness for Normal Mode should be improved • Philips invests in ALAP by providing more protocols tuned to NM exposure, and

provides a feedback to monitor the total deposited RF energy for comfort reasons

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