Quantitative accuracy of MR-based attenuation correction in whole-body PET/MR

Transcription

1 Georg Schramm I Institute Prof. Radiopharmacy Peter Mustermann PET I Center Institut I xxxxx g.schramm@hzdr.de I Quantitative accuracy of MR-based attenuation correction in whole-body PET/MR G. Schramm 1, J. Langner 1, F. Hofheinz 1, B. Beuthien-Baumann 2, I. Platzek 2, J. Petr 1, J. Kotzerke 2, J. Steinbach 1, J. van den Hoff 1 1 Helmholtz-Zentrum Dresden-Rossendorf 2 Universitätsklinikum Carl Gustav Carus, Dresden

2 Introduction PET/MR in Dresden: since Jan 2011 Philips Ingenuity TF PET/MR in operation at HZDR until now more than 650 examinations (mostly whole-body) additionally stand-alone Siemens HR + PET Attenuation correction (AC) for PET: essential to obtain quantitave values mean free path of 511 kev Photons in water 10 cm conventionally performed with transmission scan or scaling of Hounsfield units 2

3 MR-based attenuation correction (MRAC) in PET/MR no transmission or CT scan available in PET/MR MR signal not related to photon attenuation software-based AC used in PET/MR segmentation and classification of 3 tissue types (air, lung, soft tissue) of an MR image assignment of respective attenuation coefficients (0, 0.22, 0.96 cm -1 ) atmr image MR-based att. map (MRMap) MR-based attenuation correction (MRAC) air, soft tissue + lung segmentation of MR image assigment of respective attenuation coefficients 3

4 Objective previous works central question How accurate is segmented MRAC? our investigations several groups already compared segmented MRAC vs CT-based AC 1 deviations of ca. 5-15% found depending on ROI location CT image has to be scaled for AC 1 e.g.: Keereman et al., Med. Phys. 38, 2011 Martinez-Möller et al., JNM 50, 2009 Schulz et al., EJNMMI 38, 2011 Hofmann et al., JNM 36 S1, 2009 direct comparison of vendor-provided MRAC vs transmission-based AC (TRAC) analysis of 13 patient data sets examined in HR + and voluntarily in PET/MR on the same day twofold reconstruction of PET/MR emission data (1) vendor-provided MRAC (2) alinged TRAC from HR + comparison of resulting PET images in different ROIs 4

5 Materials & Methods (1) 5

6 Materials & Methods (1) 5

7 Results I visual comparison of attenuation maps correct lung, soft tissue segmentation in 11 cases 2 cases with errorneous lung sementation low signal MR signal below lung errorneous lung expansion in caudal direction strong heart motion artifacts complete failure of lung detection adaption of segmentation lung threshold correct lung segmentation 6

8 Results ll SUV correlation in the body stem mean +- sd median range

9 Results lll SUV correlation in the lung mean +- sd median range case with errorneous lung segmentation 8

10 Results lll SUV deviations in various ROIs ROI in liver ROI in cerebellum various hot focal structures median range median range median range -5% (-18 8)% 12% (6 9)% -6% (-17 22)% e.g.: brown fat lung tumors lymphomas thoracic spine 9

11 Discussion Outlook improve atmr sequence + segmentation to reduce misclassification adjust attenuation coefficient for lung remove truncation artifacts include attenuation of all used coils Thanks to all members of PET Center Dresden-Rossendorf & Z.Hu, S. Prevrhal, S. Reinisch, T. Guo 10

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13 Segmentation errors due to metal implants MR orig. MRMap corr. MRMap orig. PET corr. PET orig/corr PET

14 Truncation artifacts BMI = 20 orig. MRMap corr. MRMap orig. PET corr. PET orig/corr PET

15 Truncation artifacts BMI = 25 orig. MRMap corr. MRMap orig. PET corr. PET orig/corr PET

16 Truncation artifacts BMI = 43 orig. MRMap corr. MRMap orig. PET corr. PET orig/corr PET