The influence of ignoring higher bone attenuation on pelvic and spinal lesions in [18F]NaF PET/MRI examinations.


The influence of ignoring higher bone attenuation on pelvic and spinal lesions in [18F]NaF PET/MRI examinations.

Schramm, G.; Oehme, L.; Maus, J.; Hofheinz, F.; Petr, J.; Lougovski, A.; Beuthien-Baumann, B.; van den Hoff, J.

Aim: MRI-based attenuation correction (MRAC) in clinical whole-body PET/MRI imaging routinely is based on tissue type segmentation. Due to lack of MRI signal in cortical bone and the varying signal of spongeous bone, standard whole-body segmentation-based MRAC neglects the difference between the attenuation coefficient of soft tissue and the (higher) one of bone (MRAC-nobone). In the present work we have quantified the bias caused by MRAC-nobone in spinal and pelvic lesions in 20 PET/MRI examinations with [18F]NaF using the reconstructed PET standard uptake value (SUV) as the relevant measure. Methods: We reconstructed 20 PET/MRI [18F]NaF patient data sets acquired with a Philips Ingenuity TF PET/MRI. First, we used the vendor-provided MRAC-nobone algorithm to reconstruct PET-nobone. Second, we used a threshold-based algorithm developed in our group to automatically segment bone structures in the [18F]NaF PET images. Subsequently, an attenuation coefficient of 0.11 1/cm was assigned to the segmented bone regions in the MRI-based attenuation image (MRAC-bone) which was used to reconstruct PET-bone. The automatic bone segmentation algorithm was validated in 6 PET/CT [18F]NaF examinations. Finally, relative SUVmean and SUVmax differences between PET-bone and PET-nobone of 8 pelvic and 41 spinal lesions, and of other regions such as lung, liver, and bladder were calculated. Results: The comparison of [18F]NaF-based and CT-based bone segmentation in the 6 PET/CT patients showed a Dice similarity of 0.7 with a true positive fraction of 0.72 and a false positive fraction of 0.35. The [18F]NaF-based bone segmentation worked well in the pelvis and spine. However, it showed artifacts in the skull and in the extremities. The analysis of the 20 [18F]NaF PET/MRI examinations revealed relative SUVmax differences between PET-nobone and PET-bone of (-8.7% ? 2.7%, p = 0.01) and (-8.1% ? 1.9%, p = 2.4e-8) in pelvic and spinal lesions, respectively. A maximum SUVmax underestimation of -13.7% was found in lesion in the third cervical spine. The averaged SUVmean differences in volumes of interests in lung, liver and bladder were below 3%. Conclusion: Neglecting higher bone attenuation in MRAC leads to a systematic moderate SUV underestimation in spinal and pelvic lesions. The developed automatic [18F]NaF PET-based bone segmentation allows to include higher bone attenuation in whole-body MRAC and thus improves quantification accuracy for pelvic and spinal lesions in [18F]NaF PET/MRI examinations enabling direct comparisons to PET/CT examinations.

  • Lecture (Conference)
    Annual Congress of the European Association of Nuclear Medicine (EANM), 10.-14.10.2015, Hamburg, D
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 42(2015), S151
    DOI: 10.1007/s00259-015-3198-z

Permalink: https://www.hzdr.de/publications/Publ-22672
Publ.-Id: 22672