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Correction of quantification errors in pelvic and spinal lesions caused by ignoring higher photon attenuation of bone in [ 18 F]NaF PET/MR
Author(s) -
Schramm Georg,
Maus Jens,
Hofheinz Frank,
Petr Jan,
Lougovski Alexandr,
BeuthienBaumann Bettina,
Oehme Liane,
Platzek Ivan,
Hoff Jörg
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4932367
Subject(s) - correction for attenuation , nuclear medicine , attenuation , magnetic resonance imaging , positron emission tomography , segmentation , standardized uptake value , medicine , cortical bone , attenuation coefficient , radiology , physics , computer science , pathology , artificial intelligence , optics , quantum mechanics
Purpose: MR‐based attenuation correction (MRAC) in routine clinical whole‐body positron emission tomography and magnetic resonance imaging (PET/MRI) is based on tissue type segmentation. Due to lack of MR signal in cortical bone and the varying signal of spongeous bone, standard whole‐body segmentation‐based MRAC ignores the higher attenuation of bone compared to the one of soft tissue (MRAC nobone ). The authors aim to quantify and reduce the bias introduced by MRAC nobone in the standard uptake value (SUV) of spinal and pelvic lesions in 20 PET/MRI examinations with [ 18 F]NaF. Methods: The authors reconstructed 20 PET/MR [ 18 F]NaF patient data sets acquired with a Philips Ingenuity TF PET/MRI. The PET raw data were reconstructed with two different attenuation images. First, the authors used the vendor‐provided MRAC algorithm that ignores the higher attenuation of bone to reconstruct PET nobone . Second, the authors used a threshold‐based algorithm developed in their group to automatically segment bone structures in the [ 18 F]NaF PET images. Subsequently, an attenuation coefficient of 0.11 cm −1 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 six PET/CT [ 18 F]NaF examinations. Relative SUV mean and SUV max 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. By varying the assigned bone attenuation coefficient from 0.11 to 0.13 cm −1 , the authors investigated its influence on the reconstructed SUVs of the lesions. Results: The comparison of [ 18 F]NaF‐based and CT‐based bone segmentation in the six PET/CT patients showed a Dice similarity of 0.7 with a true positive rate of 0.72 and a false discovery rate of 0.33. The [ 18 F]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 [ 18 F]NaF PET/MRI examinations revealed relative SUV max differences between PET nobone and PET bone of (−8.8% ± 2.7%, p = 0.01) and (−8.1% ± 1.9%, p = 2.4 × 10 −8 ) in pelvic and spinal lesions, respectively. A maximum SUV max underestimation of −13.7% was found in lesion in the third cervical spine. The averaged SUV mean differences in volumes of interests in lung, liver, and bladder were below 3%. The average SUV max differences in pelvic and spinal lesions increased from −9% to −18% and −8% to −17%, respectively, when increasing the assigned bone attenuation coefficient from 0.11 to 0.13 cm −1 . Conclusions: The developed automatic [ 18 F]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 [ 18 F]NaF PET/MRI examinations. In nonbone structures (e.g., lung, liver, and bladder), MRAC nobone yields clinically acceptable accuracy.