Validation of MR-Based Attenuation Correction of a Newly Released Whole-Body Simultaneous PET/MR System.

The aim of this study was to validate quantitative performance of a newly released simultaneous positron emission tomography (PET)/magnetic resonance imaging (MRI) scanner, by using MR-based attenuation correction (MRAC), both in phantom study and in patient study. PET/MRI image uniformities of a phantom under different hardware configurations were tested and compared. Thirty patients were examined with 2-deoxy-2-[F-18]fluoro-D-glucose (F-18-FDG) PET/computed tomography (CT) and subsequent PET/MRI. PET images from PET/MRI were corrected with MRAC (PETMR), CT-based attenuation maps (mu-maps, PETCT), and segmented CT mu-maps (PETCTSeg) derived from PET/CT. Standardized uptake values (SUVs) were compared among the 3 sets of PET in main organs (bone, liver and lung) and in 52 FDG-avid lesions, including soft-tissue lesions and bone lesions. The result showed that PET imaging uniformities of PET/MRI under different configurations were good (<8.8%). The SUV differences among the 3 sets of PET varied with organs and lesion types. In detail, the mean relative differences of SUV between PETMR and PETCT were as follows: -18.8%, bone (SUVmean); -8.0%, liver (SUVmean); -12.2%, lung (SUVmean); -18.1%, bone lesions (SUVmean); -13.3%, bone lesions (SUVmax); -8.2%, soft-tissue lesions (SUVmean); and -7.3%, soft-tissue lesions (SUVmax). The mean relative differences between PETMR and PETCTSeg were as follows: -19.0%, bone (SUVmean); -3.5%, liver (SUVmean); -3.3%, lung (SUVmean); -19.3%, bone lesions (SUVmean); -17.5%, bone lesions (SUVmax); -5.5%, soft-tissue lesions (SUVmean); and -4.4%, soft-tissue lesions (SUVmax). The differences of SUV between PETMR and PETCT were larger than those between PETMR and PETCTSeg, in both soft tissue and soft-tissue lesions (P<0.001), but not in bone or bone lesions. In conclusion, MRAC in the newly released PET/MR system is accurate in most tissues, with SUV deviations being generally less than 10%, compared to PET/CT. In bone, however, underestimations can be substantial, which may be partially attributed to segmentation of the MR-based mu-maps.