Recently, an exhaustive examination of 11 state of the art MR-based attenuation correction (AC) concluded that there are currently a few methods showing similar results compared to the gold-standard, CT-based AC. While the study presented a thorough portfolio of metrics to quantify accuracy (bias) and quality, it lacked one of the most important metrics to quantify robustness that is critical for its clinical applicability: intrascanner reproducibility (repeatability). In this work, we provide for the first time a study of the repeatability of one of the outperforming brain MR-based AC methods: the SPM-based pseudo-CT approach. 22 subjects undergoing 3 18F-FDG PET/MRI visits within 2 months were retrospectively analyzed in this study. Pseudo-CT mu-maps were obtained from the coregistered MR images for all 3 visits and the PET data from visit 1 was reconstructed using all three mu-maps. Relative changes (RC), Intraclass correlation coefficient (ICC), Reproducibility coefficient (RDC95%) and Bland-Altman Limits of Agreement (LoA) were used to measure repeatability. Voxel-based and ROI-based results showed that absolute RC for the reconstructed PET images are within ~2%. The brain cortex and the cerebellum were the regions with the largest variability (~3%). The differences across visits were not statistically significant (p=0.90). In conclusion this study shows for the first time the repeatability of the SPM-based pseudo-CT approach for brain MR-AC. These results, in addition to the ease of implementation and the quality and robustness previously demonstrated, confer this SPM-based method an ideal candidate for routine brain PET/MRI research and clinical studies.
Keywords: MRI; PET; PET/MRI; attenuation correction; pseudo-CT; repeatability.