Attenuation correction in MR-BrainPET with segmented T1-weighted MR images of the patient's head - A comparative study with CT

Our method for attenuation correction (AC) in MR-BrainPET with segmented T1-weighted MR images of the pa-tient's head was applied to data from different MR-BrainPET scanners (Jülich, Tübingen) and compared to CT-based results. The study objectives presented in this paper are twofold. The first objective is to examine if the segmentation method developed for and successfully applied to 3D MP-RAGE data can also be used to segment other T1-weighted MR data such as 3D FLASH data. The second aim is to show if the similarity of segmented MR-based (SBA) and CT-based AC (CBA) obtained at HR+ PET can also be confirmed for BrainPET for which the new AC method is intended for. In order to reach the first objective, 14 segmented MR data sets (three 3D MP-RAGE data sets from Jülich and eleven 3D FLASH data sets from Tubingen) were compared to the resp. CT data based on the Dice coefficient and scatter plots. For bone, a CT threshold HU>;500 was applied. Dice coefficients (mean±std) for the upper cranial part of the skull, the skull above cavities, and in the caudal part including the cerebellum are 0.73±0.1, 0.79±0.04, and 0.49±0.02 for the Jülich data and 0.7U0.1, 0.72±0.1, and 0.60±0.05 for the Tubingen data. To reach the second aim, SBA and CBA were compared for six subjects based on VOI (AAL atlas) analysis. Mean absolute relative difference (maRD) values are m aRD (JUFVBWl-FDG): 0.99%±0.83%, m aRD (JüFVBW2-FDG): 0.90%±0.89%, and m aRD (JUEP-Fluma- zenil): 1.85%±1.25% for the Jülich data and m aRD (TuTP02- FDG): 2.99%±1.65%, m aRD (TuNP01-FDG): 5.37%±2.29%, and m aRD (TuNP02-FDG): 6.52%±1.69% for the three best-segmented Tübingen data sets. The results show similar segmentation quality for both Tl- weighted MR sequence types. The application to AC in BrainPET shows a high similarity to CT-based AC if the standardized ACF value for bone used in SBA is in good accordance to the bone density of the patient in question.