Evaluation of an atlas-based PET head attenuation correction using PET/CT & MR patient data

The goal of this study was to compare MR-based PET patient attenuation correction (AC) to CT-based AC in the head using clinical whole-body FDG-PET patient data obtained from a tri-modality PET/CT & MR setup. The MR-based AC utilizes an atlas-based approach, registering the patient's MR images to a CT-based atlas, producing 'pseudoCT' images. Thirteen clinical whole-body FDG patients were included in this study. PET mean activity concentration values were measured and compared in six ~15ml volumes-of-interest throughout the brain tissue. The AC methods compared to CT-based AC were segmentation of the CT (air, fat, soft tissue) and atlas-based MRAC. Results: PET activity concentration was systematically under-estimated on average by 1.32 kBq/ml (4.9%) when using the segmented CT-based AC, mainly due to lack of attenuation correction for skull bone. Using the atlas-based method, the error was reduced to 0.03 kBq/ml (0.2%) on average. Examination of the resulting PET images shows the spatial variation induced by these methods based upon the approximations made. Conclusion: The results demonstrate that the atlas-based AC in the head provides adequate PET quantitation and image quality as compared to methods which did not include bone.