Objectives: To perform scatter and attenuation correction in future whole-body MR/PET devices, it is necessary to determine an attenuation map with the attenuating factors for 511 keV photons. We investigated an attenuation map derived from proton-weighted MR data through segmentation into 4 classes: background, lungs, fat and soft tissue. The accuracy of the attenuation and scatter correction in cancer patients using this map as compared to CT-based attenuation maps was evaluated. Methods: 35 oncology patients were examined with FDG in a Biograph16 PET/CT. Regions of interest were manually defined in 52 FDG-avid lesions located in the lungs (15), bones (21) and neck (16). The PET datasets were retrospectively reconstructed using the attenuation map segmented in 4 classes and the changes in SUV were quantified. In patients who underwent both a PET/CT and a proton-weighted MR, the CT and MR datasets were non-rigidly registered and the PET data reconstructed using the CT-based and MR-based attenuation maps. SUVs of 6 manually defined ROIs were compared in the 2 PET reconstructions. Results: The SUV difference between the PET images reconstructed with the original and the segmented attenuation map was 1.7±0.7%, 7.3±2.8%, 2.9±1.7% for the lung, bone and neck lesions respectively. The largest SUV difference observed was 13% for a hip lesion. For patients who underwent both PET/CT and MRI examinations, the average SUV difference was 5.5%. Conclusions: No clinically relevant differences were observed when using a segmented attenuation map without bone delineation as compared to the original CT-based maps. However, a moderate SUV decrease for bone lesions was observed.     «

Objectives: To perform scatter and attenuation correction in future whole-body MR/PET devices, it is necessary to determine an attenuation map with the attenuating factors for 511 keV photons. We investigated an attenuation map derived from proton-weighted MR data through segmentation into 4 classes: background, lungs, fat and soft tissue. The accuracy of the attenuation and scatter correction in cancer patients using this map as compared to CT-based attenuation maps was evaluated. Methods: 3...     »