A. Martinez-Möller, M. Souvatzoglou, N. Navab, M. Schwaiger, S. Nekolla MR-based attenuation correction for whole-body MR/PET Journal of Nuclear Medicine 2008, 49 (suppl. 1), p65. Proceedings of Annual Meeting of Society of Nuclear Medicine (SNM 2008), New Orleans, LA, USA, June 2008 (bib)
	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.
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