A. Drzezga, M. Souvatzoglou, M. Eiber, A. Beer, S. Fürst, A. Martinez-Möller, S. Nekolla, S. I. Ziegler, C. Ganter, E. Rummeny, M. Schwaiger First clinical experience of integrated whole-body PET/MR. Comparison to PET/CT in patients with oncological diagnoses. Journal of Nuclear Medicine 2012;53(6):845-855. (bib)
	The recently introduced first integrated whole-body PET/MR scanner (Siemens Healthcare Biograph mMR) allows simultaneous acquisition of PET and MR data in humans and, thus, may offer new opportunities, particularly regarding diagnostics in oncology. This scanner features major technological differences compared to conventional PET/CT devices, including the replacement of photomultipliers with avalanche photodiodes and the need for MR-based attenuation correction. Aim of this study was to evaluate comparability of the clinical performance between conventional PET/CT and PET/MR in patients with oncological diseases. Methods: Thirty-two patients with different oncological diagnoses underwent a single-injection/ dual-imaging protocol, consisting of a PET/CT and subsequent PET/MR scan. PET/CT scans were performed according to standard clinical protocols (85±9 min p.i. of 400±44MBq [18F]FDG, 2 min/bed position (BP)). Subsequently (140±24min p.i.), PET/MR was performed (4 min/BP). PET-images of both modalities were reconstructed iteratively (AW OSEM 3D), attenuation and scatter correction and regional allocation was performed using low dose CT data for PET/CT and Dixon-MR sequences for PET/MR. PET/MR and PET/CT were compared visually by two teams of observers by rating the number and location of suspicious lesions as well as image quality and alignment. For quantitative comparison, SUV-based assessment of the detected lesions and different tissue types was carried out. Results: Simultaneous PET/MR acquisition was feasible with high quality in short acquisition times (=20 min). No significant difference was found between the numbers of suspicious lesions (n=80) or lesion-positive patients (n=20) detected with PET/MR or PET/CT. Anatomical allocation of PET/MR findings by means of the Dixon-MR sequence was comparable to allocation of PET/CT-findings by means of the low-dose CT. Quantitative evaluation revealed a high correlation (?=0.93) between mean SUV measured in lesions with PET/MR or PET/CT, respectively. Conclusion: This study demonstrates for the first time that integrated whole-body PET/MR imaging is feasible in a clinical setting with high quality and in a short examination time. PET/MR allowed the detection of tumor-suspect hypermetabolic lesions in patients with oncological diagnoses with comparable reliability as with PET/CT. Despite different attenuation correction approaches, the tracer-uptake in suspicious lesions correlated well between PET/MR and PET/CT. The Dixon MR sequences acquired for attenuation correction also may serve for anatomical allocation of PET findings obtained by PET/MR in the entire body. These encouraging results may form the foundation for future studies, aiming to define the added value of PET/MR over PET/CT.
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