642 Objectives Respiratory motion leads to blurred structures in PET images of the abdomen and thorax, and hence hampers the detection and quantification of lesions. An MR-based motion-correction framework for PET images was evaluated quantitatively. Methods On an integrated PET/MR (Siemens Biograph mMR) 5 minutes of PET as well as radial MR data (T1-weighted, stack-of-stars 3D, spoiled GRE, golden-angle sampling, Resolution: 1.56x1.56x4.5mm3) were acquired simultaneously. A respiratory signal was extracted from the k-space of the MR data (“self-gating”) and used to sort MR acquisitions and PET listmode events into 5 respiratory bins (1). A high-resolution motion model was calculated from the reconstructed MR-bins using non-rigid registration. The PET images were reconstructed by means of a prototypical motion-correction software (Siemens Molecular Imaging, Knoxville), which uses gated sinograms and the motion model to iteratively calculate a motion-compensated PET image (2). The lesions were analyzed conventionally with regard to their shape (rising and falling lesion edge) as well as their tracer activity concentration. In addition, image sharpness was evaluated using a frequency-threshold metric, which detects the occurrence of high spatial frequencies and resembles a more realistic assessment of improved object appearance. Results F-18 FDG (n = 8) and Ga-68 DOTANOC (n = 7) PET/MR data of 15 patients (55 ± 18 y) were reconstructed by means of the motion-correction framework as well as using conventional averaging. The motion compensation increased the image sharpness by 49.8%. In 19 evaluated lesions motion compensation led to a median increase in SUVpeak by 10.4±7.6% (mean ± SD). The slope of the cranio-caudal lesion edges increased by 34.9±53.3% and 39.5±42.1%. The attached figure depicts sagittal slices of uncompensated and motion-compensated reconstructions, as well as cranio-caudal intensity profiles through the depicted lesion. Conclusions MR-based motion correction in PET images using all available data leads to significantly sharper PET structures without compromising SNR.

256 Objectives To compare diagnostic performance between PET/CT and recently introduced intergrated whole-body PET/MR concerning evaluation of brain tumours. Methods Twenty pts, referred to [18F]FET-PET for evaluation of brain tumors, underwent a single-injection/dual-imaging protocol, including a PET/CT scan (Siemens Truepoint 64, 32±5 min p.i., 10 min 3D acquisition) and a subsequent MR/PET scan (Siemens mMR, 52±8 min p.i., 15 min 3D acquisition), after injection of 183±44 MBq [18F]FET. Images were reconstructed with filtered backprojection (Hann 4.9mm, zoom 2.5), attenuation correction was performed using low dose CT for the PET/CT and Dixon-MR sequences for the PET/MR. Images were interpreted visually and by semiquantitative analysis. The respective lesion and Bg SUVs were compared as well as the lesion/background ratios (T/Bg) using the wilcoxon test. Results Visual interpretation turned out suspicion of tumour tissue in 16/20 scans with both PET/MR and PET/CT, 4/20 patients were read as negative. Overall, SUVmax, SUVmean of the lesion and SUVmean of the Bg. calculated in the respective scans were significantly different: Average lesion SUVmax PET/CT: 3.1±1.2, average lesion SUVmax PET/MR: 2.7±1.0; av. lesion SUVmean PET/CT: 2.7±1.1, av. lesion SUVmean PET/MR: 2.2±0.8; av. Bg SUVmean PET/CT: 1.2±0.2, av. Bg SUVmean PET/MR: 1.0±0.2 (p Conclusions Imaging of brain tumors with [18F]FET is feasible with the integrated whole-body PET/MR-scanner with high image quality. Despite technological differences, the semiquantitative evaluation of [18F]FET-PET data with PET/MR concerning T/Bg. ratios reveals comparable results as with PET/CT, indicating that established lesion/background ratio thresholds for distinguishing malignant brain tumor tissue, can be transferred

Purpose Neuroendocrine tumours are frequently located in the upper abdomen and especially in the pancreas. Imaging of the abdomen with somatostatin analogs such as 68 Ga-DOTA-Phe 1 -Tyr 3 -octreotide (DOTATOC) is a standard approach for imaging neuroendocrine cancer, but is still challenging due to physiological and technical considerations in this area. Therefore, the aim of this study was to further investigate the origin of 68 Ga-DOTATOC findings in the pancreas. Methods Forty-three consecutive patients with neuroendocrine tumours were examined by 68 Ga-DOTATOC positron emission tomography (PET)/CT for staging or restaging. As imaging of the upper abdomen is frequently affected by breathing artefacts, PET and CT data were analysed for misalignment and rearranged if necessary. Any noticeable uptake in the pancreas was described. Tracer uptake in the head of the pancreas and the liver was measured by means of maximum and average standard uptake value (SUV max , SUV av ). The reference standards (malignant versus benign) for correlation with PET findings were clinical and radiological follow-up (mean follow-up time 14 months) ( n = 37) or histological confirmation ( n = 6). Results In 23 of 43 studies (54%) misalignment between PET and CT data was found with a mean value of 1.4 cm. Visual assessment demonstrated that 20 of 43 scans (46.6%) showed no uptake in the head of the pancreas. Of 43 scans, 23 (53.4%) showed noticeable uptake with focal pattern in the head of the pancreas in 10 scans and irregular pattern in 13 scans. Follow-up indicated malignant pancreatic lesions in three patients. The pancreatic head to liver SUV av ratios in these patients ranged from 1.62 to 6.85, whereas in cases of uptake without known malignancy ratios ranged from 0.56 to 1.19. Considering SUV max , the ratio ranged from 3.24 to 9.1 and from 0.84 to 1.47, respectively. No statistically significant difference was noted between uptake in the head of the pancreas and the liver in patients without malignant pancreatic tumours ( p > 0.05). Conclusion 68 Ga-DOTATOC uptake in the head of the pancreas is a common finding in patients undergoing 68 Ga-DOTATOC PET/CT. However, this finding most likely represents a physiological condition, especially if the uptake in the pancreatic head is similar to the uptake in the liver (uptake ratio head to liver SUV av < 1.4). Therefore, quantification is recommended to avoid false-positive diagnosis. Misalignment due to respiratory motion must always be taken into account.

During [90Y]DOTATOC therapy, for determination of kidney doses a conventional approach using co-injected [111In]DOTATOC was evaluated for validity, reliability and reproducibility as well as for the influence of methodological variations and bremsstrahlung. Biologically effective doses were estimated by calculating the relative effectiveness (RE) of kidney doses.