Comparison of ⁶⁸Ga-DOTATOC PET acquired by an integrated hybrid PET/MR and a PET/CT scanner in patients with neuroendocrine tumors

Objectives Evaluation of diagnostic PET image quality of ⁶⁸Ga-DOTATOC performed on a PET/MR and a PET/CT scanner in patients with neuroendocrine tumors.

Methods 30 patients underwent sequential PET/CT (Siemens Biograph Truepoint 64, mean 17±3 min p.i., 22/30 underwent diagnostic CT) and PET/MR (Siemens mMR, mean 82±16 min p.i., 17/30 underwent diagnostic MR) after a single injection of ⁶⁸Ga-DOTATOC (mean 123±15 MBq). Images were reconstructed using OSEM3D (3 iterations, 21 subsets). Conspicuity of lesions was evaluated by consensus reading of two nuclear medicine physicians (visual scoring from 0 to 3). SUV was measured in normal organs and pathologic lesions.

Results 159 lesions were scored visually in 21/30 patients. Scores were slightly higher on PET/CT (average score 2.67 vs 2.58), however there was no significant difference regarding lesion detectability. On PET/MR some artifacts related to scatter correction occurred around areas with high activity, which is currently being optimized. SUV comparison between PET/MR and PET/CT was possible in 19 patients. SUV of pathologic lesions (48 lesions were evaluated for SUV) did not differ significantly between PET/MR and PET/CT (mean ratio SUV_MR/SUV_CT=1.06±0.28, R²=0.79). Regarding normal organs, the mean ratio SUV_MR/SUV_CT for pituitary, liver, spleen, mediastinum, muscle and lung was 1.33±0.55, 0.95±0.11, 1.02±0.11, 0.54±0.16, 0.80±0.12 and 0.50±0.22, respectively (R²=0.98). Diagnostic MR could be acquired in good technical quality in parallel to PET.

Conclusions Diagnostic quality of ⁶⁸Ga-DOTATOC PET sequentially acquired on a PET/CT and a PET/MR scanner was comparable; there was no significant difference in lesion SUV. Subjective PET image quality and visual lesion scoring was slightly higher on the PET/CT, most probably related to better count statistics. Future prospective studies in a larger patient collective are now warranted to evaluate the potential clinical benefit of diagnostic PET/MR to diagnostic PET/CT.

Research Support Siemens Research Cooperation MR/PE