Intra-individual qualitative and quantitative comparison of [⁶⁸Ga]Ga-DOTATATE PET/CT and PET/MRI

Background: Somatostatin receptor (SSTR) positron emission tomography (PET) is a cornerstone of neuroendocrine tumor (NET) management. Hybrid PET/magnetic resonance imaging (MRI) is now available for NET-imaging, next to PET/computed tomography (CT).Objectives: To determine whether CT or MRI is the best hybrid partner for [Ga-68]Ga-DOTATATE PET.Design: Monocentric, prospective study.Methods: Patients received a same-day [Ga-68]Ga-DOTATATE PET/CT and subsequent PET/MRI, for suspicion of NET, (re)staging or peptide receptor radionuclide therapy-selection. The union (PETunion) of malignant lesions detected on PETCT and PETMRI was the reference standard. Concordance of detection of malignant lesions in an organ was measured between PETunion and CT and PETunion and MRI. Seven bins were used to categorize the number of malignant lesions, containing following ordinal variables: 0, 1, 2-5, 6-10, 11-20, >20 countable and diffuse/uncountable. The difference in number of malignant lesions was obtained as the difference in bin level ('Delta bin') between PETunion and CT and PETunion and MRI with a Delta bin closer to zero implying a higher concordance rate.Results: Twenty-nine patients were included. Primary tumors included 17 gastroenteropancreatic-NETs, 1 colon neuroendocrine carcinoma, 7 lung-NETs and 2 meningiomas. Patient level concordance with PETunion was 96% for MRI and 67% for CT (p = 0.039). Organ level concordance with PETunion was 74% for MRI and 40% for CT (p < 0.0001). In bone, there was a higher concordance rate for MRI compared to CT, 92% and 33%, respectively (p = 0.016). Overall, a mean Delta bin of 0.5 +/- 1.1 for PETunion/MRI and 1.4 +/- 1.2 for PETunion/CT (p < 0.0001) was noted. In liver, a mean Delta bin of 0.0 +/- 1.1 for PETunion/MRI and 1.7 +/- 1.2 for PETunion/CT was observed (p = 0.0078). In bone, a mean Delta bin closer to zero was observed for PETunion/MRI compared to PETunion/CT, 0.6 +/- 1.4 and 2.0 +/- 1.5, respectively (p = 0.0098).Conclusions: Compared to SSTR PET/CT, SSTR PET/MRI had a higher patient and organ level concordance for malignant tumoral involvement and number of malignant lesions, with a clear added value in bone and liver specifically.