Objectives: The primary aims of this study were to evaluate the feasibility of simultaneous 68(DOTA(0)-Phe(1)-Tyr(3))octreotide positron emission tomography (PET)/magnetic resonance (MR) acquisition on a fully integrated PET/MR scanner in patients and to compare the quality of PET images acquired with a PET/MR device with those acquired with a PET/computed tomography (CT) scanner.
Patients and methods: Sequential PET/CT and PET/MR imaging was performed in 24 patients with neuroendocrine tumors using a single-injection/dual-imaging protocol. After intravenous injection of 68Ga-DOTATOC (mean, 120 MBq), PET/CT imaging including low-dose CT was performed at a mean time of 17 minutes post injection, and subsequently, PET/MR imaging including a Dixon sequence for attenuation correction was started at a mean time of 82 minutes post injection. The PET/CT and PET/MR images were analyzed visually using a 4-point scale for quality, coregistration, anatomical correlation, and lesion conspicuity. The standardized uptake value of background organs and focal lesions was measured and compared between the PET/CT and PET/MR acquisitions.
Results: 68Ga-DOTATOC PET acquired on the PET/MR delivered images with a good diagnostic quality (average visual rating PET/CT, 2.83; PET/MR, 2.08; P <; 0.01). The standardized uptake value of focal lesions did not differ between the PET/CT and PET/MR acquisitions (P >; 0.3) and correlated in a linear fashion (correlation coefficient ρ = 0.90). Lesion conspicuity was slightly, but significantly, higher on the PET/CT acquisitions (PET/CT, 2.71; PET/MR, 2.62; P = 0.01). Positron emission tomography/MR detected 153 of 157 lesions identified by PET/CT; however, there was no difference in sensitivity on a patient basis or organ system basis. Anatomical correlates for focal PET lesions could significantly more often be delineated using MR Dixon images compared with low-dose CT (average visual rating PET/CT, 1.78; PET/MR, 2.30; P <; 0.01). Coregistration of functional and morphological data was better on PET/MR compared with PET/CT, which, however, did not reach significance (average visual rating PET/CT, 2.17; PET/MR, 2.46; P = 0.10).
Conclusions: 68Ga-DOTATOC PET/MR imaging is feasible in patients, with good image quality, and detectability of focal PET lesions was equivalent to PET/CT on a patient basis and organ system basis. Now, the clinical value of 68Ga-DOTATOC PET/MR with additional diagnostic MR protocols has to be evaluated against PET/CT with multiphase contrast-enhanced CT protocols in future studies.