Intra-Individual Comparison of (124)I-PET/CT and (124)I-PET/MR Hybrid Imaging of Patients with Resected Differentiated Thyroid Carcinoma: Aspects of Attenuation Correction

SIMPLE SUMMARY: This study evaluates the qualitative and quantitative differences between 124-iodine PET/CT and PET/MR in oncologic patients with differentiated thyroid carcinoma after thyroidectomy. The impact of improved MR-based attenuation correction (AC) using a bone atlas was analysed in PET/MR data. Despite different patient positioning and AC methods PET/CT and PET/MR provide overall comparable results in a clinical setting. The overall number of detected (124)I-active lesions and the measured average SUV(mean) values for congruent lesions were higher for PET/MR when compared to PET/CT. The addition of bone to the MR-based AC in PET/MR slightly increased the SUV(mean) values for all detected lesions. ABSTRACT: Background: This study evaluates the quantitative differences between 124-iodine (I) positron emission tomography/computed tomography (PET/CT) and PET/magnetic resonance imaging (PET/MR) in patients with resected differentiated thyroid carcinoma (DTC). Methods: N = 43 (124)I PET/CT and PET/MR exams were included. CT-based attenuation correction (AC) in PET/CT and MR-based AC in PET/MR with bone atlas were compared concerning bone AC in the head-neck region. AC-map artifacts (e.g., dentures) were noted. Standardized uptake values (SUV) were measured in lesions in each PET data reconstruction. Relative differences in SUV(mean) were calculated between PET/CT and PET/MR with bone atlas. Results: Overall, n = 111 (124)I-avid lesions were detected in all PET/CT, while n = 132 lesions were detected in PET/MR. The median in SUV(mean) for n = 98 congruent lesions measured in PET/CT was 12.3. In PET/MR, the median in SUV(mean) was 16.6 with bone in MR-based AC. Conclusions: (124)I-PET/CT and (124)I-PET/MR hybrid imaging of patients with DTC after thyroidectomy provides overall comparable quantitative results in a clinical setting despite different patient positioning and AC methods. The overall number of detected (124)I-avid lesions was higher for PET/MR compared to PET/CT. The measured average SUV(mean) values for congruent lesions were higher for PET/MR.