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

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 124I 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 SUVmean were calculated between PET/CT and PET/MR with bone atlas. Results: Overall, n = 111 124I-avid lesions were detected in all PET/CT, while n = 132 lesions were detected in PET/MR. The median in SUVmean for n = 98 congruent lesions measured in PET/CT was 12.3. In PET/MR, the median in SUVmean was 16.6 with bone in MR-based AC. Conclusions: 124I-PET/CT and 124I-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 124I-avid lesions was higher for PET/MR compared to PET/CT. The measured average SUVmean values for congruent lesions were higher for PET/MR.

Systematic evaluation of human soft tissue attenuation correction in whole‐body PET/MR: Implications from PET/CT for optimization of MR‐based AC in patients with normal lung tissue

“…Due to breathing motion, the ribs are difficult to be considered in the bone atlas, and adding bone information to the arms might be challenging due to the different patient position in both hybrid modalities (PET/CT and PET/MR) and due to truncation artifacts at off‐center positions. Thus, an adapted bone atlas including ribs and arm bones might even result in more registration errors, which is already known as a limitation of the atlas‐based AC approaches 44,45 . The impact of bone in the AC is locally very limited as shown in the VOI analysis (Table 3), where inter‐costal or cervical‐clavicular VOIs show less than −1% deviation to the CT‐AC reference.…”

“…Thus, an adapted bone atlas including ribs and arm bones might even result in more registration errors, which is already known as a limitation of the atlas-based AC approaches. 44,45 The impact of bone in the AC is locally very limited as shown in the VOI analysis (Table 3), where inter-costal or cervical-clavicular VOIs show less than −1% deviation to the CT-AC reference. For the assessment of bone lesions an improved and further individualized bone atlas could be beneficial, but the overall impact on PET data is very small due to the neglectable volume proportion of missing bones and the limited only local impact.…”