Test–Retest Repeatability of [ 18 F]FDG Uptake by Solid Tumors on PET/MRI: A Prospective, Multicenter Study Using the QIBA Protocol

Prior oncologic PET/MRI repeatability studies have been limited by single-center designs, small cohorts, or select patient populations. Our primary aim was to estimate the test–retest repeatability of uptake metrics on [18F]FDG PET/MRI studies across a variety of cancer types. A secondary aim was to assess the impact of intersession μ-map variability on repeatability. Methods: In this prospective study involving 2 institutions with different PET/MRI scanners, subjects completing standard-of-care [18F]FDG PET/CT or MRI examinations were recruited to undergo 2 research [18F]FDG PET/MRIs (i.e., test and retest) within a 1–9 d period per Quantitative Imaging Biomarker Alliance specifications. Enrollment required at least 1 measurable lesion (long axis ≥ 2 cm, known or expected SUVmax ≥ 4.0) and no active oncologic therapy. SUVmax and SUVpeak were extracted from measurable lesions (1–5 per subject). At site 1, attenuation-coefficient maps (i.e., μ-maps) were inspected for substantial differences across sessions. Additionally, at site 1, the retest μ-map was coregistered to the test μ-map, and the PET attenuation-correction process was repeated for the test session based on the retest μ-map. Intersession repeatability was assessed via Bland–Altman plots, and within-subject coefficients of variation (wCVs) were calculated. Results: At site 1, 10 subjects with 11 measurable lesions were analyzed, and the wCVs for SUVmax and SUVpeak were 12.3% and 9.6%, respectively. At site 2, 11 subjects with 30 measurable lesions were analyzed, and the wCVs for SUVmax and SUVpeak were 9.5% and 8.8%, respectively. At site 1, repeating attenuation correction of the test PET data with the retest μ-map slightly improved repeatability, reducing the wCV to 10.1% for SUVmax and to 9.1% for SUVpeak. For 8 of 11 lesions at site 1, the μ-map substitution altered the test–retest change by less than 5%, with no appreciable intersession μ-map differences or artifacts. Conclusion: The test–retest repeatability of SUVmax among hypermetabolic lesions on [18F]FDG PET/MRI, using data from 2 scanner models, was similar to the Quantitative Imaging Biomarker Alliance’s wCV benchmark of 10%–12% for [18F]FDG PET/CT. Intersession μ-map variations had minimal negative impact on repeatability.