Abstract
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Objectives Imaging with F-18-Sodium Fluoride (NaF) PET/CT, a bone metabolism tracer, has shown success in detection of bone tumors. For quantitative applications, repeatability is degraded due to various factors. The objective of this study was to assess the impact of image acquisition factors and patient characteristics on the repeatability of NaF PET/CT-derived SUV measures in individual bone lesions using linear mixed effects analysis.
Methods Thirty-four patients with metastatic castrate-resistant prostate cancer received two NaF PET/CT pre-treatment scans (within 3±2 days of each other) in a multi-center therapeutic study. Regions of interest (ROI) were segmented with an SUV threshold of 15 and a minimum volume of 1.5 cubic cm. For each ROI, uptake was quantified with the maximum (SUVmax), average (SUVmean), and total (SUVtotal) SUV. Linear mixed effects analysis was used to model the contribution of different scanning and patient characteristics to the reproducibility of various SUV measures. Fixed effects included average and difference in post-injection times, average and difference in injected dose, imaging site, scanner, lesion location, patient age, height, weight, and body mass index. Patient was included as a random effect. P-values resulting from the model were used to determine if a factor significantly impacted the repeatability of the imaging feature.
Results A total of 399 lesion ROIs were identified. Dose infiltration was minimal in all scans. SUVmean was most repeatable between scans (mean = 5.0%, std = 4.1%) and most influenced by difference between injected doses (p = 0.02), difference between post-injection times (p = 0.14), and lesion location (p = 0.11). SUVmax was less repeatable (mean = 10.7%, std = 8.9%) and most influenced by the difference between post-injection times (p = 0.04) and difference between injected doses (p = 0.14). SUVtotal was least repeatable (mean = 18.4%, std = 16.6%) and most influenced by difference between post-injection times (p = 0.08) and lesion location (p = 0.11). A deviation of 15 minutes in post-injection time attributed to a change in repeatability of SUVmean by 3.5%, of SUVmax by 9.0%, and SUVtotal by 15.3%. A deviation of 1.0 mCi in injected dose attributed to a change in repeatability of SUVmean by 4.6% and SUVmax by 5.8%; this factor was not significant for SUVtotal.
Conclusions In test-retest NaF PET/CT scans, inconsistencies in post-injection time and in injected dose were the two main factors degrading the repeatability of SUV measures. A lesion’s location in the body also impacted the quantitative repeatability of SUV.