Performance of simplified methods for quantification of [18F]NaF uptake in fibrodysplasia ossificans progressiva

Fibrodysplasia Ossificans Progressiva (FOP) is a rare, genetic disease in which heterotopic bone is formed in muscles, tendons and ligaments throughout the body. Disease progression is variable over time and between individuals. 18F-fluoride uptake in newly formed bone can be evaluated using [18F]NaF (i.e., sodiumfluoride) PET/CT, identifying active areas of bone formation in FOP. The purpose of this study was to assess the performance of various semi-quantitative methods with full kinetic analysis.Seven patients (age range: 20–31 years) with FOP underwent dynamic [18F]NaF scans at baseline and after one year. [18F]NaF uptake was measured in aorta descendens, vertebrae, heterotopic bone lesions and metabolically active regions on PET, and quantified using nonlinear regression (NLR) analysis together with standardized uptake value (SUV) and target-to-blood ratio (TBR). SUV was on measured the 40–45 min frame of the dynamic sequence (SUV40–45) and on the subsequent static sweep (SUVStatic). Correlations between and SUV40–45 and NLR-derived Ki were comparable when normalized to body weight (r = 0.81, 95% CI 0.64–0.90), lean body mass (r = 0.79, 95% CI 0.61–0.89) and body surface area (r = 0.84, 95% CI 0.70–0.92). Correlation between TBR40–45 and NLR-derived Ki (r = 0.92, 95% CI 0.85–0.96) was higher than for SUV40–45. Correlation between TBR40–45 and NLR-derived Ki was similar at baseline and after one year (r = 0.93 and 0.94). The change in TBR40–45 between baseline measurement and after one year correlated best with the change in NLR-derived Ki in the PET-active lesions (r = 0.87).The present data supports the use of TBR for assessing fluoride uptake in PET-active lesions in FOP.Sub-study of the Lumina-1 trial (clinicaltrials.gov, NCT03188666, registered 13-06-2017).