Evaluating knee inflammation and bone turnover in rheumatoid arthritis with FDG- and NaF-PET/CT

1166 Objectives: Rheumatoid arthritis (RA) involves chronic inflammation of synovial joints, causing pain, stiffness, and limited mobility. 18F-sodium fluoride (NaF) is a PET tracer whose uptake reflects bone turnover, while 18F-fludeoxyglucose (FDG) shows glucose metabolism and can serve as a marker for inflammation. The aim of this study was to determine the feasibility of calculating the FDG and NaF mean standardized uptake value (SUVmean) in the knees of RA patients and to evaluate the construct validity of these parameters.Methods: Prospective FDG-PET/CT as well as NaF-PET/CT imaging was performed on 18 RA patients. The superoinferior anatomical boundaries of the knee were defined as 4 cm above and below the intercondylar eminence. CT segmentation with a lower threshold of 150 HU and upper threshold of 1500 HU was performed on the coregistered PET/CT image, followed by morphological closing with an element radius of 20. The SUVmean was calculated separately for left and right knees on FDG-PET/CT and NaF-PET/CT images. Paired t-tests were used to determine differences in uptake between left and right knees. Linear regressions were used to compare averaged left and right PET parameters with clinical data.Results: FDG and NaF uptake were found to be significantly correlated (r = 0.77, p Conclusions: The quantification of FDG uptake and NaF uptake in the knee was found to be feasible using CT segmentation. No lateral bias in uptake was observed, which is consistent with the often symmetric involvement of joints in RA. However, neither PET parameter was associated with traditional markers of systemic inflammation. Rather, both NaF SUVmean and FDG SUVmean were correlated with clinical variables related to body weight and fat content, suggesting that degenerative joint disease may play a larger role in influencing the uptake of these tracers than RA disease activity. Larger prospective and longitudinal data are necessary to gain a better understanding of the roles of FDG and NaF in evaluating RA.