Long-term precision of 18F-fluoride PET skeletal kinetic studies in the assessment of bone metabolism

F-18-Fluoride PET allows noninvasive evaluation of regional bone metabolism and has the potential to become a useful tool for assessing patients with metabolic bone disease and evaluating novel drugs being developed for these diseases. The main PET parameter of interest, termed K-i, reflects regional bone metabolism. The aim of this study was to compare the long-term precision of F-18-fluoride PET with that of biochemical markers of bone turnover assessed over 6 mo. Methods: Sixteen postmenopausal women with osteoporosis or significant osteopenia and a mean age of 64 y underwent F-18-fluoride PET of the lumbar spine and measurements of biochemical markers of bone formation (bone-specific alkaline phosphatase and osteocalcin) and bone resorption (urinary deoxypyridinoline) at baseline and 6 mo later. Four different methods for analyzing the F-18-fluoride PET data were compared: a 4k 3-compartmental model using nonlinear regression analysis (Ki-4k), a 3k 3-compartmental model using nonlinear regression analysis (Ki-3k), Patlak analysis (Ki-PAT), and standardized uptake values. Results: With the exception of a small but significant decrease in K(i-3)k at 6 mo, there were no significant differences between the baseline and 6-mo values for the PET parameters or biochemical markers. The long-term precision, expressed as the coefficient of variation (with 95% confidence interval in parentheses), was 12.2% (9%-19%), 13.8% (10%-22%), 14.4% (11%-22%), and 26.6% (19%-40%) for Ki-3k, Ki-PAT, mean standardized uptake value, and Ki-4k, respectively. For comparison, the precision of the biochemical markers was 10% (7%-15%), 18% (13%-27%), and 14% (10%-21%) for bone-specific alkaline phosphatase, osteocalcin, and urinary deoxypyridinoline, respectively. Intraclass correlation between the baseline and 6-mo values ranged from 0.44 for Ki-4k to 0.85 for Ki-3k. No significant correlation was found between the repeated mean standardized uptake value measurements. Conclusion: The precision and intraclass correlation observed for Ki-3k and Ki-PAT was equivalent to that observed for biochemical markers. This study provided initial data on the long-term precision of F-18-fluoride PET measured at the lumbar spine, which will aid in the accurate interpretation of changes in regional bone metabolism in response to treatment.