Comparison of different quantitative approaches to¹⁸F-fluoride PET scans

The aim of this study was to evaluate the relationship between ¹⁸F-fluoride bone metabolic measures obtained by nonlinear regression (NLR), Patlak analysis, and standardized uptake value (SUV) for a wide range of normal and pathologic bone conditions. In patients imaged twice, changes in metabolic rates were determined using the different quantitation methods. Methods: In 33 patients 2-51 mo after resection of a bone tumor of the limbs, a total of 42 dynamic PET scans were performed after injection of 250-350 MBq ¹⁸F-fluoride. SUV, fluoride bone influx rate obtained by Patlak analysis (K_Pat), and fluoride bone influx rate obtained by NLR (K_NLR) were calculated in each patient for the bone graft, the contralateral normal side, and the spine, if within the field of view. Results: SUV ranged from 0.4 to 9.9, K_Pat from 0.0035 to 0.0742 mL/min/mL, and K_NLR from 0.0027 to 0.0737 mL/min/mL. Significant linear correlations were found between K_Pat and K_NLR (r 0.99), K_Pat and SUV (r = 0.95), and K_NLR and SUV (r = 0.93). Eight patients have been imaged twice within 6 mo. Changes in metabolic values of the grafts were significantly correlated for K_Pat and K _NLR (r = 0.96), K_Pat and SUV (r = 0.88), and K _NLR and SUV (r = 0.79). The 95% ranges of normal change in limb bones were ±58.0% for SUV, ±23.0% for K_Pat, and ±20.2% for K_NLR; the corresponding 95% ranges in the spine were ±8.6%, ±7.6%, and ±19.6%. Conclusion: The results of this study show that ¹⁸F-fluoride metabolic values as well as changes in bone metabolism measured by SUV and Patlak analysis were strongly correlated with NLR findings. The high 95% range of normal change of SUV in limb bones, however, indicates that this parameter is of limited value in areas with low metabolic activity. The range of spontaneous bone metabolic rate fluctuations presented in this study may be used as an estimate for assessing changes in bone metabolic activity, and the normal values for limb bones provide a basis for further studies on ¹⁸F-fluoride bone metabolism.