Assessment of the metabolic activity of bone grafts with 18F-fluoride PET

Purpose. The aims of this prospective study were to evaluate quantitative approaches to F-18-fluoride positron emission tomography (PET) imaging in allogenic bone grafts of the limbs, and to assess the time course of graft healing after surgery. Methods. We performed a total of 52 dynamic F-18-fluoride PET studies in 34 patients with cancellous and full bone grafts. Seven patients were imaged three times at 6, 12, and 24 months after surgery, and four patients were imaged twice. PET data were quantitatively analyzed using non-linear regression (NLR) analysis, Patlak analysis, and standardized uptake value (SUV). Results. Fluoride bone metabolism in cancellous grafts decreased by 25% from 6 to 12 months post surgery, and revealed a total decrease of 60-65% after 2 years for SUV, K-Pat, and K-NLR. Full bone grafts first showed an increase by 20% from 6 to 12 months and from then on decreased to 70% of the initial activity at the end of 2 years with either quantification method. In two patients with non-union of their full bone grafts, increases in SUV, K-Pat, K-NLR, and K-1 far above average and outside the normal time pattern were observed. Highly significant correlations were found between SUV, K-Pat, K-NLR, and K-1 for both grafts and normal limb bones. In patients imaged repeatedly, the percentage changes in fluoride graft metabolism were also significantly correlated between SUV, K-Pat, and K-NLR. Conclusion. Quantitative F-18-fluoride PET is a promising tool for assessment of fluoride metabolism and normal healing in bone grafts of the limbs.