Differences in regional bone perfusion and turnover between lumbar spine and distal humerus: (18)F-fluoride PET study of treatment-naïve and treated postmenopausal women.

The functional imaging technique of (18)F-fluoride positron emission tomography ((18)F-PET) allows the non-invasive assessment of regional bone blood perfusion and turnover. Bone perfusion and turnover measured using (18)F-PET correlate closely with those obtained experimentally and so they can be readily applied in clinical research studies. The aim of this study was to compare bone perfusion and turnover between the lumbar spine and humerus in both treatment naïve postmenopausal women (n=11) and those on stable antiresorptive therapy (n=12). All women had a BMD T-score of less than -2 at the spine and/or hip. Each woman had a dynamic PET scan of the lumbar spine and distal humerus after injection of 90 MBq (18)F-fluoride. Using a three-compartmental model bone perfusion (K(1)), the net plasma clearance of tracer to bone mineral (K(i)) reflecting regional bone turnover and the rate constants k(2)-k(4) describing the transport of fluoride between plasma, an extravascular bone compartment and bone mineral compartment were calculated. Mean bone perfusion (K(1)) and bone turnover (K(i)) were significantly higher at the lumbar spine compared to the humerus for both treatment-naïve and antiresorptive groups. K(1) values were on average 3 times greater while K(i) was approximately 50% greater at the lumbar spine. The rate constant k(2), the reverse transport of fluoride from the extravascular compartment to plasma, was significantly lower at the humerus compared to the lumbar spine in both groups. The ratio K(i)/K(1) describing the unidirectional extraction efficiency to bone mineral was significantly greater at the humerus compared to the lumbar spine for both study groups. No significant differences between skeletal sites were observed for k(3) or k(4). In conclusion a significant skeletal heterogeneity was observed in terms of bone perfusion and turnover between the lumbar spine and humerus. (18)F-PET may aid in our understanding of the importance of bone perfusion in osteoporosis and differences in regional bone turnover with disease and in response to therapy.