Differences in skeletal kinetics between vertebral and humeral bone measured by F-18-fluoride positron emission tomography in postmenopausal women

We have sought to investigate regional differences in skeletal kinetics bet ween lumbar vertebrae and the humerus of postmenopausal women with F-18-flu oride positron emission tomography (PET). Twenty-six women, mean age 62 yea rs, had dynamic PET scans of the lumbar spine and lower humerus after the i njection of 180 MBq F-18-fluoride ion. Plasma arterial input functions (IFs ) were calculated from a mean IF measured arterially from 10 women and scal ed according to late individual venous activity. Vertebral and humeral time activity curves were measured by placing regions of interest (ROI) over lu mbar vertebrae and the humeral shaft. Using a three-compartmental model and nonlinear regression analysis the macroconstant Ki, representing plasma cl earance of fluoride to bone mineral, and the individual rate constants K1 ( related to regional skeletal blood flow) and k2 to k4 describing transport between plasma, an extracellular fluid compartment and a bone mineral compa rtment, were measured. Mean vertebral Ki (3.47 x 10(-2) mi min-l ml-l) and K1 (1.08 x 10(-1) ml.min(-1) ml(-1)) were found to be significantly greater than humeral Ki (1.64 x 10(-2) mi min-l ml-l; P < 0.0001) and K1 (3.90 x 1 0(-2) ml.min(-1) ml(-1); P < 0.0001) but no significant differences were fo und in k2, k3, and k4. These findings confirm differences in regional skele tal kinetics between lumbar vertebrae and the lower humerus. These observat ions may help increase our understanding of the regional differences in pat hophysiology and response to treatment that have been observed in sites con sisting predominantly of either trabecular or cortical bone. F-18-fluoride PET may prove to be a valuable technique in the noninvasive measurement of regional skeletal metabolism.