The acute effect of loading on bone tissue and physiology can offer important information with regard to joint function in diseases such as osteoarthritis. Therefore Imaging studies using [18F]-sodium fluoride ([18F]NaF) ;have found changes in tracer kinetics in animals after subjecting bones to strain, indicating an acute physiological response. The aim of this study is to measure acute changes in NaF uptake in human bone due to exercise-induced loading.Twelve healthy subjects underwent two consecutive 50-min [18F]NaF PET/MRI examinations of the knees, one baseline followed by one post-exercise scan.
[18F]NaF PET/MRI examinations
Quantification of tracer kinetics is perform using an image-derived input function from the popliteal artery. For both scans; kinetic parameters of KiNLR, K1, k2, k3, and blood volume are mapp para metrically using nonlinear regression with the Hawkins model. The kinetic parameters along with mean SUV and SUVmax are compare between the pre and post-exercise examinations. Differences in response to exercise are analyse between bone tissue types (subchondral, cortical, and trabecular bone) and between regional subsections of knee subchondral bone.
Acute loading of bone tissue is thought to stimulate bone formation and is of growing interest clinically and in the study of bone physiology. Abnormal bone physiology is not only a key element in joint disease and osteoporosis; but skeletal fragility is directly related to mortality and risk of fracture. Studies of bone adaptation to loading have shown that stress on bone cells and strain-mediated fluid flow are crucial in regulating bone metabolism. However; the acute response of loading in bone is still poorly understood and difficult to measure in humans in vivo.
Stimulate bone formation
Molecular information from PET has shown promise in early detection of metabolic abnormalities of bone metabolism in osteoarthritis ; associations to bone pain , and early indication of bone degradation in diseases such as osteoarthritis and osteoporosis. PET has also been use to demonstrate changes in glucose uptake and blood flow in bone marrow in response to exercise loading. [18F]-sodium fluoride ([18F]-NaF); is a well-established bone-seeking agent which may serve as a marker to study bone turnover.
In particular, kinetic modeling of dynamic [18F]NaF uptake can quantify bone physiology including bone perfusion (K1); bone mineralization (k3); and tracer plasma clearance (Ki). Animal studies have shown both an acute hyperemia and a large increase in [18F]-NaF standard uptake values (SUV) in response to acute loading; which lasts up to 7 days after loading . Furthermore, this response has been positively correlate with the force intensity of the applied load on the bone. The dynamics of [18F]NaF uptake after acute bone loading have not been reported in humans. To date; human studies of bone adaptation to loading have been based on changes in structure and mineral density over periods of weeks and months of high-impact exercise.