Correcting 18F-fluoride PET static scan measurements of skeletal plasma clearance for tracer efflux from bone

ObjectiveThe aim of the study was to examine whether F-18-fluoride PET (F-18-PET) static scan measurements of bone plasma clearance (K-i) can be corrected for tracer efflux from bone from the time of injection.Materials and methodsThe efflux of tracer from bone mineral to plasma was described by a first-order rate constant k(loss). A modified Patlak analysis was applied to 60-min dynamic F-18-PET scans of the spine and hip acquired during trials on the bone anabolic agent teriparatide to find the best-fit values of k(loss) at the lumbar spine, total hip and femoral shaft. The resulting values of k(loss) were used to extrapolate the modified Patlak plots to 120 min after injection and derive a sequence of static scan estimates of K-i at 4-min intervals that were compared with the Patlak K-i values from the 60-min dynamic scans. A comparison was made with the results of the standard static scan analysis, which assumes k(loss)=0.ResultsThe best-fit values of k(loss) for the spine and hip regions of interest averaged 0.006/min and did not change when patients were treated with teriparatide. Static scan values of K-i calculated using the modified analysis with k(loss)=0.006/min were independent of time between 10 and 120 min after injection and were in close agreement with findings from the dynamic scans. In contrast, by 2 h after injection the static scan K-i values calculated using the standard analysis underestimated the dynamic scan results by 20%.ConclusionUsing a modified analysis that corrects for F-18 efflux from bone, estimates of K-i from static PET scans can be corrected for time up to 2 h after injection. This simplified approach may obviate the need to perform dynamic scans and hence shorten the scanning procedure for the patient and reduce the cost of studies. It also enables reliable estimates of K-i to be obtained from multiple skeletal sites with a single injection of tracer. (C) 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins.