[F-18]Fluoride uptake in various bone types and soft tissues in rat

BackgroundIn the development of new F-18-labelled tracers, it is important to assess the amount of released [F-18]fluoride taken up in the bones of experimental animals because all F-18-labelled PET-tracers are prone, to lesser or higher degree, to undergo defluorination, with subsequent release of [F-18]fluoride during scanning. However, the pharmacokinetics of [F-18]fluoride in bones and other organs of healthy rats have not been well documented in a comprehensive manner. We aimed to study pharmacokinetics of [F-18]NaF in rats in order to increase our understanding of the biodistribution of [F-18]fluoride originating from defluorination of F-18-labelled tracers. We studied [F-18]fluoride uptake in Sprague Dawley rat bones, including the epiphyseal parts of the tibia and radius, the mandible, ilium, lumbar vertebrae, costochondral joints, tibia, radius, and ribs, with 60-min in vivo PET/CT imaging. Kinetic parameters, K-1, K-i, K-i/K-1, and k(3) were calculated with a three-compartment model. In addition, separate groups of male and female rats were studied with ex vivo bone and soft tissue harvesting and gamma counting over a 6-h period.Results[F-18]fluoride perfusion and uptake varied among the different bones. [F-18]fluoride uptake was higher in trabecular bones, due to high perfusion and osteoblastic activity, compared to cortical bones. In soft tissues, the organ-to-blood uptake ratios increased over time in the eyes, lungs, brain, testes, and ovaries during the 6 h study period.ConclusionUnderstanding the pharmacokinetics of [F-18]fluoride in various bones and soft tissues is highly useful for assessing F-18-labelled radiotracers that release [F-18]fluoride.