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

BACKGROUND: In the development of new (18)F-labelled tracers, it is important to assess the amount of released [(18)F]fluoride taken up in the bones of experimental animals because all (18)F-labelled PET-tracers are prone, to lesser or higher degree, to undergo defluorination, with subsequent release of [(18)F]fluoride during scanning. However, the pharmacokinetics of [(18)F]fluoride in bones and other organs of healthy rats have not been well documented in a comprehensive manner. We aimed to study pharmacokinetics of [(18)F]NaF in rats in order to increase our understanding of the biodistribution of [(18)F]fluoride originating from defluorination of (18)F-labelled tracers. We studied [(18)F]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: [(18)F]fluoride perfusion and uptake varied among the different bones. [(18)F]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. CONCLUSION: Understanding the pharmacokinetics of [(18)F]fluoride in various bones and soft tissues is highly useful for assessing (18)F-labelled radiotracers that release [(18)F]fluoride. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13550-023-00969-4.