High molar activity [18F]Tetrafluoroborate synthesis for Sodium Iodide Symporter imaging by PET.

Abstract Background. Sodium iodide symporter (NIS) imaging by positron emission tomography is gaining traction in nuclear medicine, with a number of human studies recently published using fluorine-18 labelled tetrafluoroborate ([18F]TFB). Clinical success of any radiotracer relies heavily on its accessibility, which in turn depends on the availability of robust radiolabelling procedures providing a radiotracer in large quantities and of high radiopharmaceutical quality. Results. Here we publish improved radiolabelling of and quality control procedures for [18F]TFB with high molar activity. The use of ammonium hydroxide for [18F]fluoride elution, of commercially available boron trifluoride-solvent complex as precursor and removal of unreacted [18F]fluoride on Florisil solid-phase extraction cartridges resulted in the reliable production of [18F]TFB on SYNTHRA and FX-FN automated synthesizers with radiochemical yields in excess of 30%, radiochemical purity in excess of 98% and molar activities in the range of 35 -217 GBq/μmol at the end of synthesis. Conclusions. A novel automated radiosynthesis procedure for [18F]tetrafluoroborate has been developed that provides radiotracer with high molar activity. PET scanning of a mouse lung tumour model carrying an NIS reporter gene rendered images of high quality and improved sensitivity.