Fluorine18

Fluorine-18 (18F) is a radioactive isotope of fluorine used primarily in diagnostic imaging with positron emission tomography (PET). It decays by positron emission to stable oxygen-18, with a half-life of about 109.8 minutes. The emitted positrons annihilate with electrons to produce two 511 keV gamma photons, which are detected in PET to create images of tracer distribution.

18F is produced in cyclotrons by irradiating 18O-enriched water with protons, using the 18O(p,n)18F reaction at typically 10–20 MeV. The resulting [18F]fluoride is recovered in aqueous solution and then incorporated into target molecules via nucleophilic substitution, often after complexation with cryptand reagents to form reactive fluoride species for labeling.

Among radiopharmaceuticals, 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is by far the most widely used tracer, reflecting cellular glucose metabolism. FDG is transported into cells and phosphorylated, becoming trapped, which highlights regions of high metabolic activity such as many cancers, as well as certain brain and heart conditions.

Other 18F tracers include [18F]fluorodopa for dopaminergic imaging, [18F]FLT for proliferation, [18F]FMISO for hypoxia, and [18F]NaF for bone imaging. The choice of tracer depends on the clinical question and imaging strategy.

Safety and logistics considerations include programs for radiopharmaceutical production, quality control, and radiation protection. Because of the relatively short half-life, patient radiation exposure is limited in time, and PET imaging with 18F-based tracers is conducted in specialized facilities following regulatory guidelines.