Fluorine-18


Fluorine-18 is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380 u and its half-life is 109.771 minutes. It decays by positron emission 97% of the time and electron capture 3% of the time. Both modes of decay yield stable oxygen-18.

Synthesis

In the radiopharmaceutical industry, fluorine-18 is made using either a cyclotron or linear particle accelerator to bombard a target, usually of pure or enriched water with high energy protons. The fluorine produced is in the form of a water solution of fluoride, which is then used in a rapid chemical synthesis of the radiopharmaceutical. The organic oxygen-18 pharmaceutical molecule is not made before the production of the radiopharmaceutical, as high energy protons destroy such molecules. Radiopharmaceuticals using fluorine must therefore be synthesized after the fluorine-18 has been produced.

Chemistry

Fluorine-18 is often substituted for a hydroxyl group in a radiotracer parent molecule, due to similar steric and electrostatic properties. This may however be problematic in certain applications due to possible changes in the molecule polarity.

Applications

Fluorine-18 is one of the early tracers used in positron emission tomography, having been in use since the 1960s.
Its significance is due to both its short half-life and the emission of positrons when decaying.
Tracers include sodium fluoride which can be useful for skeletal imaging as it displays high and rapid bone uptake accompanied by very rapid blood clearance, which results in a high bone-to-background ratio in a short time and
fluorodeoxyglucose, where the 18F substitutes a hydroxyl.
New dioxaborolane chemistry enables radioactive fluoride labeling of antibodies, which allows for positron emission tomography imaging of cancer. A Human-Derived, Genetic, Positron-emitting and Fluorescent reporter system uses a human protein, PSMA and non-immunogenic, and a small molecule that is positron-emitting and fluorescent for dual modality PET and fluorescence imaging of genome modified cells, e.g. cancer, CRISPR/Cas9, or CAR T-cells, in an entire mouse.