Fluorine-18 is one of the early tracers used in positron emission tomography (PET), having been in use since the 1960s.
Its significance is due to both its short half-life and the emission of positrons when decaying. 
A major medical use of fluorine-18 is: in positron emission tomography (PET) to image the brain and heart; to image the thyroid gland; as a radiotracer to image bones and seeking cancers that have metastasized from other locations in the body and in radiation therapy treating internal tumors.
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 (FDG), where the F substitutes a hydroxyl.
New dioxaborolane chemistry enables radioactive fluoride (F) labeling of antibodies, which allows for positron emission tomography (PET) imaging of cancer. A uman-erived, enetic, ositron-emitting and luorescent (HD-GPF) reporter system uses a human protein, PSMA and non-immunogenic, and a small molecule that is positron-emitting (F) 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. The dual-modality small molecule targeting PSMA was tested in humans and found the location of primary and metastatic prostate cancer, fluorescence-guided removal of cancer, and detects single cancer cells in tissue margins.