Figure 1. FDG (fluorodeoxyglucose) Molecule. A radioactive label or tag called Fluorine 18 (F18) is produced in a cyclotron. It is added to molecules that cells utilize in their metabolism; in the case of FDG, the “parent” molecule is glucose. The F18 replaces an oxygen molecule resulting in fluorodeoxyglucose. The clinician usually orders this test as a 18F-FDG PET/CT scan.