Oxygen-18

Oxygen-18 (¹⁸
O, Ω) is a natural, stable isotope of oxygen and one of the environmental isotopes.

¹⁸
O is an important precursor for the production of fluorodeoxyglucose (FDG) used in positron emission tomography (PET). Generally, in the radiopharmaceutical industry, enriched water (H
₂Ω) is bombarded with hydrogen ions in either a cyclotron or linear accelerator, producing fluorine-18. This is then synthesized into FDG and injected into a patient. It can also be used to make an extremely heavy version of water when combined with tritium (hydrogen-3): ³
H
₂¹⁸
O or T
₂Ω. This compound has a density almost 30% greater than that of natural water.

The accurate measurements of ¹⁸
O rely on proper procedures of analysis, sample preparation and storage.