All three Oxygen isotopes have medical applications. O-16 is used in the production of radioactive N-13 which is used for PET imaging and myocardial perfusion. O-17 can be used as a tracer in the study of cerebral oxygen utilization. Large quantities of O-18 are used for the production of F-18. F-18 is used to produce 2-[18F] fluoro-2-deoxyglucose (FDG) which is used as a tracer in positron emission tomography or PET. Millions of these FDG-PET medical procedures are performed annually to investigate a range of diseases in various human organs.