What isotope is used in the injection for a pet scan?

PET scan. It depends on the question being asked. Cardiac pet scans use several different types of isotopes including rubidium-82, n-13 ammonia, and fluorine-18 deoxyglucose. These can be used to measure myocardial metabolism (fluorine-18 deoxyglucose) or coronary blood flow (rubidium-82, n-13 ammonia).
Generally F-18. The p in pet stands for positron - all isotopes used in pet have to be positron emitters. The most common isotope used in pet today is f-18 fluorine. It has an half life of 110 minutes, and is most frequently chemically incorporated with glucose as f-18 fluorodeoxyglucose, or f-18 fdg, which distributes in cells based on glucose metabolism (or consumption).