What Is a PET Scan Used For?

A PET scan — Positron Emission Tomography — is a specialized nuclear medicine imaging technique that measures metabolic activity in the body's tissues rather than their physical structure. While CT and MRI reveal anatomy (what things look like), PET reveals physiology (how things are functioning at the cellular level). This functional perspective makes PET an extraordinarily valuable tool for detecting cancer, evaluating brain disorders, and assessing heart disease in ways that structural imaging alone cannot match.

How Pet Scanning Works

PET imaging relies on a radioactive tracer — most commonly a molecule called FDG (fluorodeoxyglucose), which is glucose (sugar) labeled with a radioactive fluorine atom (fluorine-18). The patient receives an intravenous injection of this tracer, and waits approximately 60 minutes for it to distribute throughout the body.

Cancer cells — and some other highly metabolically active cells — consume glucose at a much higher rate than normal cells. Because FDG behaves like glucose, it is absorbed preferentially by these high-activity cells. The fluorine-18 within FDG is a positron emitter: as it undergoes radioactive decay, it releases positrons (the antimatter counterpart of electrons). Each positron immediately collides with a nearby electron and annihilates, producing two gamma rays traveling in exactly opposite directions.