Positron emission tomography (PET) is a radioactive technique. It produces maps of metabolically active processes occurring in specific locations in a living body. A radioactive tracer bound to a sugar molecule is injected into a living patient. As the radioisotope decays a positron is emitted. Positrons are the antimatter components of electrons. When a positron collides and annihilates with an electron the gamma photons generated are detected.

PET scans provide physiological rather than anatomical data.