Acronym for positron emission tomography, a medical test that is especially useful in showing how tissue or an organ is functioning, as opposed to just showing structure. In a PET scan, radioactive atoms are introduced into the body, where their chemical behavior is exactly the same as similar nonradioactive atoms. The positrons emitted when these nuclei decay collide with electrons in surrounding tissue, producing gamma rays that can then be detected by instruments outside the body.

Note: A PET scan can show the blood flow through the brain, areas of high metabolic activity that indicate potential tumors, as well as areas of damaged heart tissue.

PET scan (pět)
n.
A cross-sectional image produced by a PET scanner.