Positron emission tomography (PET) is a test that uses a special type of camera and a tracer (radioactive substance) to look at organs in the body.

During a PET scan, the tracer is typically injected into a vein (usually in the arm), but sometimes it may be inhaled. The tracer usually is a special form of a substance (such as glucose) that can be used (metabolized) by cells in the body.

A PET scan is often used to evaluate cancer, such as of the lung or colon. It also can be used to evaluate the heart's metabolism and blood flow and examine brain function.

PET scan pictures do not show as much detail as computed tomography (CT) scans or magnetic resonance imaging (MRI).