Positron emission tomography (PET) scan is a test that combines computed tomography (CT) and nuclear scanning. During a PET scan, a radioactive substance called a tracer is combined with a chemical (such as glucose); this mixture is generally injected into a vein (usually in the arm) but on occasion may be inhaled.

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

Compared to CT scans and magnetic resonance imaging (MRI), the pictures from a PET scan do not show as much detail.