Positron emission tomography, also called PET scan, is a diagnostic test that involves the acquisition of physiologic images based on the detection of positrons emitted from a radioactive substance administered to the patient.

PET scans are used most often to detect cancer and to examine the effects of therapy.

Before a scan the patient goes to a special room where the radioactive substance is administered. It will take about 30 to 90 minutes for the substance to travel through the body and accumulate in the tissues under study.

The PET scanner, has a hole in the middle and looks like a large doughnut. Within are multiple rings of detectors that record the emission of energy. While lying on the exam table, the patient is moved into the hole of the machine.The scan usually takes about 30 to 45 minutes

Note: The image shown here is of a PET scan machine with the superimposed image of a scan (in the lower right-hand corner of the image).