Positron emission tomography (PET) is an imaging test that uses a radioactive substance (called a tracer) to look for disease in the body. Unlike magnetic resonance imaging (MRI) and computed tomography (CT) scans, which reveal the structure of organs, a PET scan shows how the organs and tissues are functioning.

See also:

• Bone scan
• Lung scan
• Nuclear ventriculography
• Pulmonary ventilation/perfusion scan
• Renal scan
• Thyroid scan

Nuclear medicine scan; Positron emission tomography

PET scans use a small amount of a radioactive substance injected into a vein, usually on the inside of the elbow. The substance travels through the blood and collects in organs or tissues.

You will be scanned approximately 60 minutes after receiving the radioactive substance. You lie on a table that slides into a tunnel-shaped hole in the center of the PET scanner.

The PET machine detects energy given off by the radioactive substance and converts it into 3-dimensional pictures. The images are sent to a computer, where they are displayed on a monitor for the physician to read.

You must lie still during the PET scan so that the machine can get clear images of your organs. The test takes about 30 minutes.

You must sign a consent form before having this test. You will be told not to eat anything for 4 - 6 hours before the PET scan, although you will be able to drink water.

Tell your doctor if you are pregnant or think you might be pregnant.

Also tell your doctor about any prescription and over-the-counter medicines that you are taking, because they may interfere with the test.

Be sure to mention if you have any allergies, or if you've had any recent imaging studies using injected dye (contrast).

During the test, you may need to wear a hospital gown. Take off any jewelry, dentures, and other metal objects because they could affect the scan results.

You will feel a sharp prick when the needle with the radioactive substance is inserted into your vein. You shouldn't feel anything during the actual PET scan.