Definition of PET scan:

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

How the test is performed:

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.

How to prepare for the test:

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.

How the test will feel:

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.

Why the test is performed:

A PET scan can reveal the size, shape, position, and some function of organs, so your doctor can make sure they are working as well as they should.

This test can be used to diagnose cancer, heart problems, and brain disorders. It can see how far cancer has spread, show areas in which there is poor blood flow to the heart, and check brain function.

Several PET scans may be taken to determine how well you're responding to treatment for cancer or another illness.