PET Scan: Positron Emission Tomography

This test makes images that show activity in body tissues. A substance that gives off a tiny amount of radiation is put into your body. This substance goes to the part of your body that is most active. A machine can then detect where that substance is. PET can be done for many body parts, including:

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PET Scans of the Brain
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The Purpose of a PET Scan  

A PET scan may be done for a number of reasons, including:

  • Looking for tumors or assessing tumor level of activity after treatment
  • Assessing causes of memory disorders
  • Finding the cause of seizures and helping to find treatments
  • Assessing brain metabolism in patients with chronic fatigue syndrome
  • Looking for heart disease

Prior to a PET Scan

Check with your doctor about your current medications. Make sure to let your doctor know about any allergies or unrelated illnesses you may have, or if you are pregnant. Some people have a bad reaction to the contrast dye, allergic reactions or kidney problems. Also:

  • Wear comfortable clothes.
  • Do not eat or drink anything, except water, for at least four hours before the scan.

Description of a PET Scan

You will be given a radioactive substance through an injection. It will travel through your blood to the area of the body being studied. It takes 30-90 minutes for the substance to be absorbed by the tissue. When the substance has been absorbed, the scan can take place.

You will lie on a table and be moved into a machine that looks like a large, square doughnut. This machine detects and records the energy levels from the substance that was injected earlier. The images are viewed on a computer monitor. The scan lasts about 30-45 minutes. You may be asked to perform specific tasks before or during the test. For example, during a heart PET scan, you may be asked to walk on a treadmill.

Except for the pinprick from the injection, a PET scan is a painless procedure. People who are uncomfortable in closed or tight spaces may have some anxiety.

After the test, drink plenty of fluids to help the radioactive substance pass from your body.

PET Scan Results   

The images will show activity levels as different colors or degrees of brightness. A radiologist will review the images and send the results to your doctor. It may take a few days for your doctor to receive the report.

When to Call Your Doctor    

Call your doctor if you have any unusual symptoms such as a rash, itching or difficulty breathing. These symptoms may mean that you're having an allergic reaction to the radioactive substance.


Content was created using EBSCO’s Health Library. Edits to original content made by Rector and Visitors of the University of Virginia. This information is not a substitute for professional medical advice.