Positron Emission Tomography



This test makes images that show areas of active disease. It uses a substance that is radioactive and is attracted to areas of disease. When the scan takes images, the areas of disease will be highlighted.

PET Scans of the Brain

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Reasons for Test

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 those with chronic fatigue syndrome
  • Looking for heart disease

Possible Complications

Problems are rare. The doctor will talk about possible problems such as:

  • Bad reaction to the substance. In some people, it can cause allergic reactions or kidney problems.
  • A PET scan does use radiation. You and your doctor will weigh the harms and benefits of this test. A PET scan may not be advised for people who are pregnant.

Be sure to discuss these risks with your doctor before the test. Let your doctor know about any allergies or unrelated illnesses you may have.

What to Expect

Prior to Test

The care team may discuss:

  • No food or drink, except water, for at least 4 hours before the scan.
  • Regular medications, some may need to be stopped before test.
  • Specific diet changes if you have diabetes.

Wear comfortable clothes to the test but you may be asked to wear a hospital gown. Tell the care team if you are pregnant or breastfeeding.

Description of Test

You will be given a radioactive substance. It may be given as an injection or you will take it by mouth or inhale it into the lungs. This will deliver to substance to area that is being studied. It takes 30 to 90 minutes for the substance to be absorbed by the tissue. You will rest while this takes place.

The machine looks like a large donut. A table will slide in and out of the opening. You will lie on a table. A technician will move the table into position. This machine can make clicking sounds during the test. The images are viewed on a computer monitor. The scan lasts about 30 to 45 minutes. You may be asked to move or do other tasks during the test. For example, during a heart PET scan, you may be asked to walk on a treadmill.

After Test

Drink plenty of fluids to help the radioactive substance pass from your body.

How Long Will It Take?

At least 2 hours

Will It Hurt?

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.


The images will show activity levels as different colors or 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.

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 are having an allergic reaction to the radioactive substance.


Family Doctor—American Academy of Family Physicians
Radiology Info—Radiological Society of North America


The College of Family Physicians of Canada


PET scan. NHS Choices website. Available at:
...(Click grey area to select URL)
Accessed October 3, 2020.
Positron emission tomography—computed tomography (PET/CT). Radiology Info—Radiological Society of North America website. Available at: https://www.radiologyinfo.org/en/info.cfm?pg=pet. Accessed October 3, 2020.
Positron emission tomography (PET scan). Cleveland Clinic website. Available at: https://my.clevelandclinic.org/health/articles/pet-scan. Accessed October 3, 2020.
Positron emission tomography (PET scan). Johns Hopkins Medicine website. Available at:
...(Click grey area to select URL)
Accessed October 3, 2020.
Last reviewed October 2020 by EBSCO Medical Review Board Daus Mahnke, MD
Last Updated: 09/05/2020

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