Positron Emission Tomography
by Editorial Staff and Contributors
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:
Reasons for Test
A PET scan may be done for a number of reasons, including:
Complications are rare. If you are planning to have a PET scan, your doctor will review a list of possible complications.
Some people have a bad reaction to the contrast dye. The contrast is the chemical that improves the details in the pictures. In some people, the contrast 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 if you 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
Description of Test
You will be given a radioactive substance. This may be done through an injection, or in some cases, you will be asked to breathe in a gas. 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.
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 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.
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:
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Updated November 2, 2015. Accessed October 3, 2017.
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. Updated January 23, 2017. Accessed October 3, 2017.
Positron emission tomography (PET scan). Cleveland Clinic website. Available at: https://my.clevelandclinic.org/health/articles/pet-scan. Updated February 23, 2009. Accessed October 3, 2017.
Positron emission tomography (PET scan). Johns Hopkins Medicine website. Available at:
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Accessed October 3, 2017.
Last reviewed September 2018 by EBSCO Medical Review Board Daus Mahnke, MD
Last Updated: 9/5/2014
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