scroll to top
Loading icon
Health Information Center
Press enter or spacebar to select a desired language.

Positron Emission Tomography

  • Editorial Staff and Contributors
Publication Type:


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

Nucleus factsheet image factsheet imageNULL\\filer01a\Intellect\images\exh4473a_ma.jpgNULL14NULL2004-05-24234390Copyright © Nucleus Medical Media, Inc.

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 go over some problems such as:

  • A bad reaction to the substance. In some people, it can cause allergic reactions or kidney problems.
  • Radiation exposure. A PET scan may not be advised for people who are pregnant.

Risks should be discussed with the doctor before the test.

What to Expect

Prior to Test

The care team may meet with you to talk about:

  • Fasting such as avoiding food and drink for a period of time before the test.
  • Any allergies you may have
  • Current medicines, herbs, and supplements that you take and whether you need to stop taking them before the 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 by injection, by mouth, or inhaled into the lungs. It takes 30 to 90 minutes for the substance to be absorbed by the tissue. You will rest while this takes place.

You will lie on a table. The 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?

No, except for the pinprick from the injection. Some people have anxiety in tight or closed places.


The images will show disease activity levels. It will show 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.

Problems to Look Out For

Call your doctor if you have any unusual symptoms such as a rash, itching, or problems breathing. These may be signs of an allergic reaction to the radioactive substance.





  • Kwon DH, Velazquez AI, de Kouchkovsky I. PSMA PET Scan. JAMA Oncol. 2022;8(12):1860.
  • PET scan. NHS Choices website. Available at:
  • Positron emission tomography—computed tomography (PET/CT). Radiology Info—Radiological Society of North America website. Available at:
  • Positron emission tomography (PET scan). Cleveland Clinic website. Available at:
  • Positron emission tomography (PET scan). Johns Hopkins Medicine website. Available at:
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.