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PET/CT scan is a type of imaging test that combines positron emission tomography (PET) and computed tomography (CT) techniques. Combined PET/CT scans can be performed on any part of the body.

PET scans use a radioactive tracer that is introduced into your body to measure the cellular activity of the cell type or body part being scanned. A CT scan takes a large number of x-rays. These are analyzed by a computer to create a 3-dimensional image of the body part being studied. When both tests are performed at the same time, the information about function and structure is integrated through computer models.

PET Scan of the Brain
PET scan head brain
Copyright © Nucleus Medical Media, Inc.

Reasons for Test

Because PET/CT scans provide a combination of information about the function and structure of a body part, they are useful for the early diagnosis of cancer. Not only can an abnormal tumor be seen, but the function of the cells that make up the tumor can be analyzed as well. This can help to differentiate between cancerous and noncancerous growths. PET/CT can also be used to see if cancer has spread into other areas of the body.

Brain, endocrine, and heart disorders are also studied using PET/CT scans.

Possible Complications

Some possible complications with this test include:

  • Allergic reactions to the chemicals used
  • Kidney damage from the contrast chemical used
  • Long-term effects from radiation exposure

What to Expect

Prior to Test

Prepare a list of medications you are taking and bring the list with you to the test. If you have diabetes, discuss taking your diabetic medications and/or insulin with your doctor prior to the test. An abnormal blood glucose level may interfere with the tests results.

Let your doctor know if you have kidney disease. The doctor may need to take steps to avoid kidney injury during the test.

To prepare for your test, you may need to do the following several hours in advance:

  • Not eat anything after a certain time
  • Avoid beverages with high sugar and calorie content
  • Drink plenty of water

If you are breastfeeding, talk to your doctor before you go for your test. Your doctor may recommend that you pump breast milk ahead of time and use it until the contrast materials are no longer in your body.

At the test center, the staff will ask if you have or ever have had:

Description of Test

  • If you are anxious about being in enclosed spaces, you may be given a light sedative to help you relax.
  • An IV will be placed in your arm.
  • A small quantity of the tracer substance (used for the PET portion of the scan) will be injected through the IV. In some cases, the tracer substance will be inhaled or swallowed rather than injected.
  • You will wait about 60 minutes after this injection.
  • You will be positioned on a table.
  • Another injection of contrast material (used for the CT portion of the scan) will be given.
  • The table will move slowly through a doughnut-shaped ring. You will need to lie still for about 35 minutes while the PET/CT images are being taken.

After Test

  • You should continue to drink extra water throughout the day after your scan. This helps to flush the tracer materials from your body.
  • If you have received any sedation, you will need to have someone drive you home.
  • You can expect to be able to resume your normal activities the same day as your test.

How Long Will It Take?

A PET/CT scan takes about a total of 2 hours to complete. The injection occurs about an hour prior to the start of the scan. The scan itself takes about 35 minutes.

Will It Hurt?

The placement of the IV may give you some discomfort, but there should be no other pain involved. You may feel some flushing when the tracer material is injected.


Based on the results, your doctor will decide if any further tests or treatments are needed.

Call Your Doctor

Call your doctor if any of the following occur:

  • Signs of allergic reaction, including flushing, hives, and itching
  • Swollen or itchy eyes
  • Difficulty breathing or a feeling of tightness in your throat
  • Nausea
  • Less urine than normal

If you think you have an emergency, call for emergency medical services right away.


Clinical Center—National Institutes of Health

Radiology Info—Radiological Society of North America

Canadian Resources

Canadian Cancer Society

Public Health Agency of Canada


PET/CT scan. Hartford Hospital website. Available at: Accessed February 16, 2016.

Positron emission tomography-computed tomography (PET/CT). Radiological Society of North America Radiology Info website. Available at: Updated June 11, 2013. Accessed February 16, 2016.

Schidt GP, Kramer H, et al. Whole-body magnetic resonance imaging and positron-emission tomography-computed tomography in oncology. Topics in Magn Res Imaging. 2007;18:193-202.