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What is it? Overview Usage Side Effects and Warnings

PET/CT Scan Overview

Written by FoundHealth.


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. They are frequently used to gather information about the heart, brain, and lungs.

PET scans use a radioactive form of sugar (or other molecules) to measure the cellular activity of the body part being scanned. A CT scan takes a large number of x-rays. These are analyzed by a computer to create a three-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 of the Brain
© 2009 Nucleus Medical Media, Inc.

What to Expect

Prior to Test

  • Prepare a list of medicines you are taking; bring the list with you to the test.
  • If you have diabetes , discuss taking your diabetic medicines and/or insulin with your doctor prior to the test. An abnormal blood glucose level may interfere with the tests results.
  • If instructed to do so by your doctor:
  • Eat a high-protein, low-carbohydrate diet for the day or so prior to your test.
  • Drink about 3-4 glasses of water prior to arrival for your test.
  • Do not to eat for 6-8 hours prior to your test.
  • Inform the staff performing the test if you:
  • Ever had a reaction to a contrast agent or iodine in the past
  • Have asthma
  • Have a fear of small, enclosed spaces ( claustrophobia )

Description of Test

  • If you have a history of anxiety in small, enclosed spaces, you may be given a light sedative to help you relax.
  • An intravenous (IV) line 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 line.
  • You will wait about 45-60 minutes after this injection.
  • You will be positioned on a table.
  • Another injection of contrast agent (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 quite 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 agents 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 two hours to complete. The injection occurs about 45 minutes to an hour prior to the start of the scan. The scan itself takes about 35 minutes.

Will It Hurt?

The placement of the IV line will be slightly painful, but there should be no other pain involved. You may feel some flushing when the tracer agent is injected.


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



National Institutes of Health

Radiological Society of North America


BC Cancer Agency

Canadian Cancer Society


Adam A, Dixon A, Grainger R, Allison D. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. Philadelphia, PA: Saunders; 2008.

Grainger RG, Allison D, Adam A, Dixon AK, eds. Grainger & Allison’s Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. London, England: Elsevier; 2001.

Mettler FA. Essentials of Radiology. 2nd ed. Philadelphia, PA: Saunders; 2005.

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



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