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PET/CT scan is a type of imaging test that combines positron emission tomography (PET) and computed tomography (CT) techniques.

PET scans use a radioactive form of glucose (or other molecules) to measure the cellular functioning of the body part being scanned. A CT scan takes a large number of x-rays that are analyzed and assembled 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 are integrated through computer models.

PET Scan of the Brain

PET scan head brain

© 2008 Nucleus Medical Art, Inc.

Parts of the Body Involved

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.

Reasons for Procedure

Because combined PET/CT scans provide a unique combination of both functional and structural information, they are particularly useful for the early diagnosis of cancer. Not only can the presence of an abnormal tumor be noted, but the function of the cells that make up the tumor can be analyzed, helping to differentiate between benign and malignant growths. PET/CT is also used in re-staging previously diagnosed cancer.

Each of these tests has its own limitations, but when combined, they provide very precise information on cancer location and metabolism. In the past, both of the tests had to be done separately, which made the interpretation of results more difficult due to the fact that the patient’s body position changed. However, with the availability of new scanners that combine both technologies this is no longer a problem. Many cancer specialists believe that this technology will allow doctors to reduce the number of invasive procedures that patients need to undergo (eg, biopsies ) and still be able to provide very accurate monitoring.

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

Risk Factors for Complications During the Procedure

What to Expect

Prior to Procedure

  • Prepare a list of medications you are taking; 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 taking 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 the 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 )


No anesthesia is used. In some instances, if you have a history of anxiety in small, enclosed spaces (claustrophobia), you may be given a light sedative to help you relax.

Description of the Procedure

  • 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 for the actual scan.
  • Another injection of enhancing 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 Procedure

  • You will not have any restrictions of activity or diet after this procedure.
  • You should continue to drink extra water throughout the day after your scan, to flush the tracer agents from your body.
  • If you have received any sedation, you will need to have someone drive you home.

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 actual 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.

Possible Complications

  • You may notice warmth and flushing when the tracer is injected. This feeling is normal.
  • If you are allergic to either of the substances injected, you could have an allergic reaction. This can be treated with antihistamines and/or steroid medications.
  • Rarely, an individual with already-existing kidney disease may experience further kidney damage.
  • People who are prone to claustrophobia may have an anxiety attack during the course of the PET/CT scan.

Average Hospital Stay

This test does not require a hospital stay.

Postoperative Care

No special care is necessary.


You can expect to be able to resume your normal activities the same day as your test. If you have received sedation during the course of the exam, you will need someone to drive you home from the exam.

Call Your Doctor If Any of the Following Occurs

  • Rash, hives , itching
  • Flushing or redness after the test
  • Wheezing or shortness of breath
  • Decreased urine output


Radiological Society of North America

National Institutes of Health


BC Cancer Agency

Canadian Cancer Society


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

Last reviewed April 2008 by Rimas Lukas, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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