by Rosalyn Carson-DeWitt, MD
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 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.
Reasons for Test TOP
Because combined PET/CT scans provide a combination of information about the function and structure of a body part, they are very 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 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.
Each of these tests has its own limitations. When combined, they provide very precise information on cancer location and activity. In the past, both of the tests had to be done separately, making the interpretation of results more difficult due to changes in the patient’s body position. However, with the availability of 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 and still be able to provide very accurate monitoring.
Brain, endocrine, and heart disorders are also studied using PET/CT scans.
Possible Complications TOP
Some possible complications with this test include:
What to Expect TOP
Prior to Test
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 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:
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 talk to the staff if you have or ever have had:
Description of Test
After Test TOP
How Long Will It Take? TOP
A PET/CT scan takes about a total of two hours to complete. The injection occurs about 60 minutes to an hour prior to the start of the scan. The scan itself takes about 35 minutes.
Will It Hurt? TOP
The placement of the IV line 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 TOP
Call your doctor if any of the following occurs:
If you think you have an emergency, call for medical help right away.
National Institutes of Health
Radiological Society of North America
Canadian Cancer Society
Public Health Agency of Canada
PET/CT scan. Hartford Hospital website. Available at:
...(Click grey area to select URL)
Accessed May 22, 2013.
Positron emission tomography-computed tomography (PET/CT). Radiological Society of North America Radiology Info website. Available at:
...(Click grey area to select URL)
Updated March 28, 2013. Accessed May 22, 2013.
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.
Last reviewed February 2014 by Michael Woods, MD
Last Updated: 3/18/2013