A positron emission tomography (PET) scan is a type of nuclear medicine imaging test. It is used to examine various body tissues to identify certain conditions by looking at blood flow, metabolism, and oxygen use. PET scans may also be used to see how well the treatment of certain diseases is working.
For a PET scan, a tiny amount of a radioactive substance, called a radioactive tracer is used to show the metabolism of a particular organ or tissue. This test gives the healthcare provider information about the function and structure of the organ or tissue. It also gives information about its biochemical properties. A PET scan may detect biochemical changes in an organ or tissue that are signs of a disease process before physical changes related to the disease can be seen with other imaging tests. These include computed tomography (CT) or magnetic resonance imaging (MRI).
PET scans are often done along with CT scans (called a PET/CT scan) to give more definitive information about metabolism changes and exactly where they are happening in the body.
PET works by using a special camera that detects positrons emitted by the radioactive tracer in the organ or tissue being examined.
The radioactive tracers are attached to a chemical substance that a particular organ or tissue uses during metabolism. These substances include glucose, carbon, or oxygen. For example, in PET scans of the brain, a radioactive substance is applied to glucose to create a radionuclide called fluorodeoxyglucose (FDG), because glucose is widely used for metabolism. FDG is widely used in PET scanning.
Other substances may be used for PET scanning, depending on the purpose of the scan. If blood flow and perfusion of an organ or tissue is of interest, the radionuclide may be a type of radioactive oxygen, carbon, nitrogen, or gallium.
The radioactive tracer/sugar is put into a vein through an intravenous (IV) line. It moves through the blood and collects in areas with a lot of cell activity. During this time, the PET scanner slowly moves over the body. A computer creates a map of the body. The amount of the radionuclide collected in the tissue affects how brightly the tissue appears on the image. It also indicates the level of sugar uptake or cell activity in that organ or tissue.
For example, cancer cells use a lot of sugar and will show up as bright spots (called “hot spots”) on a PET scan. Damaged heart tissue will be less active and use less sugar. It would be seen as a darker spot compared to the normal heart tissue.
In general, PET scans are used to evaluate organs and/or tissues for the presence of disease or other conditions. More specific reasons for PET scans include:
There may be other reasons for your healthcare provider to recommend a PET scan.
The amount of the radionuclide injected into your vein for the procedure is very small, and there is no need for precautions against radiation exposure. The injection of the radionuclide may cause some slight discomfort. Allergic reactions to the radionuclide are rare, but may happen. Tell your healthcare provider if you are allergic to or sensitive to medicines, contrast dyes, iodine, or latex.
For some people, having to lie still on the scanning table for the length of the procedure may cause some discomfort or pain.
Tell your healthcare provider if you are pregnant, or think you may be pregnant or breastfeeding.
There may be other risks depending on your specific medical condition. Be certain your healthcare provider knows about all of your medical conditions.
Certain factors or conditions may interfere with the accuracy of a PET scan including:
Tell your healthcare provider if any of the above situations may apply to you.
PET scans may be done on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare provider's practices.
Generally, a PET scan follows this process:
While the PET scan itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly if you have recently had surgery or a joint injury. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.
Be sure to move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness.
You will be instructed to drink plenty of fluids and empty your bladder often for 24 to 48 hours after the test. This will help flush the remaining radioactive tracer from your body.
The IV will be removed and the site will be checked for any signs of redness or swelling. Tell your healthcare provider if you notice any pain, redness, and/or swelling at the IV site after you go home. This may be a sign of infection or other type of reaction.
Your healthcare provider may give you additional or alternate instructions after the procedure, depending on your particular situation.
Before you agree to the test or the procedure make sure you know:
Stroke is a leading cause of death and a
leading cause of serious, long-term disability, according to the American Heart Association (AHA) and the American Stroke Association (ASA). The ASA reports that strokes are the fourth leading cause of death in the U.S. Find out more about stroke by taking this quiz, based on information from the AHA and the National Institute of Neurological Disorders and Stroke (NINDS).