PET Scan
Reviewed
Also called: Positron Emission Tomography, category: imaging
A PET (positron emission tomography) scan is a nuclear imaging test that looks at how well your tissues and organs are working. It also checks for signs of cancer. For the scan, you will get an injection of a small amount of a tracer, which is a safe radioactive substance. The tracer settles in areas of your body that have high levels of chemical activity. This activity can be a sign of cancer or other diseases. The tracer can also help measure blood flow, oxygen use, and changes in the metabolism of a particular tissue or organ. Chemical changes in your body can show up before you even have symptoms of a disease. Since a PET scan can see how your organs are working in real-time, it can find signs of disease at an early stage, often before the disease can be seen on other imaging tests.
Specimen: No specimen required. The test involves intravenous injection of a radioactive tracer.
Why this test may be ordered
- To diagnose or monitor certain cancers, including breast, thyroid, and lung cancers
- To find out how well your heart muscle is working
- To check blood flow to your heart
- To check for signs of certain brain disorders, such as Parkinson's disease, Huntington's disease, Alzheimer's disease, and other types of dementia
Preparation and collection
Talk to your provider about how to prepare for the test. You may be asked to fast (not eat or drink) for four to six hours before the test. You may be asked to avoid tobacco products and food or drinks with caffeine or alcohol for 24 hours before the test. If you have diabetes and use insulin, you may need to change the timing of your regular dose. Your provider will give you specific instructions about adjusting your insulin since people with diabetes may not absorb the sugar in the tracer. This may affect the results of your scan. You may need to stop taking other medicines or supplements before the test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to. Also, tell your provider if you have claustrophobia (fear of enclosed spaces). Your provider may decide to give you a medicine to help you relax during the test.
No specimen collection required. The tracer is injected intravenously.
There is very little exposure to radiation in a PET scan. Only a small amount of radioactive substance is used, and it will leave your body through your urine and stool (poop) within 2 to 10 hours. Drink more water after the test to help remove the remaining tracer from your body. While radiation exposure in a PET scan is safe for most adults, it can be harmful to a developing baby. So be sure to tell your provider if you are pregnant or think you may be pregnant. Also, tell your provider if you are breastfeeding, since the tracer may contaminate your breast milk. Allergic reactions to the tracer are rare and usually mild.
Understanding results
Your PET scan results will be reviewed by a radiologist, a doctor who specializes in diagnosing and treating medical conditions using imaging technologies. They will share the results with your provider.
- No abnormal findings: The scan did not show any areas of unusually high or low chemical activity. This may indicate no signs of cancer, decreased blood flow to the heart, or brain chemical changes. Limitation: Some cancers don't show up on a PET scan, so your provider may order additional tests based on your symptoms and medical history. Next step: Routine
- Abnormal findings: The scan showed areas of abnormal activity, which may include: bright spots that can indicate cancer; decreased blood flow to the heart; or changes in brain chemicals associated with certain disorders. Limitation: Abnormal findings do not confirm a specific diagnosis; they are signs that need further evaluation. Some cancers may not show up on a PET scan. Next step: Routine
- Some cancers may not show up on a PET scan, so your provider may order additional tests based on your symptoms and medical history.
- The scan cannot diagnose a specific condition on its own; results are interpreted by a radiologist and correlated with other clinical information.
What to do next
Talk to your provider about your results. They will explain what the findings mean and whether any follow-up tests are needed.
- What should I do if I am pregnant or breastfeeding?
- How should I adjust my insulin if I have diabetes?
- What if I have claustrophobia?