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.
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. If you have diabetes and use insulin, you may need to change the timing of your regular dose. 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.
A health care provider will inject the radioactive tracer into your vein through an intravenous (IV) line. You will need to wait for your body to absorb the tracer, which takes 45 to 60 minutes. As this happens, you will need to be very still for about 30 minutes. The test takes about two hours to complete, including the time you wait for the tracer to be absorbed by your body.
There is very little exposure to radiation in a PET scan. 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
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.
- Bright spots (possible cancer): Cancer cells show up as bright spots on a PET scan. 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: If you have questions about your results, talk to your provider.
- Decreased blood flow to the heart: The scan can show decreased blood flow to the heart. Limitation: Your PET scan results will be looked at by a radiologist, a doctor who specializes in diagnosing and treating medical conditions using imaging technologies. Next step: If you have questions about your results, talk to your provider.
- Changes in brain chemicals: The scan may show changes in certain brain chemicals that can be a sign of a disease. Limitation: Your PET scan results will be looked at by a radiologist, a doctor who specializes in diagnosing and treating medical conditions using imaging technologies. Next step: If you have questions about your results, talk to your provider.
- 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
If you also had a CT scan, your provider will review the results of the two scans to help make a diagnosis. If you have questions about your results, talk to your provider.
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Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.