PET Scan

Author: OncoLink Team
Last Reviewed: April 30, 2020

What is a PET scan?

A PET scan is an imaging test. Your provider might order a PET scan to see how tissues and organs in your body are working and to check for any disease or inflammation. PET stands for Positron Emission Tomography. It uses a radioactive substance, called a tracer. The tracer can be injected into a vein, swallowed, or inhaled (as a gas) into the body. After it enters your body, it goes to areas that have higher levels of chemical activity (such as areas where there is cancer or other disease). These areas of activity will show up as bright spots on the PET scan for your provider to see. 

Tumor cells have a high rate of metabolism (chemical activity). These active tumors take up, or attract, more of the tracer. When PET is used in cancer patients, the tracer is often attached to glucose (a sugar molecule). The tracer and glucose combination is called FDG (fluorodeoxyglucose). Tumor cells take up glucose. This makes the cancer cells look more "active" or brighter than other areas on the scan pictures. It is important to remember that a PET scan can show many things. The scans can’t tell the difference between activity due to a tumor and activity due to non-cancerous processes, such as inflammation or infection. 

Often, a PET scan is done with a CT scan in one test. The machine merges the images from the PET and CT together to determine functional (PET) and structural information (CT). A PET/CT test helps diagnose cancer and gives more information, including whether a tumor is benign (non-cancerous) or malignant (cancerous), whether the cancer cells are active or dead, and how well the cancer is responding to treatment. 

How do I prepare for a PET Scan?

Your care team will talk with you about how to get ready for your PET scan, but in general:

  • Bring a list of the medications that you are taking, a brief medical history, and treatments that you have had (chemotherapy, radiation therapy, or surgery). 
  • If you take any medications for diabetes, you may be told not to take these, as they could affect the FDG tracer. 
  • You will be told how long you need to fast (not eat) prior to the test. 
  • You should avoid physical exercise the day before, on the day of the scan, and until the scan is over.
  • You will need to lie still during the test, which could be 30-60 minutes long. Talk with your provider if you think you might have a hard time doing so. 

How is a PET scan done?

The test will take 2-3 hours, from start to finish. You will be given the FDG in an intravenous (IV, in a vein) injection or inhaled as a gas. The test will not start for about 60-90 minutes so that the FDG can move around your body. After this time, you will lie on a table that can slide into the scanner. The scanner is a donut-shaped machine. The scan takes 30-60 minutes and you will need to lie still. You may receive a medication to help you relax, called sedation.  How long the test takes depends on how much of the body is being scanned. You will be able to talk with the technician during the test.

What should I expect after the PET scan?

If you received sedation to help relax you, you will need someone to drive you home. You can go back to your normal diet and activity the next day. People do not often have any side effects from the FDG. You should drink plenty of water to clear the FDG from your body. 

How do I get the results of my PET scan?

A specialist will review the results of your PET scan and send a report to your provider. Your provider will go over the results with you.

If your provider has ordered a PET scan for you, be sure to ask any questions you may have. Talk with your team about why the scan was ordered, how you should prepare, what to expect the day of, and how and when you will get your results. 

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