PET Scan

Author: Courtney Misher, MPH, BS R.T.(T)
Last Reviewed: August 23, 2022

A PET (positron emission tomography) scan is an imaging test. It uses radioactive materials, called tracers, to see how well your tissues and organs are working.

Why is a PET scan done?

PET scans are used to find heart problems, brain disorders, and cancer. If a PET scan is being used for cancer, then it may be used to:

  • Find and diagnose cancer.
  • Check if your cancer has spread to other areas of your body.
  • See how your body is responding to treatment.
  • Check if your cancer has returned after treatment.

How does a PET scan work?

A radioactive tracer is given through a vein in your arm (IV), a drink, or a gas you breathe in. The tracer is often attached to glucose (a sugar molecule). The tracer and glucose combination is called fluorodeoxyglucose (FDG).

After it enters your body, it goes to areas that have higher levels of chemical activity (areas where there is cancer or another disease). Tumor cells have a high rate of activity. This causes the tumors to take up, or attract, more of the tracer. These areas will look more "active" or brighter than other areas on the PET scan.

Often, a CT scan is done at the same time. A PET/CT scan makes a 3-dimensional (3D) image using the x-ray images from CT and fusing them with images of the affected tissue from the PET. A PET/CT test helps diagnose cancer and gives more information, including:

  • Treatment planning scans.
  • Whether a tumor is benign (non-cancerous) or malignant (cancerous).
  • If the cancer cells are active or not.
  • How well the cancer is responding to treatment.

How do I prepare for a PET Scan?

Your care team will tell you how to prepare for your PET scan, but you may be asked to:

  • Wear comfortable clothing that is easy to take on and off. You will likely need to wear a gown for the test and remove all jewelry in the scan area.
  • 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).
  • Stop taking certain medications for diabetes, as they could affect the tracer.
  • Not eat anything for some time before the test.
  • Avoid exercise and caffeine the day before and the day of the scan.
  • 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.

If you are pregnant, think you could be pregnant, or are breastfeeding you should tell your provider before getting a PET scan.

How is a PET scan done?

A PET scan is usually done as an outpatient procedure (you do not need to stay overnight) and takes 2-3 hours. You will be given the tracer. The test will not start for about 60-90 minutes so that the tracer 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 be given medication to help you relax. How long the test takes depends on how much of your body is being scanned. The technician can hear and see you during the test if you need to talk with them.

What should I expect after the PET scan?

If you received medication to help you relax, 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 tracer. You should drink plenty of water to clear the tracer from your body. Ask your provider if you need to limit your contact with pregnant women or infants for any amount of time after the test.

How do I get the results of my PET scan?

It is possible for noncancerous conditions to look like cancer and for some cancers not to show up on PET scans. For this reason, it is important for a specialist to carefully review the test results. They will send a report to your provider. Your provider will go over the results with you. Be sure to ask your provider if you have any questions.


U.S. National Library of Medicine. (2020, July 3). Pet scan: Medlineplus medical encyclopedia. MedlinePlus. Retrieved August 22, 2022, from

Radiological Society of North America (RSNA) and American College of Radiology (ACR). (2021, February 8). PET/CT. Retrieved August 22, 2022, from


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