PET Scan

OncoLink Team
Last Modified: June 11, 2018

What is a PET scan?

PET stands for Positron Emission Tomography. It is a medical test that uses a radioactive substance, also known as a tracer. The tracer can be injected, 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). 

Tumor cells have a high rate of metabolism (chemical activity) and because of this, they take up more of the tracer. When PET is used in cancer patients, the tracer is typically attached to glucose (a sugar molecule). This combination is called FDG (fluorodeoxyglucose). Tumor cells take up glucose. This makes the cancer cells appear more "active" than other areas on the scan pictures. It is important to remember that a PET scan is not able to differentiate between activity due to tumor and activity due to non-cancerous processes, such as inflammation or infection. 

Often, a PET scan is combined 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 to diagnose cancer and provide additional 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?

You will be given detailed instructions but in general:

  • Bring a list of the medications that you are taking, brief medical history, and treatments that you have had (chemotherapy, radiation therapy, or surgery). 
  • If you take any medications for diabetes, you may be instructed not to take these, as they could interfere with the FDG tracer. 
  • You will be given instructions as to how long you need to fast (not eat) prior to the test. 
  • You should avoid vigorous physical exercise the day before, on the day of the scan, and until the scan is completed.

How is this test performed?

The test will take 2-3 hours, from start to finish. You will be given the radioisotope (FDG) in an intravenous (IV), injection or inhaled as a gas. The test will not start for about 60-90 minutes so that the FDG can circulate (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. The amount of time the test takes depends on how much of the body is being imaged. 

What to expect after the PET scan?

If you received sedation you will need someone to drive you home. You can resume your normal diet and activity. 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 receive 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 review the results with you. 

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