PET scan


Positron Emission Tomography, also known as a PET scan, is called a functional study because it creates pictures based on the activity of specific cells. It is used to detect cancer throughout the body.

PET scans are not a routine test after a diagnosis of breast cancer, but sometimes doctors order them to see if the cancer has traveled outside the breast to the lymph nodes or elsewhere such as the bones, liver, lungs or brain. PET scans are also useful to see whether treatment for metastatic breast cancer is working.

A PET scan is often performed along with a CT scan, called a PET-CT, to more precisely locate the area of abnormal activity.

Getting the test

Before the test, a technologist will inject a substance made up of sugar molecules labeled with radioactive material. This material will be drawn to cells with high levels of metabolic activity, such as cancer cells. On the PET scan, areas of high activity show up brighter than other areas. After the scan, your doctor may order more tests to get detailed information about any suspicious areas.

Your doctor may ask you not to eat for several hours before the test. If you have diabetes or other illnesses, you’ll receive special instructions to ensure the test gives accurate results. You must remove metal jewelry and other objects before the test, and you should let your doctor know if you have any metal inside of your body because it could affect how the scan sees the images. You may be asked to change into a hospital gown.

A PET scan machine looks somewhat like a CAT or CT scan machine or an MRI (Magnetic Resonance Imaging) machine. After the injection, you will lie down or sit quietly for about an hour while your body absorbs the sugar-radioactive mixture. Then, you will lie on a narrow table that will move through a hole in the center of a round scanner. This scanner will take pictures of your body.

During the test, which lasts about 30 minutes, you must lie very still. Except for the needle prick from the injection, you should not feel pain during the test.


Reviewed and updated: August 31, 2015

Reviewed by: Marion Brody, MD


Was this page helpful?