PET scan

Originally Published: March 1, 1996 - Last Updated / Reviewed On: November 23, 2012
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Dear Alice,

Can you tell me what a PET scan is?

Dear Reader,

Positron emission tomography (PET) is an imaging technique used by radiologists to observe biological processes in the human body. PET scans can be used to help doctors diagnose a variety of ailments including heart and brain problems or even to determine the location and size of cancerous lesions. In order to provide doctors a better picture of what is going on inside the body, PET scans are often combined with computed tomography (CT) scans which show the 3-D structure of the inside of the body. Together, this combined scan is called a PET/CT scan.

PET scans work by detecting the emission of positrons (positively charged electrons) inside a person’s body. In order for the scanner to do this, patients are given a substance called a tracer. When a patient is scheduled to get a PET scan, s/he will be asked not to eat or drink anything except water for four to six hours before the scan. This is to make sure that the tracer is actually absorbed throughout the body. About one hour before the scan begins, the patient will be given a small amount of tracer intravenously. During that hour the tracer will travel in the blood throughout the body so it can be absorbed. The patient will be asked to lie on a metal table that slowly moves into a large machine that is able to scan the body. The patient is asked to lie as still as possible so that the images will come out clearly. If a person is claustrophobic (has a fear of small spaces) or is unable to lie still for the entire time scanning process, s/he should let the health care provider know.

PET scans are considered low-risk. However, if a person is pregnant or breast-feeding, she should let her healthcare provider know since infants and unborn babies are more vulnerable to the effects of radiation than others. Some people are allergic to the radioactive tracer and might have redness, swelling, or pain at the injection site.

Overall, a PET scan is a powerful diagnostic tool that is expected to play an even greater role in diagnostic medicine as the technology continues to advance.

Alice