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Introduction
Procedure
Technical Details
Risks
Positron emission tomography (PET) is a form of nuclear medicine imaging which uses very small amounts of radioactive material to diagnose certain abnormalities within the body by looking at the metabolic picture of the tissue under study. This is a noninvasive and usually painless medical test that can help physicians diagnose certain conditions whithin the brain which may not be as easily discernable on other types of brain imaging such as magnetic resonance imaging (MRI) or computer tomography (CT). In some cases, PET images can be superimposed with computed tomography (CT) or magnetic resonance imaging (MRI) to produce special views, a practice known as image fusion or co-registration. These views allow the information from two different studies to be correlated and interpreted on one image, leading to more precise information and accurate diagnoses. A brain PET image is depicted below.
After injection of the radioactive material (radiotracer) through an intravenous line, the patient will wait from 30 to 60 minutes for the substance to travel through the body and accumulate in the appropriate tissues. The imaging process will then start, which will typically takes place on a PET scanner similar to the one depicted below.
Once the area of the body to be imaged has been properly positioned, images through the area of interest are obtained. The entire image acquisition can take up to one hour. While lengthy, the PET scan is typically not an uncomfortable process. In many cases, the entire examination will be performed by a PET technician who is not a doctor. However, the supervising radiologist should be available to consult as necessary during the exam, and will view and interpret the results.
During a brain PET scan, a radioactive substance (typically a form of sugar) is injected into a vein and allowed to circulate within the body. This substance, called a radiotracer, eventually collects in the tissues being examined to varying degrees. Typically, regions that have high metabolism (such as tumors) will accumulate more radiotracer whereas areas that are normal will accumulate relatively less. The accumulated radiotracer gives off rays of energy which are detected by the PET scanner. These devices work together with a computer to measure the amount of radiotracer absorbed by the body and to produce special pictures offering details on both the structure and function of the brain and other internal body parts.
PET scanning utilizes radioactive tracers which while relatively harmless at low doses, can potentially increase the risk of certain types of cancers in chronic or repeated exposure. Furthermore, exposure to to thes agents during pregnancy can increase the risk of birth defects. Therefore, all individuals, especially woman who are, or may be, pregnant, should carefully discuss this issue with their physician and radiologist before undergoing a scan in order to weigh the benefits of the PET scan against its potential risks.
