Positron Emission Tomography (PET) Health Article

Definition

Positron emission tomography (PET) is a non-invasive scanning technique that utilizes small amounts of radioactive positrons (positively charged particles) to visualize body function and metabolism.

Purpose

As of 2001, PET is the fastest growing nuclear medicine tool in terms of increasing acceptance and applications. It is useful in the diagnosis, staging, and treatment of cancer because it provides information that cannot be obtained by other techniques like computed tomography (CT) and magnetic resonance imaging (MRI).

PET scans can be performed at medical centers equipped with a small cyclotron. Smaller cyclotrons and increasing availability of certain radiopharmaceuticals are making PET a more widely used imaging modality.

Physicians first used PET to obtain information about brain function and to study brain activity in various neurological diseases and disorders, including stroke, epilepsy, Alzheimer's disease, Parkinson's disease, and Huntington's disease; and in such psychiatric disorders as schizophrenia, depression, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, and Tourette syndrome. More and more, PET is being used to evaluate patients for head and neck, lymphoma, melanoma, lung, colorectal, and esophageal cancers. PET also is used to evaluate heart muscle function in patients with coronary artery disease or cardiomyopathy.

Precautions

There is always a slight risk when radioactive material is injected into the body. However, because the radioactive tracers used are short-lived and clear the body quickly, they are considered safe. The radiation dose received is only slightly more than that received in a chest x ray. Still, pregnant women should not have a PET scan.

Description

PET involves injecting a patient with a radiopharmaceutical similar to glucose. An hour after injection of this tracer, a PET scanner images a specific metabolic function by measuring the concentration and distribution of the tracer throughout the body.

When it enters the body, the tracer courses through the bloodstream to the target organ, where it emits positrons. The positively charged positrons collide with negatively charged electrons and gamma rays are produced. The gamma rays are detected by photomultiplier scintillator combinations positioned on opposite sides of the patient. These signals are then processed by the computer and images are generated.

PET provides an advantage over CT and MRI because it can determine if a lesion is malignant. The two other modalities provide images of anatomical structures but often cannot provide a determination of malignancy. Recently, PET has been used in combination with CT and MRI to identify abnormalities with more precision and indicate areas of most active metabolism. This additional information allows for more accurate evaluation of cancer treatment and management.