What is a positron emission tomography scan?

A positron emission tomography (PET) scan is a unique type of imaging test that helps doctors see how the organs and tissues inside your body are actually functioning.

The test involves injecting a very small dose of a radioactive chemical, called a radiotracer, into the vein of your arm. The tracer travels through the body and is absorbed by the organs and tissues being studied.

Next, you will be asked to lie down on a flat examination table that is moved into the center of a PET scanner—a doughnut-like shaped machine. This machine detects and records the energy given off by the tracer substance and, with the aid of a computer, this energy is converted into three-dimensional pictures. A physician can then look at cross-sectional images of the body organ from any angle in order to detect any functional problems.

What problems can a PET scan detect?

A PET scan can measure such vital functions as blood flow, oxygen use, and glucose metabolism, which helps doctors identify abnormal from normal functioning organs and tissues. The scan can also be used to evaluate the effectiveness of a patient's treatment plan, allowing the course of care to be adjusted if necessary.

Currently, PET scans are most commonly used to detect cancer, heart problems (such as coronary artery disease and damage to the heart following a heart attack), brain disorders (including brain tumors, memory disorders, seizures) and other central nervous system disorders.

How is a PET scan different from a CT or MRI scan?

One of the main differences between PET scans and other imaging tests like computed tomography (CT) scan or magnetic resonance imaging (MRI) is that the PET scan reveals the cellular level metabolic changes occurring in an organ or tissue. This is important and unique because disease processes often begin with functional changes at the cellular level. A PET scan can often detect these very early changes whereas a CT or MRI detect changes a little later, as the disease begins to cause changes in the structure of organs or tissues.