What is a PET scan?

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

In a PET scan, a very small dose of a radioactive chemical, called a radiotracer, is injected into the vein of your arm. The tracer travels through the body and is absorbed by the organs and tissues that are being studied.

Then, 45 minutes after the injection, you will lie down on a flat examination table that is moved into the center of a PET scanner, a doughnut-shaped machine. This machine detects and records the energy given off by the tracer substance. 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 organ from any angle in order to detect any problems.

What can a PET scan detect?

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

A PET scan can:

  • Measure vital functions such as blood flow, oxygen use, and glucose (blood sugar) metabolism to help doctors identify organs and tissues that are not working properly.
  • Detect tumor cells for initial cancer staging (classification).
  • Evaluate how well a patient's treatment plan is working, allowing the care to be adjusted, if necessary.

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

One of the main differences between PET scans and imaging tests like a computed tomography (CT) scan or magnetic resonance imaging (MRI) is that the PET scan reveals metabolic changes in an organ or tissue earlier--at the cellular level. This is important and unique because diseases often begin with functional changes in the cells. 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.

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