The unique power of a PET scan lies in its ability to "see" the chemical activity inside the body. In order to do this, a chemical tracer is added into the bloodstream that the PET scanner is able to pick up. In many cases, a glucose (sugar) tracer containing the chemical FDG is used.

Shortly after the tracer enters the blood stream, organs and tissue begin to break down the glucose which is used for energy. In doing so, a proportional amount of FDG remains which can be seen by the PET scanner.

The PET scanner is able to then capture an image of the FDG concentration, providing a detailed series of image slices, or tomography, of the glucose metabolism. These images can then be studied to reveal any highly active metabolic tissue inside the body which is consistent in disease like cancer, diabetes, neurological disorders and tumors.

In the same way, aggressive, fast growing tumors and cancer will also have an increased rate of metabolism compared to other tissue in the body. The presence of these active diseases are readily noticeable on the PET image.

In some cases, tumors or other abnormalities in the body can be very similar in density to normal tissue and may not even appear in a CAT scan or MRI. But with a PET scan, these abnormalities are easily detected because of PET's ability to see the tissue's chemical makeup and varying metabolism

For an even more comprehensive view, these individual tomographic slices can then be fused together into a Maximum Image Projection, or "MIP". The resulting image is a three-dimensional view of the body and its chemical function.

By nature, the kidneys, bladder, heart and brain utilize glucose at a high rate and therefore will usually show up as "hot spots" on an FDG PET scan. Any other highly metabolic tissue like cancer or active tumors will also be revealed and can then be treated.

The information provided through PET imaging is not only valuable in the diagnosis of disease, but also in the monitoring of treatment. During the treatment of a disease, subsequent scans can be taken and compared against one another. And while other imaging techniques may still show the existence of the diseased mass, only PET images have the ability to show its current level of activity. Physicians use this information to monitor the effectiveness of a treatment and in monitoring its success.