Positron emission tomography, also called PET imaging or PET scan, is a test that images the function of cells to show differences between healthy tissue and diseased tissue. It uses a small amount of a radioactive chemical which is combined with sugar. This combination is called F-18 fluorodeoxyglucose or FDG, so the test is sometimes called an FDG-PET scan. It is used to evaluate various neurological and cardiac disorders, as well as for diagnosing, staging and monitoring the treatment of many different cancers. To perform the PET scan, a small amount of FDG is injected into the patient. Because cancer grows at a faster rate than healthy tissue, cancer cells take up more of the FDG. The PET scanner detects the radiation given off by the FDG and produces color-coded images of the body that show both normal and cancerous tissue. Most current PET scanners also include a conventional x-ray computed tomography (CT) scanner. This allows images of both anatomy (CT) and function (PET) to be taken during the same examination.

FDG is a glucose molecule which has been tagged with a small amount of radioactive element. This product is injected into the body during a PET scan. The radioactive glucose is taken up by the cancer cells and then these cancer cells can be identified. This glucose molecule only stays in the body for about 2 hrs and is then excreted. The amount of glucose injected is miniscule and has no affect on diabetic patients.