The positron emission tomography scan is a biological scan coupled with anatomical CT scan. It exploits the high metabolic rate of cancer cells. Because of this high metabolic rate, cancer cells usually have a very high demand for glucose. This principle is utilized in PET scan. A radioactive material is usually tagged with a glucose analogue which after entering the body gets selectively trapped inside the tumor cells more than normal cells. The radioactive material emits radiation which is detected by the scanner and the tumor brightens up beautifully during the scan. Most commonly, the radioactive tracer and metabolite include 18F-Fluoro Deoxyglucose (FDG). When PET scan is combined with CT scan it becomes more useful as CT scan provides anatomical details at the region of abnormality. Both these scans are done at one go in the same machine at the same time.