PET or Positron Emission Tomography is a branch of nuclear medicine. PET imaging uses FDG, a radioactive sugar, to create images. Cancer cells absorb sugar more quickly than normal cells, so they "light up" on the images created by the PET scanner. CT or CAT scan uses x-rays and a computer to make an image of sections of your body. CT shows internal anatomy that reveals the location, size and shape of abnormal cancerous growths. Alone, each imaging test has particular benefits and limitations but when the results of PET and CT scans are "fused" together, the combined image provides more accurate information on cancer detection, staging of cancer, checking for tumor recurrence and treatment response. As a result, PET/CT scans can minimize and often help patients avoid unnecessary invasive tests, including surgery.