A radioactive form of glucose (sugar) often used during a positive emission tomography (PET) scan, a type of imaging test. In PET, a small amount of radioactive glucose is injected into a vein, and a scanner makes a picture of where the glucose is being used in the body. Cancer cells show up brighter in the picture because they are more active and take up more glucose than normal cells do. When used with PET, radioactive glucose helps find cancer cells in the body.