Nuclear medicine involves using radioisotopes (radioactive chemicals) in the diagnosis, management and treatment of disease. Radioactive substances emit energy waves due to decaying atomic nuclei. They act as tracers for diagnosis, and in treatment to kill cancerous cells. Usually, small amounts of radioactive materials or radiopharmaceuticals are used, substances that are attracted to specific organs, bones or tissues. The radiopharmaceuticals emit gamma rays that can be detected externally by gamma or PET cameras. Images are then assembled by computers to provide data and information about the area of body being imaged. Treatment with nuclear medicine is based on the destructive power of radiation, which is used to remove unwanted, especially cancerous, tissues. The radiation used travels only a short distance, thereby minimising unwanted side-effects and damage to non-involved organs or nearby structures.