The amount of the radiopharmaceutical given to a patient for diagnostic purposes is just sufficient to obtain the required information before its decay. The radiation dose received is considered medically insignificant. The patient experiences no discomfort during the test and after a short time there is no trace that the test was ever done. The non-invasive nature of this technology, together with the ability to observe an organ functioning from outside the body, makes this technique a powerful diagnostic tool .A radioisotope used for diagnosis must emit gamma rays of sufficient energy to escape from the body and have a half-life short enough for it to decay completely soon after imaging is completed. The radioisotope most widely used in medicine is technetium-99m, employed in some 80% of all nuclear medical procedures. It is an isotope of the artificially-produced element technetium and has almost ideal characteristics for a nuclear medical scan. • Its half-life of six hours is long enough to image or examine a metabolic process yet short enough to minimize the radiation dose to the patient .<br /> • Technetium-99m decays by a process called isomeric decay which emits gamma rays and low energy electrons. Since there is no high energy beta emission the radiation dose to the patient is low .<br /> • The low energy gamma rays it emits easily escape the human body and are accurately detected by a gamma camera. Once again the radiation dose to the patient is minimized .<br /> • The chemistry of technetium is versatile. It can form tracers by being incorporated into a range of biologically-active substances to ensure that it concentrates in the tissue or organ of interest. Technetium generators, comprising a lead pot enclosing a glass tube containing the radioisotope, are supplied to hospitals from the nuclear reactor where the isotopes are made. They contain molybdenum-99, with a half-life of 66 hours, which progressively decays to technetium-99m. The Tc-99m is washed out of the lead pot by saline solution when it is required. After approximately two weeks the generator is returned for recharging.<br />