Radiopharmaceuticals Nuclear cardiology is based on the administration of a radiopharmaceutical consisting of a radionuclide (isotope) with or without a complexing agent (depending on the type of study) in order to image the cardiovascular system. A radionuclide is an unstable element that decays spontaneously and, as a result, emits energy in the form of radiation or charged particles.Radiation that is emitted from the decay of the nucleus of an atom is called gamma radiation. With some isotopes, the radiation is reabsorbed by the orbiting electrons and then re-emitted as x-rays.Gamma rays are high-energy electromagnetic radiation. By comparison, light is considered low-energy electromagnetic radiation.The energy of a gamma ray is described in units of electron volts, typically between 50,000 and 200,000 electron volts (abbreviated as 50200 keV). Radiopharmaceuticals also may consist of a complexing agent (sestamibi or tetrofosmin) that helps
to facilitate stabilization, biodistribution, and delivery of the radionuclide to the intended target. If the emitted gamma rays from the administered radionuclide are not absorbed or scattered by soft tissue or bone and pass out of the body, they can be detected and used to create an image.