A radioisotope, also known as a radionuclide or radioactive atom, is used to label radiopharmaceuticals for diagnosis. This radioisotope decays by emitting electromagnetic radiation, such as gamma- or roentgen (= X-) radiation (or positrons, as the annihilation of a positron with an electron generates two gamma rays of 511 keV almost immediately after the emission of the positron). The nature of gamma and roentgen radiation is similar to that of radio and television waves and light. A gamma camera or PET camera can be used to detect the gamma or X-rays that are released from the patient's body after the administration of a diagnostic radiopharmaceutical because electromagnetic radiation has a high penetrating power and is only minimally absorbed by tissues. PET stands for positron emission tomography. This data is transformed into scintigraphic images that display the spread of the radioactive material throughout the patient's body with the use of potent computer algorithms. The location and state of a specific disease, such as a tumour, metastasis, or infection, are visible on a scintigraphic image if the radiopharmaceutical is absorbed and used differently by pathological tissues or organs than by healthy tissues.