How are nuclear medicine imaging tests generally performed?
A radiotracer is administered to a patient (most commonly intravenously, although oral or inhalational routes are also possible). After waiting for a certain delay time to allow for biodistribution of the radiotracer, the patient is then placed into the scanner. For planar scintigraphy and SPECT, gamma rays are emitted by the radioactive isotopes in the radiotracers. For PET, positrons that are emitted by the radioactive isotopes in the radiotracer molecules travel several millimeters within tissue before annihilating with electrons that are encountered, leading to emission of two gamma rays in opposite directions. The gamma rays leave the body, pass through a collimator (in planar scintigraphy and SPECT), and are detected by one or more scintillation crystals in detectors surrounding the patient. The light signals created by the scintillation crystals are then detected by photomultiplier tubes (PMT), which lead to creation of voltage signals that are digitized for computers to process. Ultimately, when enough signals are detected, the computer reconstructs images that reflect the spatial distribution and amount of accumulation of the radiotracer in organs/tissues of the body (which depend on the properties of the administered radiotracer and the disease states present in the patient).