Gamma-ray imaging attempts to capture the distribution of radioactive decays within a body or from a distant source by detecting the emitted gamma rays. Unlike conventional x-ray or magnetic resonance imaging, gamma-ray imaging in humans and animals requires the introduction of a radioactive source into the body through injection, inhalation, or oral administration. The principal advantage of gamma-ray imaging over more conventional methods is that specially designed radiotracers can follow physiological pathways in the body. A number of chemicals are absorbed by specific organs. For example, the thyroid gland takes up iodine and the brain consumes glucose. With this knowledge, radiopharmacists are able to attach various radiotracers to biologically active substances such as iodine or glucose. In more conventional imaging such as transmission x-ray imaging, the anatomy of the patient is revealed, whereas gamma-ray imaging reveals the functional dynamics of processes in the body through so-called functional imaging.