Radiopharmaceuticals

Radiopharmaceuticals are radioactive pharmaceuticals used in medical imaging as tracers for the identification and diagnosis of many illnesses. Nuclear medicine modalities – SPECT and PET – use radiopharmaceuticals to generate diagnostic images. These nuclear pharmaceuticals combine physiologically active carriers with a radioisotope. It is possible to manufacture chemical or biological carriers which migrate to a particular part of the human body.

For example, iodine concentrates in the thyroid gland. The radioisotope attached to these compounds emits radiation so that the relevant organ and its functioning can be imaged.

A radiopharmaceutical, which involves the use of radioactive agents in vivo to diagnose or treat specific diseases and conditions, generally consists of two components which determine its characteristics and clinical potential. The most common diagnostic molecular imaging agents use radioactive isotopes as the signal source. A radioactive isotope -- a radioisotope or radionuclide -- is a natural or artificially created isotope with an unstable nucleus that decays -- emitting alpha or beta particles, positrons, or gamma rays. As it decays, it loses mass and energy, until a stable isotope develops. For most elements, both stable and radioactive isotopes are known.

Examples of radioisotopes commonly combined with pharmaceutically-active molecules to form radiopharmaceuticals include technetium-99m, gallium-67, Iodine-123, Iodine-13, Thallium-201, Fluorine-18, and Indium-111.

A number of SPECT radiopharmaceuticals incorporate antibody and peptide formulations that can be targeted to specific tissue receptors, allowing one to discriminate healthy from diseased tissue with a high confidence level. However, the more specific the targeting agent is, the more difficult it is to interpret its position anatomically, since there are fewer landmarks.