Basic mechanisms that are responsible for the behavior of paramagnetic contrast agents used in MR imaging are discussed. Magnetic properties of matter, including diamagnetism and paramagnetism, are discussed first, followed by a description of the fundamental physical processes that govern the MR relaxation phenomena. The effects of paramagnetic relaxation enhancement are presented in the context of their influence on relaxation mechanisms in tissues. Finally, basic mechanisms by which contrast agents affect the MR signal intensities are reviewed.
