Nuclear magnetic resonance imaging--present status.

Nuclear magnetic resonance (NMR) imaging is a new method of imaging the body, and one that does not use ionizing radiation. Nuclei with odd numbers of either neutrons or protons tend to orient themselves along the lines of force in a magnetic field and return to this orientation (precession) after a pulse of radiowaves is applied. In a non-uniform field the radiowaves emitted by the nuclei in returning to their original alignment encodes the spatial distribution of the nuclei. Moreover, the rate of precession provides decay constants defined as the spin-lattice (T1) and spin-spin (T2) time constants which reflect not only upon the atom measured but also upon the chemical milieu in which it exists. Thus not only organ images can be obtained but there is also growing evidence that information about normality and disease in certain tissues may be forthcoming from NMR.