The use of nuclear magnetic resonance (nmr) techniques in imaging the internal structure and metabolic reactions of the body. Hydrogen, the most common element in the body, appears in the complex biomolecules that are the constituents of all bodily tissues, such as healthy brain tissue, bone, tumors, or blood. In each case the nature and density of the hydrogen-bearing molecules and the local chemical environment will cause the NMR spectrum to vary slightly from that of pure hydrogen, allowing the identification of tissue types and even the monitoring of chemical activity. Spatial information can be obtained by purposely distorting the static magnetic field with extra “gradient” fields; the resultant field conditions permit resonance to occur only in a carefully defined region which, for different purposes, may be a three-dimensional volume, a plane, a line segment, or even a point. The NMR signal, encoded in this way, can be computer reconstructed into a cross-sectional image that reveals anatomical features with a spatial resolution rivaling or exceeding that obtainable with x rays.
A diagnostic technique for creating cross-sectional images of the body by the use of nuclear magnetic resonance (NMR). NMRI can also provide information on tissue biochemical activity. The procedure is noninvasive. The device used is called an NMRI (or MRI) scanner.