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Nuclear Magnetic Resonance or NMR, technique developed in the late 1940s by the Swiss-born United States physicist Felix Bloch for the spectroscopic analysis of substances. In NMR, a substance is placed in a strong magnetic field that affects the spin of the atomic nuclei of certain isotopes of common elements. A radiowave passed through the substance then reorients these nuclei. When the wave is turned off, the nuclei release a pulse of energy that provides data on the molecular structure of the substance and that can be transformed into an image by computer techniques. In the early 1980s, NMR also became a diagnostic tool for obtaining more precise images of tissues within the human body than are possible with CAT scans or ultrasonics (see Radiology). In its medical applications, NMR is now more commonly referred to as magnetic resonance imaging (MRI), in order to avoid the negative connotations of the word "nuclear". MRI does not, in fact, involve radioactivity or other ionizing radiation. MRI is unsurpassed as an imaging technique for scans of the brain, head, and neck. People with metal implants, however, should not be scanned by MRI. In addition, MRI is more expensive than a CAT scan, which is the preferred method of diagnosing bleeding within the brain.
"Nuclear Magnetic Resonance," Microsoft® Encarta® 99 Encyclopedia. © 1993-1998 Microsoft Corporation. All rights reserved.
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