nuclear magnetic resonance \nu"cle*ar mag*net"ic res"on*ance\ n.
(Physics)
The specific absorption and re-emission of electromagnetic
radiation at characteristic wavelengths by atomic nuclei in a
magnetic field. It is abbreviated NMR. The wavelength of
the radiation absorbed depends on the type of nucleus, the
intensity of the magnetic field, and the local chemical
environment in which the nucleus resides. It is the latter
effect (called the chemical shift), by which atoms of
specific elements in different chemical compounds show a
different resonance frequency, which gives rise to the
greatest utility of this phenomenon in analyzing the chemical
structure of substances. Similar effects of the chemical
environment permit the discrimination of different types of
living tissue by virtue of their different chemical
composition, thus permitting utilization of the phenomenon in
medical diagnostic instruments, especially for magnetic
resonance imaging.
[PJC]
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