n. (Physics) A phenomenon resulting from quantization in the magnetic field of electrons or atoms or molecules or nuclei exposed to an external magnetic field, by which a narrow frequency band of radio waves may be absorbed and re-emitted by the object. [ WordNet 1.5 +PJC ]

n. (Medicine) a medical diagnostic procedure utilizing the phenomenon of nuclear magnetic resonance to generate images of internal parts of the body. It depends on the differential absorption of electromagnetic radiation by different types of living tissue in a magnetic field. It is complementary to X-ray imaging in that the softer tissue show more prominently in magnetic resonance images, rather than bone, as with X-rays. It is a non-invasive procedure, allowing such images to be obtained without penetration of the tissue by objects. It is abbreviated MRI. As with computerized tomography, the results are usually presented as images of sequential planar sections of that part of the body of concern to the physician. [ PJC ]

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 ]

n. (Physics) The resonance absorption of a gamma ray by a nucleus identical to the nucleus that emitted the gamma ray. [ WordNet 1.5 ]

n. [ Cf. F. résonance, L. resonantia an echo. ] 1. The act of resounding; the quality or state of being resonant. [ 1913 Webster ]

2. (Acoustics) A prolongation or increase of any sound, either by reflection, as in a cavern or apartment the walls of which are not distant enough to return a distinct echo, or by the production of vibrations in other bodies, as a sounding-board, or the bodies of musical instruments. [ 1913 Webster ]

3. (Physics) A phenomenon in which a vibration or other cyclic process (such as tide cycles) of large amplitude is produced by smaller impulses, when the frequency of the external impulses is close to that of the natural cycling frequency of the process in that system. The shattering of a glass object when impinged upon by sound of a certain frequency is one example of this phenomenon; another is the very large tides in certain basins such as that of the Bay of Fundy, which has a natural cycling frequency close to that of the tidal cycle. [ PJC ]

4. (Electronics) An electric phenomenon corresponding to that of acoustic resonance, due to the existance of certain relations of the capacity, inductance, resistance, and frequency of an alternating circuit; the tuning of a radio transmitter or receiver to send or detect waves of specific frequencies depends on this phenomenon. [ Webster 1913 Suppl. +PJC ]

Pulmonary resonance (Med.), the sound heard on percussing over the lungs. --
Vocal resonance (Med.), the sound transmitted to the ear when auscultation is made while the patient is speaking. [ 1913 Webster ]