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 ]