magnetic resonance imaging (MRI), noninvasive diagnostic technique that uses nuclear magnetic resonance magnetic resonance, in physics and chemistry, phenomenon produced by simultaneously applying a steady magnetic field and electromagnetic radiation (usually radio waves) to a sample of atoms and then adjusting the frequency of the radiation and the strength of the
..... Click the link for more information. to produce cross-sectional images of organs and other internal body structures. The patient lies inside a large, hollow cylinder containing a strong electromagnet, which causes the nuclei of certain atoms in the body (especially those of hydrogen) to align magnetically. The patient is then subjected to radio waves, which cause the aligned nuclei to "flip"; when the radio waves are withdrawn the nuclei return to their original positions, emitting radio waves that are then detected by a receiver and translated into a two-dimensional picture by computer. Unhampered by bone and capable of producing images in a variety of planes, MRI is used in the diagnosis of brain tumors and disorders, spinal disorders, multiple sclerosis, and cardiovascular disease. The procedure is considered to be without risk, but the scanner may interfere with pacemakers, hearing aids, or other mechanical devices. Although the images are similar in many ways to those of CAT scans CAT scan (kăt) [computerized axial t
..... Click the link for more information. , they are obtained without X rays or other radiation, and generally provide more contrast between normal and abnormal tissue.

magnetic resonance imaging (MRI)

Computer production of images from magnetic resonance. The structural and biochemical information it provides is helpful in the diagnosis of abnormalities without the possibly harmful effects of X rays or gamma rays. It is invaluable in detecting and delineating tumours and in providing images of the brain, the heart, and other soft-tissue organs. MRI may produce anxiety because the patient must often lie quietly inside a narrow tube. Another disadvantage is that it requires a longer scanning time than other computer-assisted forms of scanning, which makes it more sensitive to motion and of less value in scanning the chest or abdomen. However, MRI images provide better contrast between normal and diseased tissue than those produced by other computer-assisted imagery.