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Also called NMR . magnetic resonance imaging: a noninvasive diagnostic procedure employing an MR scanner to obtain detailed sectional images of the internal structure of the body.
magnetic resonance imager. See MR scanner.
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Words nearby MRI

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

How to use MRI in a sentence

British Dictionary definitions for MRI


abbreviation for
magnetic resonance imaging
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for MRI


magnetic resonance imaging
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for MRI

[ ĕm′är′ī ]

Short for magnetic resonance imaging. The use of nuclear magnetic resonance to produce images of the molecules that make up a substance, especially the soft tissues of the human body. Magnetic resonance imaging is used in medicine to diagnose disorders of body structures that do not show up well on x-rays. See more at nuclear magnetic resonance.

A Closer Look

A picture is worth a thousand words, and nowhere is this more apparent than in the powerful diagnostic technique known as magnetic resonance imaging (MRI), which has revolutionized many areas of medicine. Compared to imaging techniques that use x-rays, such as computerized axial tomography (CAT), MRI generates far more detailed three-dimensional images of the soft tissues of the body, especially of the nervous system from the brain to the spine. These images greatly improve the ability of doctors to distinguish abnormal from healthy tissues. MRI can also be used to observe and measure dynamic physiological changes inside a patient without cutting into or penetrating the body. To produce an image, an MRI machine uses a powerful magnet to generate a magnetic field. When a patient lies within this field, the nuclei of atoms within the body align themselves with the magnetic field (much as iron filings line up around a magnet). Radio waves are then pulsed through the body, causing the nuclei to change their alignment with respect to the axis of the magnetic lines of force. As they return to their previous state after each pulse, they produce faint, distinctive radio signals; the rate at which they emit signals and the frequency of the signals depend on the type of atom, the temperature, the chemical environment, position, and other factors. These signals are detected by coils around the body and processed by a computer to produce images of internal structures. MRI holds yet another significant advantage over CAT in that exposure to potentially harmful x-ray radiation is avoided.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.