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A: Magnetic resonance scanning or imaging (MRI) is a method of looking inside the body without using surgery, harmful dyes or x-rays. The MRI scanner uses magnetism and radio waves to produce remarkably clear pictures of the human anatomy. It is one of the most advanced method of diagnostic imaging available in the world today. Although MRI is used for medical diagnosis, it utilizes a physics phenomenon discovered in the 1930s called nuclear magnetic resonance in which magnetic There are two kinds of relaxation times that can be detected and they are known as T1 and T2. When a patient is being scanned with magnetic resonance, the response signals emitted by the atoms in the patient's body are picked up by a very sensitive antenna and forwarded to a computer for processing. When the processing of these signals is complete, a two-dimensional, cross-sectional pattern is created on a monochrome monitor that looks very much like what you would expect if you took a black-and-white TV picture of that particular cross-section. In other words, this shows much more detail than any images generated by X-rays-CAT scans also use X-rays, by the way-but the beauty of MRI is that it doesn't use harmful X-rays. Although this picture looks like a photo, it is not a photo. In fact, in the hands of a trained radiologist, the information it provides is much more useful than what would be revealed in a photo. A typical image is typically made up of 65,000 tiny rectangles that are either white, black or one of a wide range of gray tone values that fall somewhere between black and white. To a trained MRI radiologist, these gray tones speak volumes. |
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Brown University | Brain Science |
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fields and radio waves, both harmless, cause atoms to give off tiny radio signals. In the 1940s, research physicists found that the length of time these response signals are emitted after an atom is stimulated by radio waves varies widely depending upon the substance being examined. This amazing phenomenon also holds true for biological tissue. It wasn't until 1970, however, that the basis for using magnetic resonance as a tool for medical diagnosis when it was found that different kinds of animal tissue emit response signals that vary in length and, furthermore, that cancerous tissue emit response signals that last much longer than non-cancerous tissue. Subsequent findings revealed that the response times of other kinds of diseased tissue, normally called "relaxation times," also vary dramatically.