Magnetic resonance imaging, or MRI, is based on the fact that atoms contain both positive and negative charges. MRI's use magnetism to use the electrical charges of atoms to create images of materials. The most common use for MRI's is in medical diagnosis. MRI's were available for patients starting in 1984 (Nordenberg, 1999). .

             One of the MRI's greatest advantages is its relative safety compared to some other imaging techniques. The first method for imaging the body, x-rays, which use radiation to create its images. Another advantage is that MRI's can image less dense tissues than x-rays can (Nordenberg, 1999). But where the MRI has a tremendous advantage over x-rays is in its ability to create 3-dimensional images. It also does a better job of showing contrast between dense parts of the body, such as bones, and softer tissue, than other imaging techniques (Nordenberg, 1999). .

             How They Work.

             In medical use, MRI's focus on hydrogen atoms. The magnetic atmosphere the patient enters is a lop-sided one: the magnetic field generated will be stronger one side than the other, resulting in variances in resonance frequency, or how rapidly the hydrogen molecules vibrate in response to the magnetic field (Tro, 2006). That vibration, or resonance, is artificially created and controlled by the very powerful magnets pulling on hydrogen molecules in the body. These patterns are translated by a computer into a detailed image of the body part being imaged. An MRI creates such clear images between dense tissue and softer tissue because softer tissue contains more water, and hence, more hydrogen (Gould, DATE). .

             MRI's actually use four different types of magnets. The first is a resistive magnet. Resistive magnets are made by wrapping coils of wires around a center. An electric current then runs through the center, creating a magnetic field (Gould, DATE). These magnets draw a lot of electricity and are impractical for creating extremely powerful magnets.