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Definitions of what an MRI or Magnetic Resonance Imaging scan is in definitions and pictures.

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In words:

What is an MRI or Magnetic Resonance Imaging scan?

An MRI (or magnetic resonance imaging) scan is a painless radiology technique that has the distinct advantage of avoiding any form of x-ray radiation exposure. By using a strong magnetic field and pulses of radio waves to make images of structures inside the body, an MRI scan prevents a person from any exposure to X-Rays or any other damaging forms of radiation.

The MRI scanner itself is a tube surrounded by a giant circular magnet. A patient lies on a moveable bed that is inserted into this magnet. Our body consists mainly of water, and water contains hydrogen atoms. Radio waves 10,000 to 30,000 times stronger than the magnetic field of the earth are then sent through the body. This affects the body's hydrogen atoms, forcing the nuclei into a different position.

As the nuclei move back into place they send out radio waves of their own. The scanner picks up these signals and a computer turns them into a picture. This information is processed by a computer, and an MRI image is produced.

Using an MRI scanner, it is possible to make very detailed images of almost all the tissue in the body. The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter.  It is even possible to gather data about the different types of tissues by changing the timing of the radiowave pulses.

MRI scans have been used since the beginning of the 1980s and may show problems that cannot be seen with other imaging methods. In many cases, MRI scans can give different information about structures in the body than can’t be seen with an X-ray, ultrasound, or computed tomography (CT) scans.

For some procedures, contrast agents, such as gadolinium, are used to increase the accuracy of the images.

MRI tests are usually done by MRI technologists. The images are usually interpreted by a radiologist, but some other types of qualified doctors can also interpret MRI scans.

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Brain MRI - pineal cyst two-views

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