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How does MRI work?

Photo: Becky Stern via Flickr

MRI, or magnetic resonance imaging, is a test that uses both a magnetic field and radio waves to reveal details of the body’s internal structures without radiation. It’s known for the clear, detailed images it’s able to provide and for its utility in diagnosing injuries to joint structures, soft tissues and bones, as well as brain and internal organ diseases.

Invented in the 1970s, the MRI has proved itself useful over time. The 1 million-plus MRI scans occurring each week worldwide use radio waves sent out during the scan to help manipulate the magnetic position of one of the body’s basic building blocks – the hydrogen atom. These positions are then measured by an antenna and sent to a computer to be translated into an image.

The result is a black-and-white picture of a cross-section of the body called a “slice”. Slices are acquired in three directions (up-down, side-to-side and front-to-back) to create a complete, three-dimensional picture of the internal structure in question.

Most standard imaging magnets today have strengths of 1.5 or 3 Tesla and send back a standard number of slices. The University of Minnesota’s Center for Magnetic Resonance Research, however, uses a 7 or 9.4 Tesla magnet to examine internal human structures such as cartilage. The additional power means a higher picture resolution and more clearly visible detail for the viewer, creating a more precise image.

That means that when doctors like University of Minnesota Physicians sports medicine specialist Elizabeth Arendt, M.D., a professor in the U of M Department of Orthopaedic Surgery and fellow researchers need details to examine such things as the very small area between bone structures where cartilage lies, details including the earliest signs of cartilage degeneration can be seen more clearly than ever before.

Want to learn more about arthritis research powered by a more powerful MRI? Be sure to check out this Health Talk post.


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