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How does an MRI work?

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Quick Answer

Magnetic resonance imaging (MRI) is a noninvasive computerized diagnostic technique that uses strong magnetic fields and radio waves to develop an image of the inside of the body, according to Johns Hopkins Medicine. The process does not use potentially dangerous radiation the way that X-rays and CT scans do.

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Full Answer

Patients undergoing an MRI scan usually lie down on a flat pad that is mounted on a sliding track. As the scan begins, the pad is maneuvered into a large metal cylinder that contains high-powered electromagnets. These magnets generate a field around the patient's body, and the scanner begins producing high-frequency radio waves, according to Johns Hopkins Medicine. The magnetic field aligns all of the hydrogen protons in the patient's body along a single axis, which creates a baseline for the scan. As the radio waves pass through the patient's body, they disrupt the alignment of the hydrogen protons, causing them to move slightly out of alignment with the standing magnetic field. As the protons realign themselves to the field, they emit a weak radio signal at a different frequency from the one the MRI is emitting that can be detected by the scanner's sensitive receiver. Fluctuations in the signal coming from the patient's body are fed to the computer for analysis, and an image is then developed from the data.

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