What Is MRI? How Does MRI Work?

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Main Category: MRI / PET / Ultrasound
Also Included In: Radiology / Nuclear Medicine
Article Date: 16 Apr 2009 - 4:00 PDT

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MRI is short for Magnetic Resonance Imaging. It is a procedure used in hospitals to scan patients and determine the severity of certain injuries. An MRI machine uses a magnetic field and radio waves to create detailed images of the body. Common reasons people go in to get an M.R.I. are for a sprained ankle or back pain.

What should I do to prepare for an MRI?

There is little to no preparation needed before getting an MRI. When you first arrive at the hospital, the doctors will ask you to change into a gown. You will also be asked to remove all accessories such as jewelry, credit cards, and any metallic objects. The reason for this is because MRIs involve magnets, which may interact with objects in your possession. This in turn may lead to bad results and/or poor image quality.

What does an MRI machine look like?

Most MRI machines look like a long tube, with a large magnet present in the circular area. When beginning the process of taking an MRI, the patient is laid down on a table. Then depending on where the MRI needs to be taken, the technician slides a coil to the specific area being imaged. The coil is the part of the machine that receives the MR signal.

Is an MRI going to hurt?

You can breathe a sigh of relief. It is not going to hurt one bit. The exam itself is a painless procedure that is noninvasive, meaning that the body is not tampered with in any way. Since humans are not able to feel any type of radio waves, patients will not feel a thing. A loud tapping noise will be experienced, however, as the magnets are turned on and off throughout the exam. No need to worry, though. If you think the noise will bother you, just ask the technician for a pair of earplugs to drown out the noise.

How long does the MRI test last?

The exam itself takes about 30 - 45 minutes. However, this may vary depending on the number of body parts being examined.

So how does MRI work?

A strong magnetic field is created by passing an electric current through the wire loops. While this is happening, other coils in the magnet send and receive radio waves. This triggers protons in the body to align themselves. Once aligned, radio waves are absorbed by the protons, which stimulate spinning. Energy is released after "exciting" the molecules, which in turn emits energy signals that are picked up by the coil. This information is then sent to a computer which processes all the signals and generates it into an image. The final product is a 3-D image representation of the area being examined.

Unlike CT scanning or general x-ray studies, no ionizing radiation is involved with an MRI.

News on MRI

For the latest news and research on MRI, and to sign up to newsletters or news alerts, please visit our MRI section.

Written by Mathew Kalapurayil
Drake University
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today