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What Happens During an MRI?


Updated January 25, 2009


The patient lies on a table that rolls into the MRI machine

Photo © A.D.A.M.
Question: What Happens During an MRI?
Answer: Magnetic resonance imaging (MRI) uses a large magnet, radio waves and a sophisticated computer to generate images of organs and structures inside the body. It does not use radiation like an x-ray.

For an MRI, you will lie on a table that slides inside a tunnel in a large machine. The technician will position you to prepare you for the best images. Dye may be injected into your vein to help make clearer images. During the test, the magnet in the machine moves from side to side and makes humming, bumping, or banging sounds. This is very noisy, so you may wear earplugs. The test takes a long time (about an hour), and you must lie still the entire time. An MRI is painless, but some people find it difficult to lie still in the tunnel. As such, sedative medication is sometimes given prior to the test to relax the patient.

There is an intercom speaker in the scanner, so you can speak to the person operating the machine while the images are being taken. Some MRI scanners have televisions and special headphones you can use during the scan.

Tell your doctor and/or radiologist if you have any of the following metal objects in your body because you cannot have an MRI:

  • Implanted cardiac pacemaker
  • Inner ear (cochlear) implants
  • Certain brain aneurysm clips
The following objects may also preclude an MRI, depending on the type of metal, length of time it has been in the body, and loaction relative to the area of interest for the scan:
  • Shrapnel or bullet fragments
  • Recently placed artificial joints
  • Certain artificial heart valves
  • Older vascular stents
  • Implanted medication pump (like for insulin or pain medicine)
Pregnant women also should not get an MRI unless it is medically urgent.
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