Magnetic Resonance Imaging
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Magnetic Resonance Imaging

(Imaging, Magnetic Resonance; MRI Scan)

En Español (Spanish Version)


Magnetic waves are used to make pictures of the inside of the body. Using a large magnet, radio waves, and a computer, an MRI produces two-dimensional and three-dimensional pictures.

Parts of the Body Involved

Any part of the body

Reasons for Procedure

  • To diagnose internal injuries or conditions
  • To monitor effects of medications and treatments

MRI of Brain Injury

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Risk Factors for Complications During the Procedure

You may not be able to have an MRI exam if you have any of the following in your body:

  • Pacemaker
  • Neurostimulator
  • Ear implant
  • Metal clips in your eyes
  • Implanted port device
  • Intrauterine device (IUD)
  • Metal plate, pins, screws, or surgical staples
  • Metal clips from aneurysm repair
  • Retained bullets
  • Any other large metal objects implanted in your body (Tooth fillings and braces are usually fine.)

Tell your doctor if your work involves metal filings or particles.

What to Expect

Prior to Procedure

In the days leading up to your MRI exam:

  • Avoid using hair gel, spray, lotions, powders, and cosmetics.
  • If your doctor prescribes a sedative:
    • Arrange for a ride home.
    • Do not eat or drink at least 4 hours before the exam.
    • Take the sedative 1-2 hours before the exam, or as directed.

Once at the MRI center:

  • You will be asked about the following:
    • Medical history
    • Pregnancy
    • Allergies
    • Prior head surgery
  • You'll remove any metal objects (eg, jewelry, hearing aids, glasses).
  • An x-ray may be taken to check to see if there are any metal objects in your body.
  • You'll also remove all objects from your pockets.

During Procedure

You may be:

  • Given ear plugs or headphones to wear (The MRI machine makes a loud banging noise.)
  • Given an injection of a contrast dye
  • Allowed to have a family member or friend during the test


None. If you have a fear of enclosed spaces, you may be given a sedative.

Description of the Procedure

You lie very still on a sliding table. Depending on your condition, you may have monitors to track your pulse, heart rate, and breathing. The table is slid into the narrow, enclosed cylinder. (There are also open MRI machines.)

The technician leaves the room. Each of the MRI sequences is performed. Through the intercom, the technician gives you directions, such as to hold your breath. You can talk to the technician through this intercom, as well. If a contrasting dye is used, a small IV needle is inserted into your hand or arm. This is done before you are slid into the machine. First, a saline solution is dripped into your vein to prevent clotting. Then, the dye is injected. When the exam is done, you are slid out of the machine. The IV needle is removed.

After Procedure

You will be asked to wait until the images are examined. The technician may need more images.

How Long Will It Take?

40-90 minutes

Will It Hurt?

The exam is painless. If you have dye injected, there may be stinging when the IV needle is inserted. You may also feel a slight cooling sensation as the dye is injected. If you have a fear of enclosed spaces, the exam may be very difficult for you. Your doctor may have you take a sedative. You can also ask your doctor about an open MRI, which is larger and has openings on all sides.

Possible Complications

Allergic reaction to contrast dye (rare)

Average Hospital Stay


Postoperative Care

  • If you took a sedative, do not drive, operate machinery, or make important decisions until the sedative wears off completely.
  • If you are breastfeeding and receive a contrast dye, wait at least 24 hours after the exam before breastfeeding again.


After the exam, a radiologist will analyze the images and send a report to your doctor. Your doctor will talk to you about the results and any further tests or treatment.

Call Your Doctor If Any of the Following Occurs

  • If you were injected with contrast dye, any allergic or abnormal symptoms
  • Worsening of symptoms that prompted the exam


National Library of Medicine



Health Canada

Public Health Agency of Canada


Gould TA. How MRI works. How Stuff Works website. Available at: . Accessed July 22, 2008.

MRI scans. National Library of Medicine, MedlinePlus website. Available at: Updated July 2008. Accessed July 22, 2008.

University of Iowa, Department of Radiology website. Available at: . Accessed October 14, 2005.

Last reviewed November 2007 by Rosalyn Carson-DeWitt, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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