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Magnetic Resonance Imaging
What is it? Overview Usage Side Effects and Warnings

Magnetic Resonance Imaging Overview

Written by FoundHealth.


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

What to Expect

Prior to Test

If your doctor prescribes a sedative:

  • Arrange for a ride home.
  • Do not eat or drink for at least four hours before the exam.
  • Take the sedative 1-2 hours before the exam, or as directed.

At the MRI center:

  • You will be asked about the following:
  • Medical and surgical history
  • Pregnancy
  • Allergies
  • Other conditions that you may have—If your MRI involves contrast material, your doctor will ask about the health of your kidneys. There is a risk of complications in people who have kidney disease and receive contrast material.
  • You will be asked if you have something in your body that would interfere with the MRI, such as:
  • Pacemaker or implantable defibrillator
  • Neurostimulator
  • Ear implant
  • Metal fragments in your eyes or in any other part of your body (Tell your doctor if your work involves metal filings or particles.)
  • Implanted port device, such as an insulin pump
  • Metal plate, pins, screws, or surgical staples
  • Metal clips from aneurysm repair
  • Retained bullets
  • Any other large metal objects in your body (Tooth fillings and braces are usually fine.)
  • You will be asked to remove any metal objects (eg, jewelry, hearing aids, glasses).
  • You will also be asked to remove all medicine skin patches (eg, Duragesic patch). They may contain metal elements and cause skin burns.
  • An x-ray may be taken to check for any metal objects in your body.

You may be:

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

Description of Test

You will 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 will slide into a narrow, enclosed cylinder. In some machines, the sides are open, so you can look out into the room.

If a contrast dye is used, a small IV needle is inserted into your hand or arm before you slide into the machine. First, a saline solution is dripped into your vein to prevent clotting. Then, the dye is injected. You might have an allergic reaction to the dye, but this is rare.

The technician will leave the room. Through the intercom, the technician will give you directions, such as to hold your breath. You can talk to the technician through this intercom as well. The technician will take the pictures. When the exam is done, you will slide out of the machine. If you have an IV needle, it will be removed.

If you are claustrophobic or unable to lie on a flat table, there are open MRI machines available. They allow you to have the test done without being put in a narrow cylinder. There are also MRI machines that allow a patient to be in a sitting position. This may be important for patients with concerns, like a painful back.

After Test

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

If you took a sedative, do not drive, operate machinery, or make important decisions until it wears off completely.

If you are breastfeeding and receive a contrast dye, you and your doctor should discuss when you should restart breastfeeding. Information available has not found any ill effects to the baby of a breastfeeding mother who has had contrast dye.

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 hard 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.


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.



National Library of Medicine



Health Canada

Public Health Agency of Canada


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

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Kanal E, Barkovich A.J., Bell C, et al. ACR Guidance Document for Safe MR Practices: 2007. AJR 2007; 188:1–27

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