Magnetic resonance imaging

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science.

This page was updated on May 2, 2022.

Magnetic resonance imaging (MRI) is a health care imaging tool designed to create detailed, cross-sectional pictures of the insides of the body. Using radiofrequency waves, powerful magnets and a computer, MRI scans are built to distinguish between normal and diseased tissue.

MRI scanners play an important role in diagnosing cancer, as well as staging and treatment planning. We may be able to use the detailed images from an MRI machine to distinguish between normal tissue and abnormalities. This helps our radiology team to precisely pinpoint how cancerous cells have grown within the body. It also may be useful for revealing metastases, when cancer has spread to a new part of the body. MRI provides greater contrast in the soft tissues of the body than a computed tomography (CT) scan. As a result, radiologists often use the machine for medical imaging involving the brain, spinal cord, muscle, ligaments, blood vessels and the inside of bones.

Specialized MRI machines include functional MRI (fMRI) scanners, which evaluate blood flow in the brain, and open MRI scanners, which can be used for patients with claustrophobia.

Unlike X-rays and CT scans, an MRI does not use ionizing radiation. Instead, MRI uses a strong magnetic field and radio waves. Because of the large magnets, MRI is not recommended for women in the first trimester of pregnancy or for patients who have electronic devices or metal objects in their bodies, such as bullet fragments, shrapnel, cochlear implants, pacemakers or defibrillators.

How to prepare for an MRI

Magnetic resonance imaging, also known as an MRI, is a noninvasive procedure that produces three-dimensional (3D) anatomical images of body parts—for a deeper look than with a standard X-ray. Your doctor may order one to examine soft tissues, muscle, ligaments and tendons, and organs such as the brain.

Before the MRI

  • Block out enough time on test day: The procedure typically takes 45 to 60 minutes, but it may take up to two hours.
  • Dress accordingly: Before the MRI, you’ll likely have to change into a medical gown. Since you’ll be asked to remove any metal for the test, it’s best to leave your jewelry at home.
  • Review instructions for food, drink and daily medications: Ask your care team about any restrictions ahead of test day.
  • Use music for support: When making your appointment, ask whether the facility provides ear plugs or headphones during the test or if you may bring your own. 
  • Keep your medical records organized: If the MRI technologist doesn’t already have your personal and medical history, be prepared to offer details. These may include past scans (for a comparison to new results), surgeries and a list of current medications

During the MRI

  • Be prepared to lie still: To get the most accurate images, you may be asked to lie very still while the designated area of your body is being scanned.
  • Follow directions carefully: The technician may ask you to hold your breath at certain times during the scan to create the clearest images.
  • Don’t be afraid to speak up: It’s not uncommon to feel claustrophobic or anxious during an MRI, so let your technologist know if you’re uncomfortable.
  • Lean on a friend or family member: If you have anxiety, it may help to have a loved one with you for support. Check with the facility to see if there are any restrictions on someone coming with you. 

After the MRI

  • Check in with your doctor about the results: There are typically no side effects or restrictions after an MRI. Sometimes MRI results are delivered in real time to your doctor’s office, but follow up after a few days if you haven’t been told the results. 

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