The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on April 5, 2021.

Magnetic resonance imaging

What is an MRI

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.

During an MRI, a patient rests on a table and slides into a scanner. A technologist may provide earplugs to dim the sound of the machine. Some imaging tests require a contrast dye to be injected into a vein before the procedure. The contrast material, usually gadolinium, helps certain areas show up better. The procedure is painless and typically takes 30-60 minutes.

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.