Magnetic Resonance Imaging

Magnetic Resonance Imaging (MRI) is a diagnostic procedure that uses a combination of a large magnet, radio frequencies and a computer to produce detailed images of organs and structures within the body.

An MRI is often used to examine the heart, brain, liver, pancreas, male and female reproductive organs, and other soft tissues, to assess blood flow, to detect tumor and diagnose many forms of cancer, to evaluate infections, and to assess injuries to bones and joints.

MRI can be performed on an outpatient basis, or as part of inpatient care. The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around you. This magnetic field, along with a radio frequency, alters the hydrogen atoms' natural alignment in your body. Computers are then used to form 2-dimensional images of a body structure or organ based on the activity of the hydrogen atoms. Cross-sectional views can be obtained to reveal further details. MRI does not use radiation, as do x-rays or CT scans

Preparation for the procedure

No preparatory tests, diets or medications are usually needed. An MRI can be performed right after other imaging studies. Depending on what area of your body is being imaged you may be asked to fast for four to six hours before the scan.

Because of the strong magnets, certain metal objects are not allowed in the room. Items such as jewelry, watches, credit cards and hearing aids can be damaged. Pins, hairpins, metal zippers, and similar metallic items can distort the images.

Removable dental work should be taken out just before the scan. Pens, pocketknives and eyeglasses can become dangerous projectiles when the magnet is activated and should not accompany you into the scanner area. If you wear a cardiac pacemaker you cannot be scanned and should not enter the MRI area because the strong magnetic fields can displace or disrupt the action of the unit.

If you have metal objects in your body you cannot be scanned. Such objects include: Inner ear (cochlear) implants, brain aneurysm clips, some artificial heart valves.

For a more in depth look at this procedure, visit our Health Library page on this topic.