Magnetic resonance imaging (MRI)

Description
Magnetic resonance imaging (MRI) is a diagnostic technique used to produce images of structures inside the body.

Purpose/indications
MRI scans can help doctors detect diseases and evaluate injuries or anatomic abnormalities throughout the body, as well as monitor the progress of a disease or treatment. An MRI scan can help doctors evaluate:
the blood vessels and heart
the head and neck
the spinal cord
the breasts
the prostate gland
the bones, joints, bone marrow, ligaments, cartilage, muscles and tendons
abdominal and pelvic masses
certain organs, including the liver, lungs, kidneys, adrenal glands, thyroid gland and ovaries
Contrast agents (substances that will appear on the MRI images) given through a vein may be used to help doctors see blood vessels and make diagnoses without using studies that require radiation.


Patient preparation
If you're not comfortable in confined spaces, discuss options for managing anxiety with your doctor before scheduling the exam. Find out how long the procedure will last. (Depending on the area of your body being studied, the scan may take 30 to 90 minutes.) Finally, ask if you can bring tapes or CDs to listen to during the procedure to help you relax.
If your test will involve a contrast material, your doctor or the radiology staff will give you specific instructions to follow before the procedure concerning intake of food or fluids. Discuss any questions or concerns you have about the contrast material before the exam. Remember to tell your doctor about any allergies.

On the day of your MRI scan, wear comfortable clothing without metal zippers, hooks or closures. Don't wear any jewelry, watches, metal hair clips, cosmetics containing metallic flecks or any other metallic objects. Credit cards with magnetic strips will be erased if taken into the MRI area.

For your own comfort, use the bathroom before the procedure begins. If you're claustrophobic, remind your doctor and the radiology staff when you arrive at the medical facility. If you plan to receive sedation before the procedure, arrange to have someone drive you home afterward.

Parents of a child having an MRI may be able to stay with the child during the scan. Discuss your request with your doctor or the radiology staff.


Procedure
Magnetic resonance imaging uses a strong magnetic field, radio waves and a computer to produce a picture. First, you'll be asked to lie still on a table. The table will be placed inside a machine shaped like a tube, unless you have an open MRI which allows parts of your body to remain outside of a tube. (A new generation of machine that allows you to stand during the procedure is available in a few locations for certain types of MRI scans. Your doctor will determine which type of MRI -- closed, open or standing -- will be used for your scan.) The machine creates a magnetic field that surrounds your body. Then, you'll be exposed to painless radio waves that cause your body to give off energy. This energy allows the computer to make detailed pictures of your internal structures.
It's important to remain completely still. Any movement can disturb the images that are being made. During the test, you'll be able to speak to the staff through earphones or a microphone. You may also view the staff through a screen above your eyes. You may feel a slight warm sensation in your teeth if you have metal fillings. You may also hear loud noises.


Postprocedure care
The MRI scan will be read by a radiologist. Be sure to discuss the test results with your doctor. You may also want to ask for a consultation with a radiologist.

Benefits
Magnetic resonance imaging has a variety of benefits:
MRI has no known side effects, and there is no exposure to radiation.
It's a noninvasive, painless procedure.
Unless you receive medication to alleviate anxiety, you can drive yourself home after the procedure.
MRI can discriminate soft tissue contrast (gray and white brain matter, for example) more effectively than X-ray based diagnostic techniques.
MRI is unrivaled in its ability to view three-dimensional images of body surfaces (planes) without repositioning the patient.
Thanks to the precise images MRI can produce, diagnostic surgery such as arthroscopy may not be necessary. If you do need surgery, MRI can help the surgeon plan the best approach.

Risks
People who have any type of metal implant (such as a pacemaker, surgical clips, artificial metal joints, certain types of artificial heart valves, spinal cord stimulators, infusion pumps, cardiac monitoring equipment, cochlear implants or shrapnel) cannot use MRI. The magnetic field may move the implanted metal and cause injury or even death. The metal can also distort the image obtained by MRI. If you have an implanted device, discuss the safety of MRI with your doctor or radiologist. Rarely, an allergic reaction may occur if a contrast agent is used.

Considerations
In some cases, MRI may not be the best imaging procedure. Always discuss the options with your doctor. Here are some things to keep in mind:
People who need ventilators to breathe (or other continuous monitoring devices) can't use MRI.

Although antianxiety medication can help, some people may be too claustrophobic to be placed into a closed MRI machine. Open-sided MRI machines are available, but not in all areas.

People who are extremely overweight may not fit into a traditional MRI machine. Again, open-sided MRI machines may not be available in all areas.

To get an accurate image, young children may need to be sedated before the procedure.

Compared to other types of diagnostic tests, MRI can take a long time.

MRI is expensive. Ask your insurance company about coverage before you schedule the exam.

Pregnancy-specific information
Researchers are still not entirely certain about the effects of MRI on a developing fetus. For now, some recommend avoiding MRI during the first trimester. The decision should be based on individual clinical considerations.

Senior-specific information
For older adults, MRI is commonly done without problems.