Magnetic resonance imaging (MRI) is a technique that uses a magnetic field and radio waves to create cross-sectional images of your head and body. Your physician can use these detailed, clear images to identify and diagnose a wide range of conditions.

The MRI machine contains a large, cylindrical-shaped magnet with gradient coils that are used to send and receive radio waves. When you're in the machine, the magnet causes all of your water molecules to line up with the magnetic field. In response to the radio waves, your body produces very faint signals. These are picked up by the gradient coils and processed by a computer that makes the images.

The collected data can be used to create a composite, three-dimensional representation of your body. Any two-dimensional plane (slice) can be selected electronically from this representation and displayed on a television-type screen for examination. Photographic images also can be produced from the screen for further viewing and analysis.

These images especially are helpful for examination of the brain, neck, spinal cord and soft tissues. MRI often is used in the diagnosis of central nervous system disorders, such as multiple sclerosis, because of its high-resolution images of the brain and spinal cord's white and gray matter. In addition, MRI can be helpful for evaluating joint, ligament, muscle and bone problems.

There are no known harmful effects from exposure to the magnetic field or radio waves used in making MRI images.

You can eat normally and continue to take your usual medications before this procedure, unless otherwise instructed. You may be asked to remove your street clothes and given a gown and robe to wear or told to wear clothing without metal fasteners, such as sweats. Before the test, you will need to remove all accessories — watch, jewelry, hairpins. Also remove wigs, dentures and hearing aids. This is necessary so that metallic objects in these items won't affect the quality of the MRI picture and to prevent electronic items — watch, hearing aid — from being damaged by the magnets.

Tell the technologist if you have any metal or electronic devices in your body, such as metallic joint prostheses, artificial heart valves, implanted electronic devices, cochlear implants or magnets in your dentures. The presence of metal in your body may be a safety hazard or affect a portion of the MRI image.

You shouldn't receive an MRI scan if you have an implantable cardiac defibrillator or pacemaker. The strong magnetic field produced by the MRI unit may interfere with the pacemaker's function.

If you think you're pregnant, tell the technologist before undergoing MRI imaging because the effects of magnetic fields on fetuses aren't well established.

If you have any questions, ask your physician or MRI technologist.

The MRI machine is a large magnet with a central opening. You'll lie down on a moveable table that slides into the opening of the magnet. Depending on the part of your body to be examined, a small coil may be placed around that portion being examined to receive the MR signal.

A technologist will monitor you from another room, and you will be able to talk with the technologist by microphone. In addition, you may be allowed to have a friend or family member stay in the room with you.

The MRI machine creates a strong magnetic field around you, and radio waves are directed at your body. You will not feel the magnetic field or radio waves, and there are no moving parts around you.

You will hear repetitive tapping, thumping sounds or other noises during the MRI scan. These sounds come from the internal part of the magnet. Ear-plugs or music may be provided to help block the noise.

An MRI examination can take between 30 and 90 minutes. While the scan is taking place, breathe quietly but comfortably, without moving your head or body. Most people find that after several minutes of imaging they become quite relaxed and have few problems lying still for the duration of the examination. If you have a hard time lying still for the required period of time or are anxious about the enclosed space, you may be given a sedative. Some MRI units may be wider, shorter or open on all sides, which may be more comfortable for you. However, the quality of images taken from these systems may vary.

In some cases contrast agents are injected into your veins to enhance certain tissues or blood vessels in the images. These will be inserted into an arm or hand vein with the use of a needle connected to an intravenous line. These contrast agents are different than those used in kidney tests or computerized tomography (CT) scanning. They don't contain iodine and are less likely to cause an allergic reaction.

When the examination is finished, you may be asked to wait until the images are reviewed to make sure that no additional imaging is necessary. At that point, you may leave and resume your regular activities. A radiologist will review the images made during your examination and report the findings to your physician.

Your radiologist will review the MRI images for irregularities of various structures within your body, including:

• Abnormal size or position of organs, bones, blood vessels or soft tissue structures
• Presence of growths or lesions
• Blood flow
• Organ function

Your doctor may recommend that you have an MRI examination to identify and diagnose a variety of ailments, including:

Head	Identify brain tumors, strokes, and chronic disorders of the nervous system, such as multiple sclerosis Reveal brain abnormalities in people with dementia Diagnose diseases of the pituitary gland Locate tissue abnormalities in people with eye or inner ear diseases
Cardiovascular	Identify damage caused by heart attack or heart disease Detect plaques and blockages of the blood vessels
Musculoskeletal	Identify and diagnose damage to the tissues in and near the bones and joints Identify infections, injuries, degenerative disorders and tumors of the bones and joints
Body	Reveal tumors and functional disorders in organs of the chest or abdomen, such as lungs, liver, pancreas, kidney and spleen Detect breast cancer and problems of the male and female reproductive systems and bladder

Pros

• Test is painless
• No radiation or harmful side effects
• Noninvasive method of viewing the insides of the body
• Can provide images from multiple viewpoints and is effective at differentiating between various soft tissues
• Covered by most insurance companies
• Provides images of organs that otherwise would be obscured by bones or foreign bodies
• Performed on an outpatient basis

Cons

• May be uncomfortable for people who don't like confined spaces or have claustrophobia
• Expensive tests — more expensive than X-rays or CT scans
• Test can be time-consuming
• Test can be affected by body movement
• Can't be used on people with some implanted metal objects, such as pacemakers

An estimated cost range for an MRI is $860 to $2,000. Most insurance programs usually cover this test. However, scans of certain parts of the body or for some medical conditions may not be covered. Check with your personal insurance company to see if your test will be covered.