What It Is
Magnetic resonance imaging (MRI) is a safe and painless test that uses a magnetic field and radio waves to produce detailed pictures of the body's organs and structures. MRI doesn't use radiation, one way that it differs from a CAT scan (also called a CT scan or a computed axial tomography scan).
An MRI scanner consists of a large doughnut-shaped magnet that often has a tunnel in the center. Patients are placed on a table that slides into the tunnel. Some centers have open MRI machines that have larger openings and are helpful for patients with claustrophobia. MRI machines are located in hospitals and radiology centers.
During the examination, radio waves manipulate the magnetic position of the atoms of the body, which are picked up by a powerful antenna and sent to a computer. The computer performs millions of calculations, resulting in clear, cross-sectional black-and-white images of the body. These images can be converted into three-dimensional (3-D) pictures of the scanned area. This helps to pinpoint problems in the body.
Why It's Done
MRI is used to detect a variety of conditions, including problems of the brain, spinal cord, skeleton, chest, lungs, abdomen, pelvis, wrists, hands, ankles, and feet. In some cases, it can provide clear images of body parts that can't be seen as well with an X-ray, CAT scan, or ultrasound, making it particularly valuable for diagnosing problems with the eyes, ears, heart, and circulatory system.
An MRI's ability to highlight contrasts in soft tissue makes it useful in deciphering problems with joints, cartilage, ligaments, and tendons. MRI can also be used to identify infections and inflammatory conditions or to rule out problems such as tumors.
In many cases, undergoing an MRI requires no special preparation. However, metallic objects often produce a bright or blank spot on the diagnostic film. The technician will have your child remove any objects containing metal, such as eyeglasses, jewelry, belts, or credit cards. Electronic devices are not permitted in the MRI room. Braces and dental fillings won't interfere with the scan. You'll also be asked questions to make sure your child doesn't have any internal metal clips from previous surgery or anything else that might cause a problem near a strong magnetic field.
To obtain the highest quality MRI results, your child will need to be completely still during the scan. For this reason, sedation may be required during the MRI. This is common in infants and young kids. If sedation is needed, food and liquids will be stopped at a certain point before the MRI to allow your child's stomach to empty. It's important to notify the MRI technician of any illness, allergy, previous drug reactions, or pregnancy.
For young kids who are likely to have difficulty staying still for the test, sedation medications are usually given through an IV line (intravenous tube) to help them stay asleep during the entire test. Sedation is also helpful if a child is claustrophobic. To relieve anxiety before and during the test, some patients take an oral sedative on the way to the hospital or radiology center.
You can stay in the MRI room with your child until the test begins, and in some centers you may be permitted to stay throughout the test. If you don't stay in the room, you'll join the technician in an adjacent room or be asked to stay in a waiting room. If you're nearby, you'll be able to watch through a window and talk to your child through an intercom during breaks between scans. This can soothe your child if he or she is awake in the MRI machine.
An MRI exam usually takes 20-90 minutes to perform, depending on the type of study being performed. Your child will lie on the movable scanning table while the technologist places him or her into position. The table will slide into the tunnel and the technician will take images. Each scan will last a few minutes.
To detect specific problems, your child may be given a contrast solution through an IV. The solution, which is painless as it goes into the vein, highlights certain areas of the body, such as blood vessels, so doctors can see them in more detail. The contrast solution used in MRI tests is safe, and allergic reactions are very rare. The technician will ask if your child is allergic to any medications or food before the contrast solution is given.
As the exam proceeds, your child will hear repetitive sounds from the machine, which are normal. Your child may be given headphones to listen to music or earplugs to block the noise and will have access to a call button in case he or she becomes uneasy during the test. If sedated, your child will be monitored at all times by a machine that checks the heartbeat, breathing, and oxygen level.
When the exam is over, the technician will help your child off the table; if sedation was used, your child may be moved to a recovery area.
What to Expect
MRIs are painless. Your child may have to lie still on the MRI table for 20-90 minutes during the procedure, but there are brief breaks between each scan. Unless sedation is used or you're told otherwise, your child can immediately return to normal routines and diet.
If your child feels cold lying on the MRI table, a blanket can be provided. Most sedation will wear off within 1-2 hours, and any contrast material given should pass through the body in about 24 hours.
Getting the Results
MRI images will be viewed by a radiologist who's specially trained in reading and interpreting the scans. The radiologist will send a report to your doctor, who will discuss the results with you and explain what they mean. In most cases, results can't be given directly to the patient or family at the time of the test.
MRIs are safe and easy. No health risks have been associated with the magnetic field or radio waves, since the low-energy radio waves use no radiation. The procedure can be repeated without side effects.
If your child requires sedation, there's a slight chance of slowed breathing due to the medications. If there are any problems with the sedation, the MRI staff can treat them right away. Allergic reactions to the contrast solution are rare, and the technician and other staff are prepared to handle such cases.
Helping Your Child
You can help your child prepare for an MRI by explaining the test in simple terms before the examination. Make sure you explain what part of the body will be examined and that the equipment will probably make knocking and buzzing noises.
It may also help to remind your child that you'll be nearby during the entire test.
If an injection of contrast fluid is required, you can tell your child that the initial sting of the needle will be brief and that the test itself is painless.
If your child will be awake for the test, be sure to explain the importance of lying still. Your doctor may suggest that you and your child take a tour of the MRI room before the test.
If You Have Questions
If you have questions about the MRI procedure, speak with your doctor. You can also talk to the MRI technician before the exam.
Reviewed by: Kate M. Cronan, MD
Date reviewed: October 2008