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.
An MRI differs from a CAT scan (also called a CT scan or a computed axial tomography
scan) because it doesn't use radiation.
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 scanners that have larger openings and are helpful for patients with
claustrophobia. MRI scanners 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. These images help 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. MRI is 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 intravenous (IV) line (actually a 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 technician will ask if your child is allergic to any medications or food before
the contrast solution is given. The contrast solution used in MRI tests is generally
safe. However, allergic reactions can occur. Talk to your doctor about the benefits
and risks of receiving contrast solution in your child's case.
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, discuss the risks and benefits of sedation with
your doctor. Also, because contrast solutions can cause allergic reactions in some
kids, be sure to check with your doctor before your child receives any solution. There
should be medical staff available who are prepared to handle an allergic
If your child has decreased kidney function, this is an important medical condition
to discuss with the radiologist and technician before receiving IV contrast since
it may lead to some rare complications.
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.