Magnetic resonance imaging (MRI) of the brain is a safe and painless test that
uses a magnetic field and radio waves to produce detailed images of the brain and
the brain stem. An MRI differs from a CAT scan (also called a CT scan or a computed
axial tomography scan) because it does not 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 machines that have larger openings and are helpful for patients with
claustrophobia. MRI machines are located in hospitals and radiology centers.
During the exam, 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 pinpoint problems in the brain and the brain stem
when the scan focuses on those areas.
Why It's Done
MRI can detect a variety of conditions of the brain such as cysts, tumors, bleeding,
swelling, developmental and structural abnormalities, infections, inflammatory conditions,
or problems with the blood vessels. It can determine if a shunt is working and detect
damage to the brain caused by an injury or a stroke.
MRI of the brain can be useful in evaluating problems such as persistent headaches,
dizziness, weakness, and blurry vision or seizures, and it can help to detect certain
chronic diseases of the nervous system, such as multiple sclerosis.
In some cases, MRI can provide clear images of parts of the brain that can't be
seen as well with an X-ray, CAT scan, or ultrasound, making it particularly valuable
for diagnosing problems with the pituitary gland and brain stem.
In many cases, a brain MRI requires no special preparation. However, the technician
will have your child remove any objects containing metal (such as eyeglasses and jewelry)
because they can produce a bright or blank spot on the diagnostic film. 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. Electronic devices aren't permitted in the MRI room.
To get the highest quality MRI results, your child will need to lie still during
the scan. For this reason, sedation may be needed, especially for babies and young
kids, who often have trouble staying still for the test. Sedation is also helpful
for kids who have trouble relaxing in an enclosed space (claustrophobia).
Sedation medicines usually are given through an intravenous (IV) line (small tube
in a vein) to help a child stay asleep during the entire test.
If your child will be sedated, food and liquids will be stopped at a certain
point before the MRI to allow the stomach to empty. It's important to notify the MRI
technician of any illness, allergy, previous drug reactions, or pregnancy.
You can stay in the MRI room with your child until the test begins, and some centers
let parents stay throughout the test. Otherwise, you'll join the technician in
an outer room or be asked to stay in a waiting room.
An MRI of the brain usually takes 30-45 minutes to perform. Your child will lie
on the movable scanning table while the technologist places him or her into position.
A special plastic device called a coil may be placed around your child's head. The
table will slide into the tunnel and the technician will take images of the head.
Each scan takes a few minutes.
To detect specific problems, your child may be given a contrast solution
through an IV. The solution is painless as it goes into the vein. The contrast highlights
certain areas of the brain, such as blood vessels, so doctors can see more detail
in specific areas. 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 and
will be connected to a machine that checks the heartbeat, breathing, and oxygen level.
Once 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
An MRI exam is painless. Your child may have to lie still on the MRI table for
30-45 minutes during the procedure, but there are brief breaks between each scan.
If your child feels cold lying on the MRI table, a blanket can be provided.
Unless sedation was used or you are told otherwise, your child can immediately
return to normal routines and diet. Most sedation wears off within 1-2 hours, and
any contrast material given should pass through the body in about 24 hours.
Getting the Results
The MRI images will be viewed by a radiologist who's specially trained in interpreting
the scans. The radiologist will send a report to your doctor, who'll 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. If the MRI was done on an emergency
basis, the results can be made available quickly.
MRIs are safe and relatively easy. No health risks are 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, you may discuss the risks and benefits of sedation
with your provider. 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 on hand 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 to explain that pictures of the head will be taken
and that the equipment will probably make knocking and buzzing noises.
It also may help to remind your child that you'll be nearby during the entire test.
If an injection of contrast fluid or sedation is needed, 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
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.