Magnetic resonance imaging (MRI) is a diagnostic imaging procedure that
uses radio waves, a magnetic field, and a computer to generate images of
MRI is used to visualize the body to assist doctors in their efforts to
diagnose certain diseases or conditions and to evaluate injuries. For
pediatric imaging, MRI is used for a variety of purposes, including the
MRI provides images with excellent contrast that allow clinicians to
clearly see details of soft tissue, bone, joints, and ligaments. MRI
angiography is an imaging technique used to evaluate the blood vessels,
for example, to detect aneurysms or cardiovascular problems. Because MRI
does not use ionizing radiation to produce images, like x ray and CT, it
is often the examination of choice for pediatric imaging and for imaging
the male and female reproductive systems, pelvis and hips, and urinary
tract and bladder.
MRI can also be used to evaluate brain function for assessing language,
senses, neurologic disorders, and
. This technique, called functional MRI, involves rapid imaging to display
changes in the brain's blood flow in response to tasks or visual
and auditory stimuli. Functional MRI is being researched to image
neurologic disorders, such as attention deficit hyperactivity disorder
, and epilepsy.
MRI spectroscopy is another emerging imaging technique for evaluating
pediatric brain disorders. In MRI spectroscopy, chemicals in the brain are
measured and brain tissue is imaged. This technique is being investigated
to evaluate traumatic brain injury, speech delay, creatine deficiency
in young children.
Interventional and intraoperative MRI is another developing field that
involves performing interventional procedures, primarily brain surgeries,
using a specially designed MRI unit in an operating room.
Magnetic resonance imaging (MRI) of a fetus.
(© Lester Lefkowitz/Corbis.)
MRI is performed using a specialized scanner, a patient table, systems
that generate radio waves and magnetic fields, and a computer workstation.
The scanner, which is usually shaped like a large rectangle with a hole in
the center, contains the systems that generate the magnetic field. A
motorized and computer-controlled patient table moves into the
scanner's center hole during the scan. A technologist operates the
MRI scanner from an adjacent control room that contains a computer system
and an intercom system for communicating with the patient during the scan.
In most MRI scanners, the patient opening is like a long tube, and some
patients may become claustrophobic. To be more patient-friendly, different
types of MRI scanners have been developed. Newer MRI scanners have shorter
patient openings that allows the patient's head to remain outside
the machine during body scans. Open MRI scanners are available with
columns and open sides to alleviate claustrophobia.
Depending on the body area being scanned, special body coils may be used
to enhance the images. These coils are foam and plastic braces or
wraparound pads that are placed on the body part being imaged. For head
imaging, the coil may be shaped like a head or neck rest.
Children undergoing an MRI scan are appropriately positioned on the
patient table by the technologist. For some scans, an injected contrast
material may be used and is administered using an intravenous catheter.
Once the patient is positioned, the technologist goes to an adjacent
control room to operate the scanner. The technologist uses an intercom
system to instruct the child to hold their breath or remain still at
certain times during the scan. Scans range from 30 minutes to 90 minutes,
depending on the type of scan. When the MRI machine is scanning, the child
hears loud clanging and whirring noises. To alleviate
or stress related to hearing this noise and being in the small scanning
tube, the child may be offered earplugs or specially designed head phones
for listening to music. Centers that specialize in pediatric imaging often
also have special video goggles so that the child can watch a cartoon or
movie during the scan. For infants, neonatal noise guards—special
padded ear shields—are available.
MRI scans are performed in a hospital radiology department for inpatients
and emergency cases. For scans requested by a physician, the MRI
examination can be performed in the hospital radiology department on an
outpatient basis or in an imaging center. Hospitals that do not have their
own MRI systems may schedule MRI scans by contracting with a company that
brings an MRI scanner in a specially designed mobile trailer. Mobile MRI
services are frequently used in rural areas. For some conditions, such as
orthopedic disorders or injuries, an MRI may be performed in a
physician's office using a small MRI unit called an extremity MRI
scanner. These scanners are designed to image only the joints or the head.
During this type of scan, only the body part to be scanned is placed in
the smaller scanner while the patient lies on a couch or sits in a chair.
The images from an MRI examination are called slices, because they are
acquired in very small (millimeter-size) sections of the body. The image
slices are displayed on a computer monitor for viewing or printed as a
film. A specialist called a radiologist interprets the images produced
during the MRI examination. For emergency scans, images are interpreted
immediately so that the child can be treated quickly. For non-urgent
outpatient MRI scans, the radiologist interprets the images and sends a
report to the referring physician within a few days.
MRI is a safe procedure that does not involve radiation. However, the
magnetic field generated during an MRI examination is so strong that metal
objects or objects with metal in them, such as jewelry,
, oxygen canisters, and even wheelchairs, will be pulled toward the
machine. Therefore, MRI staff must take special precautions to ensure that
no metallic objects enter the MRI suite. MRI technologists inspect patient
clothing and accessories to make sure there are no metals on them during
—Also called anaphylactic shock; a severe allergic reaction
characterized by airway constriction, tissue swelling, and lowered blood
—An examination of the bile ducts and pancreas.
—Fear of small, enclosed spaces.
Computed tomography (CT)
—An imaging technique in which cross-sectional x rays of the body
are compiled to create a three-dimensional image of the body's
internal structures; also called computed axial tomography.
—Into a vein; a needle is inserted into a vein in the back of the
hand, inside the elbow, or some other location on the body. Fluids,
nutrients, and drugs can be injected. Commonly called IV.
—Examination of any part of the body through the use of x rays.
The process produces an image of shadows and contrasts on film.
—A medical doctor specially trained in radiology, the branch of
medicine concerned with radioactive substances and their use for the
diagnosis and treatment of disease.
No special aftercare is required following MRI scans, unless sedation or
general anesthesia was used during the scan. Then children are required to
remain in a supervised recovery area for an hour or more following the
procedure to monitor for reactions to anesthesia. If injected contrast
material is used, some minor first aid (small bandage, pain relief) for
the injection site may be necessary.
MRIs present no radiation exposure. Magnetic fields used in MRI have no
side effects for the patient. The contrast material used in MRI contains a
material called gadolinium, that is much less likely to cause severe
anaphylactic (allergic) reactions than the iodinated material used for CT
Because the MRI examination is long and the patient opening in the machine
is small, some children and adolescents may feel claustrophobic. Light
sedation or relaxants may be administered, or an MRI scanner with a more
open design may be used. For younger infants and children that require
sedation or anesthesia to complete the examination, reactions to the
anesthesia are possible, including headaches and
Younger children may be frightened of the MRI scanner, and a parent or
member may be required to be present in the scanning room. To help
alleviate fear, taking the child into the MRI room to see the equipment
prior to the procedure may be helpful. Anyone remaining in the scanning
room during the MRI examination must remove any metal objects, including
jewelry and eyeglasses.
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American College of Radiology.
1891 Preston White Dr., Reston, VA 20190. Web site:
Radiological Society of North America.
820 Jorie Blvd., Oak Brook, IL 60523–2251. Web site:
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