Computed tomography (CT), formerly referred to as computerized axial
tomography (CAT), is a common diagnostic imaging procedure that uses
to generate images (slices) of the anatomy.
Computed tomography (CT) is an x-ray imaging procedure used for a variety
of clinical applications. CT is used for spine and head imaging,
gastrointestinal imaging, vascular imaging (e.g., detection of blood
staging and radiotherapy treatment planning, screening for cancers and
heart disease, rapid imaging of trauma, imaging of musculoskeletal
disorders, detection of signs of infectious disease, and guidance of
certain interventional procedures (e.g., biopsies). CT is the preferred
imaging exam for diagnosing several types of cancers, and along with the
chest x ray, CT is the most commonly performed procedure for imaging the
chest. CT is also used to perform noninvasive angiographic imaging to
assess the large blood vessels.
CT may be performed on newborns, infants, children, and adolescents. In
children, CT is most frequently used in the hospital emergency department
to evaluate the effects of trauma, especially to the head, face, brain,
and spine, and to diagnose or rule out
and other abdominal disorders because a scan can be completed in less
than 20 seconds. Chest CT examinations are used to assess complications
from infectious diseases, such as
, inflammation of the airways, and birth defects. CT scans of the pelvic
area are used to image ovarian cysts and tumors, bladder abnormalities,
urinary tract stones, kidney disease, and bone disease. Head CT scans are
used to examine the brain and sinuses. For children with cancer, CT is
used to assist in treatment planning and to monitor cancer progression and
response to treatment. For children requiring complex surgeries (e.g.,
brain, spine), CT is often used to produce images of the anatomy that help
surgeons plan the surgery. Newer CT scanners, called multislice or
multidetector CT, are used to rapidly image newborns to assess congenital
CT is performed using a specialized scanner, an x-ray system, a patient
table, and a computer workstation. The CT scanner is shaped like a large
square with a hole in the center or round like a doughnut. X rays are
produced in the form of a beam that rotates around the patient. During a
CT scan, the patient table is moved through the center hole as x-ray beams
pass through the patient's body. The x rays are converted into a
series of black-and-white images, each of which represents a
"slice" of the anatomy.
CT scans are conducted by a technologist with specialized training in x
rays and CT imaging. During scanning, the technologist operates the CT
scanner using a computer located in an adjacent room. Because movement
during the scan can cause inaccurate images, the technologist instructs
the patient via an intercom system to hold their breath and not move
during the x rays. The scan itself may only take five to 15 minutes, but
total examination time may be up to 30 minutes, since the patient must be
prepped and positioned. Abdominal CT scans usually require that the child
drink a solution that contains a dye, called oral contrast, that shows up
on the CT images to help better define internal organs. For pelvic scans,
contrast material may be delivered via the rectum. Some CT scans also
require the injection of contrast material into the vein to help define
the blood vessels and surrounding tissue.
The images from CT 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
radiologist interprets the x-ray images produced during the CT
examination. For emergency CT scans, images are interpreted immediately so
that the child can be treated as soon as possible. For non-urgent
outpatient CT scans, the radiologist interprets the images and sends a
report to the referring physician within a few days.
For emergency situations, CT scans are performed in a hospital radiology
department in conjunction with
False color computed tomography scan through the abdomen, showing
the liver (larger yellow organ) and spleen (smaller yellow organ).
The abdominal aorta is colored red and located above the spine and
between the kidneys.
(Photo Researchers, Inc.)
the emergency department. For non-urgent conditions, CT scans can be
performed on an outpatient basis in a hospital radiology department or
outpatient imaging center. In small hospitals or hospitals in rural areas,
a CT scanner may not be permanently located in the hospital; rather, a
mobile imaging service will be contracted to bring a specially designed
trailer with CT equipment to the hospital on prescheduled days.
CT scans expose the child to radiation, and overuse of CT scanning has
received attention from organizations that regulate medical radiation
exposure. Although no side effects have been linked to radiation exposure
from CT imaging, the Food and Drug Administration has issued guidance to
physicians regarding levels of radiation during pediatric CT examinations.
New CT scanners have preset imaging features that allow scanning at the
lowest radiation dose for the child's weight and age.
Oral contrast may be unpleasant tasting, although chocolate, vanilla, and
fruit flavors may be available. Injected contrast can cause sensations of
heat or cold through the body. Some children may have allergic reactions
to the contrast material, although severe reactions are rare. Parents
should inform CT staff if their child has ever had a reaction to any
medication, contrast material, or anesthesia. Because contrast material
may contain iodine, sensitivity to contrast material may occur if the
child has other
to iodine or seafood, and CT staff should be informed if the child has
such allergies. Also, because CT contrast material can affect kidney
function, parents should notify CT staff if their child has kidney
Abdominal CT examinations usually require fasting for at least 12 hours
before the scan. If the intestines will also be imaged, a laxative before
the scan is required. Parents should alert CT staff if children are
diabetic and taking insulin, since
can occur with missed meals.
Before the CT scan, the patient has to change into a hospital gown. When
oral contrast is necessary, patients need to arrive at least one hour
before the scan to drink the contrast solution. During the scan, the child
is asked to lie on the CT table. Positioning devices, such as head cradles
or knee rests, may be used. For very young or very active children, foam
or Velcro restraints may be used to minimize movement during imaging. Or
sedation may be used if children cannot remain still. After positioning
the child, the technologist inserts an intravenous catheter to inject
CT scanners may frighten young children, so prior to the imaging
examination, the basic procedure should be explained to help reduce
. Some radiology departments offer special patient education booklets for
children that help explain imaging procedures.
No special aftercare is required following CT scans, unless sedation or
general anesthesia was used during the scan. In these cases, children are
required to remain in a supervised recovery area for an hour or more
following the procedure to be monitored for reactions to anesthesia. If
injected contrast material is used, some minor first aid (small bandage,
relief) for the injection site may be necessary.
Radiation exposure is a risk during CT examinations. However, the
radiation from a CT scan is usually less than that from regular x rays,
and the benefits of the examination far outweigh the minor radiation dose
received during the scan.
Some children may have reactions to anesthesia or sedation, including
headaches, shivering, or
. Rarely, severe anaphylactic reactions can occur that require emergency
—Also called anaphylactic shock; a severe allergic reaction
characterized by airway constriction, tissue swelling, and lowered blood
—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.
Margolis, Simeon, et al.
The Johns Hopkins Consumer Guide to Medical Tests: What You Can Expect,
How You Should Prepare, What Your Results Mean.
New York: Rebus Inc., 2002.
Medical Tests: A Practical Guide to Common Tests.
Boston, MA: Harvard Health Publications, 2004.
Segen, J. C., et al.
The Patient's Guide to Medical Tests: Everything You Need to Know
about the Tests Your Doctor Prescribes.
New York: Facts on File, 2002.
Shannon, Joyce Brennfleck.
Medical Tests Sourcebook: Basic Consumer Health Information about
Detroit, MI: Omnigraphics, 2004.
Harvey, D. "Evaluating Pediatric Trauma: Imaging vs. Lab
5 (August 2, 2004): 14–16.
American College of Emergency Physicians.
2121 K St., NW, Suite 325, Washington, DC 20037. Web site:
American College of Radiology.
1891 Preston White Dr., Reston, VA 20191. Web site:
Radiological Society of North America.
820 Jorie Blvd., Oak Brook, IL 60523–2251. Web site:
, November 1, 2004. Available online at
December 21, 2004).
"Pediatric CT (Computerized Tomography)."
Radiology Info: The Radiology Information Source for Patients.
Available online at
(accessed December 21, 2004).