- CAT scanning adds x-ray images with the aid of a computer to
generate cross-sectional views of anatomy.
- CAT scanning can identify normal and abnormal structures and
be used to guide procedures.
- CAT scanning is painless. Iodine-containing contrast material
is sometimes used in CAT scanning.
Patients with a history of allergy to iodine or contrast materials
should notify their physicians and radiology staff.
What is a CAT scan?
A computerized axial tomography scan is more commonly known by
its abbreviated name, CAT scan or CT scan. It is an x-ray procedure
which combines many x-ray images with the aid of a computer to generate
cross-sectional views and, if needed, three-dimensional images of
the internal organs and structures of the body. A CAT scan is used
to define normal and abnormal structures in the body and/or assist
in procedures by helping to accurately guide the placement of instruments
or treatments. A large donut-shaped x-ray machine takes x-ray images
at many different angles around the body. These images are processed
by a computer to produce cross-sectional pictures of the body. In
each of these pictures the body is seen as an x-ray "slice" of the
body, which is recorded on a film. This recorded image is called
a tomogram. "Computerized Axial Tomography" refers to the recorded
tomogram "sections" at different levels of the body.
Imagine the body as a loaf of bread and you are looking at one
end of the loaf. As you remove each slice of bread, you can see
the entire surface of that slice from the crust to the center. The
body is seen on CAT scan slices in a similar fashion from the skin
to the central part of the body being examined. When these levels
are further "added" together, a three-dimensional picture of an
organ or abnormal body structure can be obtained.
Why are CAT scans performed?
CAT scans are performed to analyze the internal structures of various
parts of the body. This includes the head, where traumatic injuries,
(such as blood clots or skull fractures), tumors, and infections
can be identified. In the spine, the bony structure of the vertebrae
can be accurately defined, as can the anatomy of the intervertebral
discs and spinal cord. In fact, CAT scan methods can be used to
accurately measure the density of bone in evaluating osteoporosis.
Occasionally, contrast material (an x-ray dye) is placed into the
spinal fluid to further enhance the scan and the various structural
relationships of the spine, the spinal cord, and its nerves. CAT
scans are also used in the chest to identify tumors, cysts, or infections
that may be suspected on a chest x-ray. CAT scans of the abdomen
are extremely helpful in defining body organ anatomy, including
visualizing the liver, gallbladder, pancreas, spleen, aorta, kidneys,
uterus, and ovaries. CAT scans in this area are used to verify the
presence or absence of tumors, infection, abnormal anatomy, or changes
of the body from trauma.
The technique is painless and can provide extremely accurate images
of body structures in addition to guiding the radiologist in performing
certain procedures, such as biopsies of suspected cancers, removal
of internal body fluids for various tests, and the draining of abscesses
which are deep in the body. Many of these procedures are minimally
invasive and have markedly decreased the need to perform surgery
to accomplish the same goal.
Are there risks in obtaining a CAT scan?
A CAT scan is a very low-risk procedure. The most common problem
is an adverse reaction to intravenous contrast material. Intravenous
contrast is usually an iodine-based liquid given in the vein, which
makes many organs and structures, such as the kidneys and blood
vessels much more visible on the CAT scan. There may be resulting
itching, a rash, hives, or a feeling of warmth throughout the body.
These are usually self-limiting reactions and go away rather quickly.
If needed, antihistamines can be given to help relieve the symptoms.
A more serious reaction to intravenous contrast is called an anaphylactic
reaction. When this occurs, the patient may experience severe hives
and/or extreme difficulty in breathing. This reaction is quite rare,
but is potentially life-threatening if not treated. Medications
which may include corticosteroids, antihistamines, and epinephrine
reverse this adverse reaction.
Computerized tomography is painless and fairly fast. It uses a
very sophisticated computer-operated X-ray machine which takes a
series of pictures throughout the spine and produces a three-dimensional
view of any damage that exists. Unlike an ordinary X-ray a scanner
does not just show bones but also soft tissues like muscles. A scanner
will probably help your doctor look at your vertebrae and discs
to form a diagnosis more accurately than anything else.
Toxicity to the kidneys which can result in kidney failure is an
extremely rare complication of the intravenous contrast used in
CAT scans. Diabetics, dehydrated individuals, or patients who already
have impaired kidney function are most prone to this reaction. Newer
intravenous contrast agents have been developed, such as Isovue,
which have nearly eliminated this complication.
The amount of radiation a person receives during a CAT scan is
minimal. In men and non-pregnant women, it has not been shown to
produce any adverse effects. If a woman is pregnant, there may be
a potential risk to the fetus, especially in the first trimester
of the pregnancy. If a woman is pregnant, she should inform her
doctor of her condition and discuss other potential methods of testing,
such as an ultrasound, which are not harmful to the fetus.
How does a patient prepare for CAT scanning,
and how is it performed?
In preparation for a CAT scan, patients are often asked to avoid
food, especially when contrast material is to be used. Contrast
material may be injected intravenously, or administered by mouth
or by an enema in order to increase the distinction between various
organs or areas of the body. Therefore, fluids and food may be restricted
for several hours prior to the examination. If the patient has a
history of allergy to contrast material (such as iodine), the requesting
physician and radiology staff should be notified. All metallic materials
and certain clothing around the body are removed because they can
interfere with the clarity of the images.
Patients are placed on a movable table, and the table is slipped
into the center of a large donut-shaped machine which takes the
x-ray images around the body. The actual procedure can take from
a half an hour to an hour and a half. If specific tests, biopsies,
or intervention are performed by the radiologist during CAT scanning,
additional time and monitoring may be required. It is important
during the CAT scan procedure that the patient minimize any body
movement by remaining as still and quiet as is possible. This significantly
increases the clarity of the x-ray images. The CAT scan technologist
tells the patient when to breathe or hold his/her breath during
scans of the chest and abdomen. If any problems are experienced
during the CAT scan, the technologist should be informed immediately.
The technologist directly watches the patient through an observation
window during the procedure and there is an intercom system in the
room for added patient safety.
CAT scans have vastly improved the ability of doctors to diagnose
many diseases earlier in their course and with much less risk than
previous methods. Further refinements in CAT scan technology continue
to evolve which promise even better picture quality and patient
safety. Newer CAT scans called "spiral" or "helical" CAT scans can
provide more rapid and accurate visualization of internal organs.
For example, many trauma centers are using these scans to more rapidly
diagnose internal injuries after serious body trauma.