What is a CT scan?
A computerized axial tomography scan is more commonly
known by its abbreviated name, CT scan or CAT 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 CT 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 CT 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 CT scans performed?
CT 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, CT
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. CT scans are also used in
the chest to identify tumors, cysts, or infections that
may be suspected on a chest x-ray. CT scans of the
abdomen are extremely helpful in defining body organ
anatomy, including visualizing the liver, gallbladder,
pancreas, spleen, aorta, kidneys, uterus, and ovaries.
CT 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 CT scan?
A CT 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 CT 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.
Toxicity to the kidneys which can result in kidney
failure is an extremely rare complication of the
intravenous contrast used in CT 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 CT
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.
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