CT scan
Introduction
A CT scan,
sometimes also called a CAT scan, takes pictures of the body and
uses a computer to put them together. CT stands for computerised
tomography and is a painless procedure. A series of X-rays are taken
of the body at slightly different angles, to produce very detailed
images of the inside of the body.
The images
produced by CT scans are called tomograms and they provide doctors
with information to help them reach a diagnosis about a variety of
conditions.
Why is it necessary?
Because of the
way CT images are produced, they have advantages over normal
X-ray
images in distinguishing between different types of soft
tissue. CT scans
can be performed on any part of the head or body and are
particularly good for:
-
internal
organs within the abdomen and chest - eg
liver,
kidneys,
pancreas, intestines,
lungs,
-
bone imaging
- for orthopaedic examinations
-
brain
imaging - eg to determine the cause of a stroke, and
-
vascular
imaging - examining
blood flow to different parts of the body.
How is it performed?
When you have a
CT scan, you will be required to lie on a motorised bed inside the
scanning machine which looks like a giant doughnut.
After each
X-ray is
completed, the bed on which you are lying is moved forward a small
distance You will be asked to lie very still while each scan is
taken to avoid blurring the images. Several scans will be carried
out and the whole procedure may last up to 30 minutes. If you feel
anxious, you may be given a sedative.
How does it work?
A CT scanner
uses a series of X-ray
beams to build up images of the body in slices. Unlike an
X-ray, which sends
one beam of radiation through the body, a CT scanner emits a
succession of narrow beams as it moves through an arc. This produces
a very detailed image that is not possible from a normal
X-ray.
The
X-ray detector
within a CT scanner can see hundreds of different levels of density,
including tissues
within solid organs such as the
liver. This
information can then be sent to a computer, which builds up a
cross-sectional image of the body and displays it on the screen.
Depending on the
part of the body being examined, a dye (contrast medium) may be used
to make some tissues
show up more clearly under
X-ray. This is
commonly used for brain
scans to help to show up any tumours. It is also used for scans of
the chest, as it enables doctors to find out whether a tumour can be
removed with surgery or not.
For scans of the
abdomen, you might be given a drink containing barium. This is known
as a ‘barium meal’, and shows up white on the scans as it moves
through the digestive tract
What is it used for?
CT scans are
commonly performed on the head and abdomen. Head scans are an
effective method of checking the head and
brain for
suspected tumours, bleeding, and
swelling of the
arteries.
They are also useful for investigating the
brain following a
stroke.
Abdominal CT
scans are used to detect tumours and to diagnose conditions in which
internal organs are enlarged or inflamed. Tears (lacerations) of the
spleen, kidneys
or liver,
such as may occur in serious road traffic accidents, can be revealed
by CT scan.CT scans may also be used for the following:
-
planning
radiotherapy
treatment regimes,
-
assessment
of vascular (blood
flow) diseases,
-
screening
for and assessing cardiac (heart)
disease,
-
assessment
of injury and disease to bones, particularly in the
spine,
-
to find out
bone density when investigating osteoporosis,
-
guiding
biopsy
procedures for taking
tissue samples.
Risks
CT scans involve
exposure to radiation in the form of X-rays. The level of radiation
used is kept to a minimum to prevent damage to body cells, and the
exposure to radiation depends on the number of images taken. CT
scans are quick and accurate, and they eliminate the need for
invasive surgery. The benefits of having a scan are thought to
outweigh any risks and it is generally considered very safe.
Pregnant women
should not have a CT scan, as there is a small risk that X-rays may
cause an abnormality to the unborn child. Be sure to tell your
doctor if you think there is a chance that you may be pregnant
before having a scan.
The contrast dye
used in CT scans often contains iodine, which can cause an
allergic reaction
in some people. You should inform the radiologist if you have had an
allergic
reaction to iodine or a contrast agent in the past, or if you have
any other allergies. Very rarely the dye may cause some
kidney damage in
people who already have
kidney problems. Nursing mothers should wait for 24
hours after contrast injection before resuming breastfeeding.
Healthcentral 2005
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