Computed Tomography
(CT Scan) for Back Problems
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What is the
test?
CT scans are pictures taken by a specialized
x-ray machine. The machine circles your body
and scans an area from every angle within that
circle. The machine measures how much the x-ray
beams change as they pass through your body.
It then relays that information to a computer,
which generates a collection of black-and-white
pictures, each showing a slightly different
“slice” or cross-section of your
internal organs. Because these “slices” are
spaced only about a quarter-inch apart, they
give a very good representation of your internal
organs and other structures. Doctors use CT scans
to evaluate all major parts of the body, including
the abdomen, back, chest, and head.
A CT scan is not a very common test to have
done for back problems. It does a better job
showing the abdominal internal organs than showing
details of the bones in the spine. But some back
pain is caused by problems in these internal
organs, such as the pancreas or the kidney. The
CT scan is an excellent way to examine these
organs. Also, the CT scan can be combined with
a test called a "myelogram" (discussed
separately) to give a clear view of the spinal
cord and places where the vertebral bones might
be pinching it.
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How
do I prepare for the test?
If you are having an abdominal CT scan, you
might have to fast 2–4 hours before your
test. You also may have to drink a large quantity
of oral contrast, a fluid that will show up on
the CT scan and help define the lining of some
internal organs. Tell your doctor if you’re
allergic to x-ray contrast dyes, may be pregnant,
or have diabetes and take insulin. Insulin can
cause hypoglycemia after missing a meal.
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What
happens when the test is performed?
The test is done in the radiology department
of a hospital or in a diagnostic clinic. You
wear a hospital gown and lie on your back on
a table that can slide back and forth through
the donut-shaped CT machine. A technician or
other health care professional inserts an IV
and injects more contrast dye through it. This
dye outlines blood vessels and soft tissue to
help them show up clearly on the pictures.
The technologist moves the table with a remote
control to enable the CT machine to scan your
body from all of the desired angles. You will
be asked to hold your breath for a few seconds
each time a new level is scanned. The technologist
usually works the controls from an adjoining
room, watching through a window and sometimes
speaking to you through a microphone. A CT scan
takes about 30–45 minutes. Although it’s
not painful, you might find it uncomfortable
if you don’t like to lie still for extended
periods.
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What
risks are there from the test?
There are a few small risks. The contrast dye
used in the test can damage your kidneys, especially
if they are already impaired by disease.However,
some newer dyes are less likely to cause kidney
injuries. If kidney damage does occur, this is
usually temporary, although in some rare cases
it becomes permanent. If you are allergic to
the dye used in the procedure, you may get a
rash or your blood pressure may drop enough to
make you feel faint until you get treatment.
As with x-rays, there is a small exposure to
radiation. The amount of radiation from a CT
scan is greater than that from regular x-rays,
but it’s still too small to be likely to
cause harm unless you’re pregnant.
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Must
I do anything special after the test is over?
No.
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How
long is it before the result of the test is
known?
The radiologist can probably give you preliminary
results within a day. The formal reading of your
CT scan might take another day.
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