How
should I prepare for my CT procedure?
How should I prepare for my CT procedure?
Depending on the part of the body to be examined,
you may be asked to take only clear liquids by mouth before CTA. You may
be asked whether you have asthma or any allergies to foods or drugs, and
what medications you are currently taking. If you are pregnant, you should
inform the technologist before the procedure. You probably will not have
to undress if you are undergoing an exam of the head, neck, arms or legs
but you will have to remove any jewelry, hair clips, dentures and the like
that could show up on the x-rays and make them hard to interpret.
What does the equipment look like?
DependingA CT scanner is a specialized x-ray machine
that looks like a large square doughnut. It has an opening measuring about
two feet in diameter that surrounds a narrow table. Inside the frame of
the scanner is a rotating device with an x-ray tube mounted on one side
and a banana-shaped detector opposite it. Nearly all CTA studies use an
advanced type of unit called a spiral CT machine that looks like any other
type of CT unit, but is able to record a large number of pictures in a short
time. This means that patients do not have to hold their breath for a prolonged
period.
An example of the CT equipment that may be used is
shown to th right.
How is the procedure performed?
Most of the time for a CTA examination is spent
setting everything up. Actually recording the images takes only seconds.
After changing into a hospital gown and having an IV set up, you will answer
questions about things that might complicate the exam (such as allergies),
and then you will lie down on a narrow table. The part of your body to be
examined will be placed inside the opening of the CT unit with the aid of
criss-crossed positioning lights. A test image is taken to determine the
best position, and a small dose of contrast material may be given to see
how long it takes to reach the area under study. Then the IV is hooked up
to an automatic injector, contrast material is injected, and the scan begins.
Afterward, the images will be reviewed and, if necessary, some will be repeated.
How does the procedure work?
Before the actual exam begins, you will have a dose
of contrast material injected into a vein to make the blood vessels stand
out. An automatic injector machine is used that controls the timing and
rate of injection, which may continue during part of the time images are
recorded. During the examination, the rotating device spins around the patient,
creating a fan-shaped beam of x-rays, and the detector takes snapshots of
the beam after it passes through the patient. As many as one thousand of
these pictures may be recorded in one turn of the detector. The real work
of CTA comes after the images are acquired, when powerful computer programs
process the images and make it possible to display them in different ways,
for instance, in cross-sectional slices or as three-dimensional "casts"
of the blood vessels.
What will I experience during the procedure?
CTA takes about 10 to 25 minutes from the time the actual examination begins.
Overall, you can expect to be in or near the examining room for 20 to 60
minutes. You may feel warm all over when contrast material is injected,
but you should not feel pain at any time. Any CT study requires that you
remain still during the exam. Pillows and foam pads may help make it more
comfortable. At the same time, the nurse or technologist may use pads or
Velcro straps to keep an area of your body from moving. The examination
table will move into and out of the scanner opening, but it is not enclosed,
and only a small part of your body will be inside at any one time. You may
be asked to hold your breath for 10 to 25 seconds to be sure that the images
will not be blurred. During the time that no actual imaging is taking place,
you are free to ask questions or talk to the technologist, but friends or
relatives will not be allowed in the examining room. Once the needed images
have been recorded, you will be free to leave. You can eat immediately,
and it is a good idea to drink plenty of fluids in the hours after the exam
to help flush contrast material out of the system.
Who interprets the results and how do I get them?
A radiologist, who is a physician experienced
in CTA and other radiology examinations, will analyze the images and send
a report to your personal physician, who in turn will discuss the findings
with you. Typically the results of CTA are available within 24 hours, although
in complicated cases special computer analysis may take somewhat longer.
What are the benefits vs. risks?
Benefits
- CTA can be used to examine blood vessels in
many key areas of the body, including the brain, kidneys, pelvis, and
the lungs. The procedure is able to detect narrowing of blood vessels
in time for corrective therapy to be done.
- This method displays the anatomical detail of
blood vessels more precisely than magnetic resonance imaging (MRI) or
ultrasound. Today, many patients can undergo CTA in place of a conventional
catheter angiogram.
- CTA is a useful way of screening for arterial
disease because it is safer and much less time-consuming than catheter
angiography and is a cost-effective procedure. There is also less discomfort
because contrast material is injected into an arm vein rather than into
a large artery in the groin.
Risks
- There is a risk of an allergic reaction—which
may be serious—whenever contrast material containing iodine is injected.
If you have a history of allergy to x-ray dye, your radiologist may advise
that you take special medication for 24 hours before CTA to lessen the
risk of allergic reaction. Another option is to undergo a different exam
that does not call for contrast material injection.
- CTA should be avoided in patients with kidney
disease or severe diabetes, because x-ray contrast material can further
harm kidney function.
- If a large amount of x-ray contrast material
leaks out under the skin where the IV is placed, skin damage can result.
If you feel any pain in this area during contrast material injection,
you should immediately inform the technologist.
- If you are breastfeeding at the time of the
exam, you should ask your radiologist how to proceed. It may help to pump
breast milk ahead of time and keep it on hand for use after CTA contrast
material has cleared from your body.
- Women should always inform their doctor or x-ray
technologist if there is any possibility that they are pregnant. See the
Safety page for more information about pregnancy and x-rays.
