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How does oral CT Contrast Work?
Barium and gastrografin are made up of
substances which weaken (attenuate) x-rays. The oral contrast is swallowed and travels
into the stomach and then into gastrointestinal tract. During the CT exam which follows,
the CT x-ray beam is attenuated (weakened) as it passes through the organs containing the
contrast, for example, the large intestine. The organs filled with the contrast are then
"enhanced" and appear as highlighted white areas on the CT images.
What Preparation is Needed Before Taking
Oral CT Contrast?
It is important to eliminate as much
food as possible from the stomach and intestines in order to help the sensitivity of the
CT exam using oral contrast. Food and food remains can mimic disease when the oral
contrast is present. Thus a regimen of not eating and/or drinking for several hours before
the CT exam is required. The preparation time varies depending on the actual exam as well
as the imaging center's requirements. Patient preparation varies from center to center,
depending on a number of issues. Some types of oral CT contrast are taken at home well
before the CT examination.
Is Oral CT Contrast Safe?
In general, barium and gastrografin
contrast are safe and pass through the gastrointestinal tract in the same fashion as food
or drink. Minor side effects, such as constipation, may occur. Certain medical conditions
such as a perforated ulcer may indicate the use of gastrografin instead or barium. The
referring physicians and or radiologist will decide which type of contrast material is
most appropriate based on a patient's specific condition. Some people have reported
sensitivity to the flavoring substance used in oral barium contrast.
In some cases a CT can still provide
valuable information without the administration of a contrast agent, and the physician may
decide this is the best course for the patient at risk of reaction to contrast.
Rectal CT Contrast
Note: It is important that patients
consult the imaging location performing their CT exam for specific instructions to follow
when contrast will be used. The information contained herein is only a general guideline.
Rectal contrast is often used to
enhance CT images of the large intestines and other organs in the pelvis. There two types
of substances used for rectal CT contrast (barium and Gastrografin) are the same as the
type used for oral CT contrast, but with different concentrations. The first, barium
sulfate is the most common rectal contrast agent used in CT. The second type of contrast
agent is sometimes used as a substitute for barium and is called Gastrografin. It is not
uncommon to have an intravenous, rectal and/or oral contrast given for a CT exam which
involves the pelvis.
Rectal CT contrast is usually given
using an enema where a small plastic tip is inserted into the rectum while a patient lies
on their side. This tip is connected to a bag filled with the barium or gastrografin
contrast through a tube. After the tip is inserted, the patient lies flat and the
bag is raised above head level to allow the contrast to fill the lower intestines.
During this filling phase, the patient may feel mild discomfort, coolness, and generalized
fullness. It is important to relax as much as possible during this phase until the
CT scan is complete.
The rectal contrast helps to increase
the sensitivity of the CT exam by outlining not only the large intestines (colon), but
also the bladder, the uterus in female patients and other organs. After the exam is
complete, the rectal contrast will be drained and the patient may go to the bathroom.
How does Rectal CT Contrast Work?
Barium and gastrografin are made up of
substances which weaken (attenuate) x-rays. During the CT exam which follows, the CT
scanners x-ray beam is attenuated (weakened) as it passes through the organs containing
the contrast, for example, the large intestine. The organs filled with the contrast are
then "enhanced" and appear as highlighted white areas on the CT images.
What Preparation is Needed Before Taking
Rectal CT Contrast?
It is important to eliminate as much
food remains as possible from the stomach, intestines and rectum in order to help the
sensitivity of the CT exam using rectal contrast. Food and food remains can mimic disease
when the oral contrast is present. Thus a regimen of not eating and/or drinking for
several hours before the CT exam is required. In addition, for a pelvic CT exam where
rectal contrast will be used, a Fleets Enema (available from most pharmacies) may be
required to cleanse the colon the night before the exam. The preparation time varies
depending on the actual exam as well as the imaging center's requirements. Patient
preparation varies from center to center, depending on a number of issues. Always check
with the imaging center where the actual exam will take place to confirm the actual
preparation recommendations.
Is Rectal CT Contrast Safe?
In general, barium and gastrografin
contrast are safe and pass through the gastrointestinal tract in the same fashion as food
or drink. Minor side effects such as constipation may happen. Certain medical conditions
such as a perforated ulcer, or certain colon conditions may indicate the use of
gastrografin instead or barium. The referring physicians and or radiologist will decide
which type of contrast material is most appropriate based on a patient's specific
condition.
In some cases, a CT can still provide
valuable information without the administration of a contrast agent, and the physician may
decide this is the best course for the patient at risk of reaction to contrast.
Updated: June 11, 2008
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