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Information About Intravenous and Oral Contrast Used in CT

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: August 2010