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Information About Intravenous and Oral Contrast Used in CT

During many computed tomography examinations, patients may be asked to take a special contrast agent (orally, rectally or via injection). Intravenous, oral and rectal CT contrast are pharmaceutical agents (liquids) and are sometimes referred to as "dye". CT contrast is used to make specific organs, blood vessels and/or tissue types "stand out" with more image contrast to better show the presence of disease or injury. Thus CT contrast highlights specific areas of the resultant CT image or "dyes" it.

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.

There are four types of contrast agent used in CT:

  1. The type that is given via intravenous (through a vein) injection
  2. The type that is given orally
  3. The type that is given rectally
  4. A much less common type of contrast used in CT is inhaled as a gas and used for special lung and brain imaging. This technique (called Xenon CT) is only available at a small number of locations throughout the world and is only performed for rare cases.

CT Contrast Given Via Intravenous Injection

Intravenous contrast is used in CT to help highlight blood vessels and to enhance the tissue structure of various organs such as the brain, spine, liver and kidneys. "Intravenous" means that the contrast is injected into a vein using a small needle. Some imaging exams of the abdomen and gastrointestinal system use both the intravenous iodine and orally administered barium contrast for maximum sensitivity.

The intravenous CT contrast is clear like water and has a similar consistency. It is typically packaged in glass bottle or vial. A sterile syringe is used to draw it from the bottle or a power injector is used to administer the contrast. Typically between 75 cc to 150 cc (about 2.5 oz. to 5 oz) of contrast is used depending upon the patient's age, weight, area being imaged and cardiovascular health.

How does Intravenous CT Contrast Work?

A small needle is first placed into a vein in the hand or arm by the radiologist, technologist or a nurse and held in place with tape or a strap. Once the needle is in place, the vein is flushed with saline solution. Typically the contrast is loaded into a power-assisted injector, which injects the CT contrast using tubing through the needle into the body during a specific period in the CT exam. The injection is fully under the control of the technologist or radiologist. The injector is either mounted on a small trolley or hung from a ceiling mounted suspension next to the CT scanner. The contrast may also be hand injected using a large syringe connected to the needle via tubing.

Once the iodine contrast has been injected into the blood stream, it circulates through the heart and passes into the arteries, through the body's capillaries and then into the veins and back to the heart. As CT images are being acquired, the CT's x-ray beam is attenuated (weakened) as they pass through the blood vessels and organs flush with the contrast. This causes the blood vessels and organs filled with the contrast to "enhance" and show up as white areas on the x-ray or CT images. The kidneys and liver eliminate the contrast from the blood.

What Preparation is Needed Before Receiving Intravenous Contrast?

Sometimes it is necessary to not drink anything for an hour to several hours before the exam. The preparation time varies depending on the actual exam as well as the imaging center's requirements. Always ask the staff where the exam is scheduled for exact guidelines.

Is Intravenous CT Contrast Safe?

Typically, a patient will be asked to sign an "informed consent form" prior to having an CT exam which uses iodine contrast. This form will outline the potential side effects of the iodine. Overall, iodine is safe and has been used for many years and in millions of x-ray, CT and angiogram studies without serious side effects. Iodine contrast increases the sensitivity of the CT study. Thus the benefits of using iodine contrast typically outweighs the risks.

Patients should inform the radiologist or technologist if they have a history of allergies (especially to medications, previous iodine injections, or shellfish), diabetes, asthma, a heart condition, kidney problems, or thyroid conditions. These conditions may indicate a higher risk of iodine reactions or problems with eliminating the iodine after the exam.

The most common side effect of iodine includes a warm or hot "flushed" sensation during the actual injection of the iodine and a "metallic" taste in the mouth, which usually lasts less than a minute or so. This can vary depending on the type of iodine used, the rate at which it is administered, and individual patient sensitivity. There is no treatment necessary for this sensation

Another mild reaction that can take place following the administration of iodine is itching over various parts of the body with hives (bumps on the skin). This reaction can last from several minutes to several hours after the injection. This type of reaction is usually treated with medication administered by the radiologist, nurse, technologist or other physician.

More serious reactions, although much less likely, may include breathing difficulty, swelling of the throat, or swelling of other parts of the body. These reactions can be more serious if not treated immediately.

With newer types of "non-ionic" contrast (non-ionic means that the iodine has a different chemical structure than normal iodine contrast), the risk of an allergic reaction can be even less. Patients should discuss all of their questions with the imaging staff when they arrive and make sure they read and understand the "informed consent" form before having the exam.

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.

Oral 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.

Oral contrast  is often used to enhance CT images of the abdomen and pelvis. There are two different types of substances used for oral CT contrast. The first, barium sulfate, is the most common oral contrast agent used in CT. The second type of contrast agent is sometimes used as a substitute for barium and is called Gastrografin.

Barium contrast looks like and has a similar consistency as a milk shake. It is mixed with water and depending on the brand used, may have different flavors (for example, strawberry or lemon). Gastrografin contrast is a water-based drink mixed with iodine and has a tinted yellow color. When given orally, gastrografin may taste bitter.

Patients usually need to drink at least 1000 to 1500 cc (about three to four 12 oz. drinks) to sufficiently fill the stomach and intestines with oral contrast.