Imaging Insights: Intestinal Tract Contrast

“OK Doctor, I’ll have the CT Scan… But do I have to drink that nasty white stuff?”

You have seen your Gastro Health clinician, provided a history and had your physical exam. Your doctor can choose from many further investigative modalities be it laboratory, diagnostic testing, endoscopy or perhaps imaging. If the determination is made to obtain CT imaging, there’s a good chance it will be ordered with oral intestinal contrast, the white liquid a patient drinks prior to the CT exam of the abdomen and/or pelvis. Darn it, you may think! In fact, you are not alone. Patient satisfaction surveys have shown that patients undergoing CT scan imaging find the drinking of liquid contrast to be the least desirable part of the whole exam – and that means even worse than the IV puncture for venous access.

What is contrast?

Contrast means a difference. It is derived from the Latin words contra “against” and stare “to stand”. Medical imaging contrast is something that makes a part of the inside of the body stand out against other body parts. Contrast can be positive, neutral or negative. The white slightly chalky solution you may be asked to drink is an example of positive contrast. It contains a very small amount of the metallic element barium, which is inert, not radioactive, it is not absorbed and it does not cause allergies. The barium sulfate gives contrast greater density than internal body parts. Its use is generally considered standard of care for initial CT imaging of the abdomen and pelvis. Neutral contrast is almost like water and is of similar density to internal body parts. It is used for detailed imaging of the intestinal wall for an exam called CT Enterography. Negative contrast, like air or gas, has much lower density than internal body parts and is used in a specialized exam called CT Colonography.

Why is contrast necessary?

Simply put, contrast helps the radiologist to detect disease. Just as important, it helps to determine when disease is not present. The presence of contrast indicates the intestinal structures to the radiologist.  For example, the pancreas is an organ in the deep central abdomen that often has adjacent intestinal loops which can mimic pancreas disease. Contrast identifies the intestine and thus helps the radiologist to more accurately evaluate the pancreas. Peritoneal disease can be difficult to separate from intestinal loops without this solution. Contrast is particularly helpful in thin patients as they have little fat between internal abdominal structures. The gastrointestinal tract can have differing shape and appearance depending on whether it is collapsed or distended. Contrast assists imaging of the gastrointestinal tract in part by distention to provide more detailed images of the intestinal wall. Abnormalities of the intestinal wall due to infection, decreased blood supply or tumor can be better detected with this solution. This is why it is important to drink all of the provided contrast, to achieve a sufficient volume in the gastrointestinal tract and thereby a satisfactory distention.

Do I absolutely have to drink intestinal contrast? 

No, sometimes the patient does not need to drink the infamous liquid. Studies of some abdominal organs as well as some follow up exams may not require contrast. A CT scan ordered for some types of abdominal pain may not need contrast either, particularly in the urgent evaluation of pain. However, contrast is highly recommended for routine initial imaging and studies have supported the clinical utility of contrast over many years. The imaging center strives to obtain the highest quality medical images and perform a thorough exam for each patient. A complete exam with contrast done right the first time decreases the need for repeat imaging. Your Gastro Health clinician will determine whether imaging is indicated, and if so, which type of CT exam is most appropriate. Please understand that if your doctor has ordered the exam with oral contrast, it is because he or she wants the best possible diagnostic exam to further evaluate your clinical presentation. Contrast has been greatly improved and now has lemon, vanilla, berry or mocha flavoring. And remember, things could be worse; some centers advocate rectal contrast administration by way of catheter.