Barium sulphate is radiopaque, meaning that X-rays do not readily pass through it. It is also not easily absorbed by the body. As a result of these two qualities, barium sulphate can be used to obtain X-ray or CT scan images of the soft tissues of the digestive tract, which normally would be nearly invisible on an X-ray.
Barium sulphate comes as a powder that can be mixed into a thick drink for use in upper GI (gastrointestinal) studies. The patient has to drink the barium sulphate "shake", and then the stomach, and later on the small intestine, can be seen radiographically. The time that it takes for the shake to move through the system can be studied, and any blockages, leaks, or other gross abnormalities can be detected.
For lower GI studies, the barium sulphate is sometimes mixed into an enema preparation instead. This is used to study the colon and the large intestine to check for abnormal growths, leakage, or small pockets known as diverticula.