A barium enema is an X-ray exam that can detect changes or abnormalities in the large intestine (colon). The procedure is also called a colon X-ray.An enema is the injection of a liquid into your rectum through a small tube. In this case, the liquid contains a metallic substance (barium) that coats the lining of the colon. Normally, an X-ray produces a poor image of soft tissues, but the barium coating results in a relatively clear silhouette of the colon.During a barium enema exam, air may be pumped into the colon. The air expands the colon and improves the quality of images. This is called an air-contrast (double-contrast) barium enema.Before a barium enema, your doctor will instruct you to completely empty your colon.