Double-contrast barium enema 

Double-contrast barium enema (DCBE) is a form of contrast radiography, where an x-ray is done after administration of barium sulfate - a silver-white metal solution that highlights (contrasts) the surface of the intestinal mucosa. The result is an x-ray where the interior of the colon and rectum is highlighted.

The test is relatively simple and does not require sedation.

The patient lies down on a gurney, and a liquid containing barium sulfate is inserted into the rectum, to fill and distend part of the colon. The patient then moves so that the fluid circulates to fill the entire large intestine.

Through the same tube, air is then pumped to expand the colon and increase its visibility. Once the silver-white barium has adhered to the walls of the intestine, the doctor takes several images to be analyzed. 

DCEB is indicated in situations where it is not possible to perform a colonoscopy

DCEB is less invasive but also less sensitive than colonoscopy, so it is only recommended for more substantial changes (bigger than 1cm). It also requires medication to prepare the intestine.

If any change is detected, it will have to be further studied by taking a biopsy, through colonoscopy or rectosigmoidoscopy.