Upper gastrointestinal series tract in addition to barium, and this procedure is called double-contrast imaging. In this case the gas is referred to as the negative contrast medium. Traditionally the images produced with barium contrast are made with plain-film radiography, but computed tomography is also used in combination with barium contrast, in which case the procedure is called CT enterography. Various types of barium X-ray examinations are used to examine different parts of the gastrointestinal tract. These include barium swallow, barium meal, barium follow-through, and barium enema. The barium swallow, barium meal, and barium follow-through are together also called an upper gastrointestinal series
Lower gastrointestinal series colon to distend it and provide better images (often called a "double-contrast" exam). If air is used, the enema tube will be reinserted if it had been removed and a small amount of air will be introduced into the colon, and more X-ray pictures are taken. The patient is usually asked to move to different positions and the table is slightly tipped to get different views. If there is a suspected bowel perforation, a water-soluble contrast agent is used instead of barium. The procedure is otherwise very similar, although the images will be of poorer quality. If a perforation exists,