Luminal contrast can be given to patients to improve the diagnostic accuracy of a CT examination. Modern scanners are much quicker and more sensitive and oral contrast is no longer routinely required. Despite this, some centers continue to use oral contrast for some examinations.
In days gone by, oral contrast was always given to patients who had a CT abdomen. The improved quality of images acquired by modern CT scanners means that additional luminal contrast is used much less frequently.
Oral or rectal contrast may be used in some situations, especially where the clinical question is about perforation or a leak following surgery. Rectal contrast in a patient who has recently had colon surgery increases the sensitivity of the test for picking up a leak.
It is important that luminal contrast medium, when used for CT, is appropriately diluted (~5-10%) as opposed to when used in fluoroscopy when neat contrast is used. Water-soluble contrast agents should be used to avoid the risk of chemical peritonitis if barium leaks into the peritoneal cavity.
In some patients, it is helpful to give a neutral contrast agent, e.g. water, to distend the bowel and make it easier to see bowel wall. This is particularly helpful if the question is about ischemia. Neutral oral agents are also used for CT enterography.