http://www.gastrojournal.org/article/S0016-5085(11)01368-0/f...
Tagging of colonic fluid and stool can be achieved with oral contrast agents before CT examination. Fecal and fluid tagging may permit identification of submerged polyps and reduce false-positive examinations due to residual stool. Stool tagging is generally achieved with ingestion of a barium suspension; fluid tagging is performed using an iodinated oral contrast agent. CT colonography performed without bowel purgation cleansing is a promising extension of the CT colonography technique in which small amounts of tagging agents are ingested 1 to 2 days before the examination to allow digital subtraction of labeled stool and fluid without a large volume catharsis.