The authors evaluated a computed tomography (CT) colonographic technique with a combination of preex-amination orally ingested positive contrast material and postacquisition image processing to subtract out the ingested opacified bowel contents. With this technique, rigorous physical purging of the bowel was not necessary before structural examination of the colon. With images obtained in 20 patients, two readers were able to correctly identify the majority of polyps confirmed at colonoscopy. Their performance for detection of lesions larger than 1 cm was similar to that with conventional CT colonography.
Digital subtraction bowel cleansing is a technique that helps reduce the duress of the preexamination bowel cleansing required for conventional computed tomo-graphic (CT) colonography (1). With this technique, patients are asked to ingest small aliquots of positive contrast material starting approximately 2 days before examination. After image acquisition at CT colonography, the contrast material-opacified colon contents are subtracted from the images by using specialized software, which in theory leaves native soft-tissue elements of the bowel, such as polyps and folds, untouched. A radiologist then evaluates the modified images as a means of noninvasive screening for colon polyps.
The impetus for this combination of bowel opacification and image processing is the observation that the perceived discomfort and embarrassment associated with traditional bowel cleansing is a compliance barrier to colon cancer screening (2). Colorectal carcinoma is prevalent in the United States, and the clinical effect is modifiable with screening; therefore, methods with which to improve compliance with screening recommendations may confer a public health benefit (3-6). To address this compliance barrier, the replacement of traditional bowel cleansing with the ingestion of positive contrast material, referred to as fecal tagging, helps distinguish mucosal disease from feces (7). By subsequently removing the distracting and obscuring opacified bowel contents from the images, the additional subtraction step may facilitate two-dimensional evaluation and preserve the radiologists ability to evaluate the colon with three-dimensional endoluminal rendering, which is a useful step for assessing indeterminate mucosal features
(1).