Methods and systems are presented that improve a radiologist's ability to identify polyps by automatically and more accurately detecting and displaying colonic residue such as tagged or untagged stool or colonic fluid in medical images of the colorectal region. A virtual colonography imaging system obtains medical imagery of the colon. Improved computer-aided detection (CAD) algorithms identify colonic residue in the imagery by calculating feature vectors of and using statistical classification methods to classify regions of colonic residue to distinguish them from false positives.