Future Developments .
Two important developments could dramatically change the future for virtual colonoscopy:
1°/ Computer Aided Diagnosis (CAD);
2°/ Laxative-free CT colonography.
With CAD the radiologist makes a diagnosis based on the findings of a software program performing automated image analysis by detecting shapes in the colon. As with mammography and detection of lung nodules CAD is particularly helpful when screening for disease with a low prevalence as is the case with colorectal cancer. CAD draws the radiologist’s attention to abnormalities or “polyp candidates” in the colon.
The radiologist has to decide which of these are true positives and which are false positives. By doing so CAD could act as a second reader or as a help to perform polyp detection after consensus reading (=double reading) and detect lesions which otherwise would have been missed by the radiologist. In that way CAD could help avoiding bad results as in the Cotton and Rockey trials. It would also consistently help the radiologist during his learning curve.
Recently, Taylor et al. ( Taylor et al. 2006) found that computer assisted reader software has a synergistic effect to the reviewer alone, and its standalone performance may exceed even that of experts.
It is generally accepted that the poor adherence of an asymptomatic patient population to undergo a full structural colonic examination is directly related to the discomfort caused by the cathartic preparation. Both radiologists and gastroenterologists admit that if ever virtual colonoscopy could be performed without cathartic cleansing, this would obviate any discussion whether virtual or optical colonoscopy should be used for screening for colorectal cancer. It would also dramatically improve the success of a colon cancer screening program. This method of performing virtual colonoscopy has successfully been adapted by Iannaccone et al.(Iannaccone et al. 2003). They examined successfully 203 patients with laxative-free CT colonography. A low residue diet was combined with fecal tagging over 2 days. They obtained very good results of polyp detection: 86 % for lesions > 6 mm (79 lesions), 95.5 % for lesions > 8 mm (45 lesions), 100 % for lesions > 1 cm (24 lesions).
Research is under way to combine laxative-free VC with CAD and with electronic cleansing. With electronic cleansing the tagged colonic contents are automatically removed from the colon using dedicated software.
If proved reliable in a large cohort of patients, these techniques would bring VC to the next level and make VC appropriate for widespread CRC screening with a high patient attendance and accurate performance for the significant lesion.
