Virtual Colonoscopy with an optical colonoscopy followup, where non-diminutive lesions (< 6mm) are not reported, has been found to be the most cost-effective and safest method for screening. See this MedGadget blog, and this abstract in Cancer for more details.
The TU Delft Visualisation Group is also actively performing research on Virtual Colonoscopy. Our current focus is on automatic polyp detection by using vector field visualisation techniques. Click here for the research project page, or read “L. Zhao, C. P. Botha, J. O. Bescos, R. Truyen, F. M. Vos, and F. H. Post, Lines of curvature for improved diagnosis in virtual colonoscopy, IEEE Transactions on Visualization and Computer Graphics, 2006″ (you can find this article on the group publications page).