Harvard Men's Health Watch

Is prep-free colon screening on the horizon?

3D Virtual Colonoscopy

1 Centimeter

In this 3D reconstruction based on CT scans, or "virtual colonoscopy," a 1-centimeter polyp protrudes from the colon wall.

Image courtesy Michael Zalis, M.D.


New Harvard research offers a glimpse of a future when much of routine colorectal cancer screening will no longer require an aggressive bowel prep to clear the colon. Instead, the colon will be imaged in a CT scan and the stool removed digitally—akin to Photoshopping blemishes from a still photo.

Virtual colonoscopy, known officially as CT colonography (CTC), is already offered as a colorectal cancer screening procedure. Although CTC eliminates the need for physically inserting a 'scope into the body, in its present form it still requires a complete bowel prep. In addition, when CTC finds polyps a conventional colonoscopy is then required to remove them. Therefore, to avoid two preps, some people choose conventional optical colonoscopy.

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