Introduction
The debate on the use of CT colonography (CTC) for colorectal cancer (CRC) screening has been a focus of attention for radiologists for many years, practically since the moment that this diagnostic imaging modality was first presented. Although the discussion is still open, it is necessary to distinguish the present and real role of CTC in CRC screening from another potential, ambitious role. The present role is, without any doubt, the substitution of barium enema in screening programs in cases of incomplete colonoscopy. In fact, already in 2006, the American Gastroenterological Association (AGA) endorsed CTC as the method of choice for colon investigation in these cases [ 1]. Moreover, there is strong evidence for a clear superiority of CTC over barium enema in the detection of CRC and polyps [ 2-4].
The potential role of CTC is as a first-line screening method, together with the faecal occult blood test (FOBT), sigmoidoscopy and colonoscopy. Despite the fact that CTC has been officially endorsed as a means of CRC screening in average-risk individuals by various scientific groups (namely, the American Cancer Society, the American College of Radiology, and the US Multisociety Task Force on Colorectal Cancer [ 5]), the US Preventive Services Task Force has considered the evidence insufficient to justify its use as a mass screening method [ 6]. Furthermore, Medicare currently denies reimbursement for CTC examinations performed for screening in the USA [ 7]. Nevertheless, there are both real and possible advantages for using CTC as a CRC screening test: high accuracy and examination success rate, safety, possibly greater patient acceptance and compliance, possibly advantageous cost-effectiveness, and ability to detect extracolonic pathology. There remains one important limitation to using CTC for screening, namely radiation exposure.

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