Introduction

Computed tomographic colonography (CTC), commonly known as Virtual Colonoscopy (VC) has recently emerged as a fundamentally new technique for radiologic imaging of the colon with the unique potential for broad application in population screening for colorectal cancer. Yet, when framed in the philosophic question of "why do we do CTC?", the analogy to Mt. Everest becomes clear. We do CTC because the technology exists.

In the early 1990s, the introduction of spiral CT scanners, and powerful new computer workstations for image processing prompted individual pioneers to exploit the new technology at least in part, because they could. Coin obtained a United States patent for CT reconstruction of the colon (Coin et al. 1995), while Vining is credited with the first clinical demonstration of what he termed 'virtual colonoscopy' (Vining and GElfand 1994). Hara at the Mayo Clinic (Hara et al. 1996) and Royster at Boston University (Royster et al. 1997) confirmed clinical feasibility for polyp detection. Fenlon then showed

Chair Emeritus and Professor of Radiology, Boston University School of Medicine, Boston Medical Center, 88 East Newton Street, Boston, MA 02118

that the sensitivity of CTC equaled that of conventional colonoscopy for detection of large polyps and cancers in a landmark 100 patient Boston University study published in the New England Journal of Medicine (Fenlon et al. 1999). As they say, the rest is history.

As CTC enters its second decade, it is no longer new, but retains many compelling features. Technologically it maintains its sophisticated, innovative appeal and still exhibits great potential to evolve further. Scientifically, CTC is reframing strategies for colorectal cancer screening and now challenges the primacy of colonoscopy and the specialty of gas-troenterology for the diagnosis of colon disorders. At the same time, CTC has been a dominant focus of research in abdominal and gastrointestinal radiology for several years, stimulating an enormous volume of original scientific investigation as well as media and industry attention. Impressive clinical results continue to appear from investigators throughout the world, including North America, Europe, and Australia (Yee et al. 2001; Macari et al. 2002; IannaconE et al. 2003; Edwards et al. 2004). Even more important is the totally non-invasive aspect of CTC (no drugs, no contrast media and no injections) which has won the favor of many physicians and their patients, especially when compared to optical colonoscopy. In preference studies comparing the two tests, patients usually prefer CTC despite the unavoidable biases of pre-endoscopy sedation (SvEnsson 2002). It is this patient friendly, 'compliance enhancer' nature of CTC which has been able to attract otherwise reluctant patients to undergo colorectal cancer screening. A recent U.S. hospital think tank reported that some 60% of patients having virtual colonoscopy had never had any prior form of colorectal cancer screening (Advisory Board 2004) (Fig. 1). In the United States, several HMOs have begun to reimburse for colorectal cancer screening using CTC, and wider reimbursement coverage is expected in 2006 which should lead to rapid wide dissemination into clinical practice.

VC patients: prior experience with CRC Screening Compliance enhancer

VC patients: prior experience with CRC Screening Compliance enhancer

No Yes

The Advisory Board - Washington, DC June 2004

Fig. 1. CTC as a 'compliance enhancer'. Pie chart from a US hospital think tank study showing that among patients having virtual colonoscopy 60% had never had any prior colon cancer screening

No Yes

The Advisory Board - Washington, DC June 2004

Fig. 1. CTC as a 'compliance enhancer'. Pie chart from a US hospital think tank study showing that among patients having virtual colonoscopy 60% had never had any prior colon cancer screening

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