Virtual colonoscopy: past, present,and future

Virtual colonoscopy has been thrust into theforefront of controversy [1]. The potential of this spe-cialized CT examination to detect colonic polyps andmasses—both for colorectal cancer screening and forthe evaluation of patients with incomplete colonos-copy—has captured the attention of the lay andprofessional communities [2]. Three key areas haveheld the widespread application of virtual colonos-copy at bay, however: (1) the unknown sensitivity ofthe test as applied in a mass screening program,(2) the expertise required to interpret the examination,and(3) the need for afull colon cleansingpreparation.The first two aspects are interrelated; the sensitivity ofthe test is affected by several factors, in particular, thesteep learning curve that had led researches to adviseagainst widespread colorectal cancer screeningwith virtual colonoscopy outside of academic centerswith experienced readers. The horizon of better soft-ware for interpretation and of computer-aided diag-nosis (CAD), in particular, may overcome thisobstacle. The third aspect—that of patient prepara-tion—is being solved by novel preparations that uselow-residue diets combined with positive-contrastopacification and electronic subtraction of residualstool [3,4].This article is designed to highlight issues ofimportance for radiologists who are contemplatingor who have recently started offering virtual colonos-copy as an option to their patients and referringphysicians. Once a radiologist is adequately trainedin the interpretation of virtual colonoscopy, it shouldbecome the study of choice for patients who undergoincomplete colonoscopy.Brief historical backgroundIn February 1994, Drs. Vining and Gelfand pre-sented the first virtual colonoscopy fly-through video(produced at Bowman Grey University and accom-panied by the sounds of Wagner’s ‘‘Ride of theValkyries’’) at the annual meeting of the Society ofGastrointestinal Radiologists held in Maui, HI. InJune of that year, virtual colonoscopy was the focusof the National Cancer Institute’s International Work-shop on Colorectal Cancer Screening held in Be-thesda, MD. This 3-day multidisciplinary conferencecovered all aspects of colorectal cancer research,prevention, diagnosis, and treatment; and made gas-troenterologists, oncologists, and radiologists awareof the importance and potential impact of virtualcolonoscopy on clinical practice. Later that year atthe Radiological Society of North America, thegeneral radiology community saw similarly impres-sive images presented by the research group fromStanford University. Since that time, research in thefield of virtual colonoscopy has blossomed to includeclinical trials, software development, stool opacifica-tion, electronic subtraction, MR imaging virtual colo-noscopy, optimization of CT technique, the study ofinterpretation visualization methods, radiation doseevaluation, the study of extracolonic findings, andCAD. The first commercial virtual colonoscopy prod-uct to appear on the market was the Navigator (GEMedical Systems, Milwakee, WI), introduced at theannual meeting of the Radiological Society of NorthAmerica in November 1995. Today, more than 20 vir-tual endoscopy products are available.