Helical CT colonography (virtual colonoscopy): the challenge that exists between advancing technology and generalizability.

Abstract

R apid volumetric helical CT has extended body CT imaging far beyond standard axial examinations. Technical improvements in high-resolution CT acquisition, coupled with advanced three-dimensional (3D) computer graphics, have permitted interactive 3D visualization in medical imaging [1-3]. “Helical CT colonography” broadly refers to acquisition of planar helical CT images, with interactive display using a variety of two-dimensional (2D) and 3D visualization techniques to evaluate the colonic mucosa for colorectal polyps [4-8]. “Virtual colonoscopy” refers to computersimulated 3D endoscopic visualization of the colonic mucosal surface. This rapidly growing field has gained multidisciplinary attention as a potential noninvasive test for colorectal polyps and cancer, with the hope that compliance will be increased, costs reduced, and diagnostic performance enhanced compared with current practice. Although marked technologic advancements have been achieved, the challenges that lie ahead include standardization, validation, and implementation of these techniques in generalized settings. We review the current status of and future developments in image acquisition, image display, and clinical validation. Colonic carcinoma remains the second leading cause ofcancerdeath in the United States [9]. Approximately 155,000 new cases of colorectal cancer are diagnosed annually in the United States, and each year an estimated 60,000 patients die of their disease. The total cost of colorectal cancer annually in the United States is estimated to be $10 billion, of which $2.5 billion represents direct medical costs [10]. Adenomatous polyps are widely held to be precursors of colorectal cancer [1 1]. An estimated 30-50% of the 60 million Americans more than 50 years old have one or more adenomatous polyps [12-14]. Clinical practice standards support the removal of polyps larger than 1 cm [15]; approximately 10% ofpatients who undergo a baseline colonoscopy are predicted to have polyps ofthis size [16, 17]. Such polyps may be best detected with penodic colonoscopic surveillance, which has important financial consequences. Ransohoff and Lang [18] predicted that ifthe more than 20 talllion Americans older than 50 years with an adenomatous polyp have colonoscopic surveillance every 3 years, more than 7 million colonoscopies would be performed each year at a cost of roughly $3.5 billion. Although providing a means for diagnostic screening and therapeutic intervention for colonic polyps, colonoscopy is expensive and invasive and most average-risk patients have negative findings. Helical CT colonography may offer a more rapid and less morbid alternative to colonoscopy.