A Technology Review on Virtual Colonoscopy Virtual Colonoscopy: An Alternative Approach to Examination of the Entire Colon Jerome Z. Liang Departments of Radiology, Computer Science and Biomedical Engineering State University of New York, Stony Brook, NY 11794, USA We have developed a virtual colonoscopy system aiming toward mass screening for polyps through the entire colon. This work reviews the key technical components of the system. Introduction Colorectal carcinoma is the second leading cause of cancer-related deaths among men and women in the United States, following lung cancer, with 56,000 deaths reported in 1998 and an estimated over 130,000 new cases per year [21]. Unfortunately the symptoms of colon cancer, such as anemia and change in bowel habits, are neither sensitive nor specific. Diagnosed cancers are often in the later stage of development, resulting in a high mortality incidence. Most colon cancer probably arises from polyps, which can take 5 to 15 years for malignant transformation. Recent studies have shown that screening of colonic polyps can reduce the mortality rate from the cancer. Optical colonoscopy and barium enema are the two most commonly used diagnostic procedures. Other tools include fecal occult blood testing (which detects only 30-40% of colorectal cancer and 10% of adenomas) and sigmoidoscopy (which fails to detect lesions in the proximal colon, where 40% of all cancers occurs, and misses 10-15% sigmoid colon carcinomas [5, 10, 15, 37]). While optical colonoscopy is accurate and can biopsy detected polyps, it is expensive ($1,800), invasive (requires scope insertion), uncomfortable (colon washing and sedation required), time consuming (hours), and carries a small risk of perforation and death (colonic perforation in one in 500 to 1000 cases and death in one in 2,000 to 5,000 cases [29]). It fails to demonstrate the entire colon in 10-15% of the cases and thus misses 10-20% of the lesions [10, 15]. Barium enema is less expensive ($400) and non-invasive, but it is less accurate (less than 78% sensitivity in detecting polyps of size from 5 to 20 mm diameter [28]), more time consuming, and requires a good deal of patient positioning and cooperation when X-ray radiographs of the colon are taken at various views. An accurate, cost-effective, non-invasive, comfortable procedure for mass screening of colonic polyps with a size less than 1 cm in diameter is extremely valuable, since the detection and removal of these small polyps will totally cure the patient. Since 1994, several pilot studies [16, 19, 23, 31, 34, 39] evaluating the feasibility of virtual colonoscopy as an alternative means for colon screening have motivated a great amount of research interests ranging from image formation, and segmentation, to visualization [1, 3, 10, 11, 13, 20, 22, 26, 27, 32, 33, 38]. This alternative means utilizes computer virtual-reality techniques to navigate inside the reconstructed three-dimensional (3D) colon model created from computed tomography (CT) or magnetic resonance (MR) images, looking for polyps. It starts with a bowel cleansing procedure, similar to that used in conventional optical colonoscopy, and is followed by inflating the colon with room air or CO2 gas --- if CT modality is utilized --- introduced through a rectal insert.