Each year, some 7000 people in The Netherlands are diagnosed with colon cancer, leading to a high mortality rate of 4500 patients. Pattern recognition expert Iwo Serlie from the Department of Applied Physics at the Delft University of Technology currently develops a rendering interface for simulated endoscopic visualisations in collaboration with Philips Medical Systems, responsible for the visualisation software and the University Medical Center of Amsterdam (AMC), which provides the patient data.
Conventional colonoscopy uses a flexible tube with an attached camera to enter the large intestine as to view whether a polyp is stuck to the intestinal wall, when the instrument is withdrawn from the patient's body. Since this method is rather painful, it is only applied in those cases where there is real cause for alarm. Virtual colonoscopy constitutes a more patient-friendly alternative to physical colonoscopy. Ir. Serlie described how a 3D image of the cleansed colon is acquired using spiral Computed Tomography (CT) imaging. The addition of a small amount of oxygen turns the colon less sticky and provides a clear imaging contrast between gas and tissues.
Virtual colonoscopy allows to inspect the colon backward and forward. Compared to the more conventional bi-directional fly-through method, the "unfolded cube" approach results in more time efficiency for the radiologist, greater effectiveness because the entire colon surface is visualised, and an enhanced sensitivity which enables the physician not only to spot the polyp but equally to exactly specify its characteristics. Ir. Serlie insisted on the radiologist's intuitivity and experience. The image can be manipulated such that the colon is fully unfolded which might give rise to a combination of artefacts. Diagnostic predictions therefore have to be made with utmost care by taking into account the grey values.
As Ir. Iwo Serlie explained in his lecture, one of the problems with previous Virtual Reality techniques for virtual colonoscopy was that one could not be sure that every polyp had been detected, because not all of the surface to be inspected was visible. A preliminary evaluation has been performed using the results of 20 patients. In 8 cases, at least one polyp was detected. The colon surface in the backward and forward visualisation was 94 percent whereas in the unfolded position, the visualised surface amounted to 99,5 percent. Using the current golden standard of physical colonoscopy, the radiologist in the pilot project discovered one polyp less than in the "unfolded cube" method.
New visualisation research has now demonstrated that unfolding techniques, where several connected views are shown in one image, greatly enhances the percentage of the surface which is visualised and decreases the amount of time needed to inspect a patient from about 19 minutes to only 7 minutes. Although not yet 100 percent ready for clinical use, the results look extremely promising and it is anticipated that virtual colonoscopy techniques can be used in the near future. More details relating to the "unfolded cube" method are available at the personal Web site of Ir. Iwo Serlie.