Real-time surface analysis and tagged material cleansing for virtual colonoscopy

Virtual Colonoscopy is an important procedure for screening and detecting colorectal cancer. It increases patient comfort and reduces risks compared to optical colonoscopy. Oral contrast is used to emphasize the soft tissue border and avoid the need for physical colon cleansing. In order to ensure a reliable diagnosis, it is currently necessary to remove the fecal tagging in a time consuming pre-processing step. As the result can include artifacts and may effect polyp size, this paper proposes a novel technique that allows realistic visualization of the surface boundary based on unmodified CT images. A combined iso-surface reconstruction and direct volume rendering approach is developed to handle partial volume artifacts efficiently and allow on-the-fly surface reconstruction. The algorithm supports real-time analysis of detected surfaces and can differentiate material transitions between air, soft tissue and fluid. The surface-based rendering furthermore allows photo-realistic visualization through screen space shading to support procedure planning and interactive training.