Virtual Colon Flattening
We present a new method to visualize virtual endoscopic views. We propose to flatten the organ by the direct projection of the surface onto a set of cylinders. Two sampling strategies are presented and the introduced distortions are studied. A non-photore
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Abstract. We present a new method to visualize virtual endoscopic views. We propose to flatten the organ by the direct projection of the surface onto a set of cylinders. Two sampling strategies are presented and the introduced distortions are studied. A non-photorealistic technique is presented to enhance the perception of the images. Finally, an approximate but real-time endoscopic fly-through is possible by using the data obtained by the projection technique.
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Introduction
Virtual endoscopy deals with the inspection of hollow organs and anatomical cavities using medical imaging (e.g. CT and MRI) and computer visualization techniques. Virtual endoscopy has the potential of becoming a substitute of real endoscopy for some diagnostic procedures. A real endoscopy is invasive and, furthermore, involves a certain degree of risk for the patient. Most of the virtual endoscopy techniques presented in the last years [1-3] concentrate on simulating the view of a real endoscope. This is the view that the endoscopists are used to. It can be useful for certain applications, like in an intraoperative scenario, but it is not necessarily the best way to inspect the inner surface of an organ. Actually, a real endoscope and organ are subject to physical limitations that a virtual endoscope and organ do not have. This paper considers virtual colonoscopy, which focuses on the examination of the colon. Physicians are mainly interested in visualizing the inner surface of the colon which is where polyps can be detected with endoscopy. It is important that the physician can estimate the size of polyps, since large polyps are more likely to develop into malignities. The usual endoscopic view visualizes just a small part of the surface. Furthermore, it is difficult to detect polyps that are situated behind the folds of the colon. An efficient way to inspect the inner surface would be to open and flatten the colon and then examine its internal surface. Unfortunately, this cannot be done in reality if we want that the patient survives. On the other hand, there is no patient damage if this dissection of the organ can be achieved virtually with the medical data obtained by CT or MRI (i.e. the virtual organ). Some authors proposed a technique to straighten and unravel an organ virtually [4][5]. Their approach starts with defining a path which is placed as close to D. S. Ebert et al. (eds.), Data Visualization 2001 © Springer-Verlag/Wien 2001
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the center of the object as possible. -Then a sequence of frames is calculated. For each frame, a cross-section orthogonal to the path tangent is calculated. Then the central path is straightened and the cross-sections are piled to form a stack. As a last step the straightened colon is flattened obtaining a volume model of the flattened colon. The model is displayed afterwards using standard volume rendering techniques. This method allows to visualize the complete surface at once. One of the main problems of this technique appears in high curvature areas of the central path, i.e. at path locat
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