Virtual Endoscopy Study

Virtual Endoscopy (VE) is an application of Virtual Reality in modern medicine. It is a technique incorporating the research about Computer Graphics, Image Processing, Scientific Computing Visualization, Virtual Reality, etc. VE simulates optics endoscopy by use of medicine images. With the advent of high resolution medical images (such as CT, MR I etc. )and the progress of Virtual Reality technique , VE is developing rapidly . It has been one of the most flourished fields during the application of VR to practice. The aim of VE system research is to provide trusty means for medical diagnoses, and to spread the application to the fields such as assistant diagnoses, surgery planning and training. VE is a non-touched medical diagnoses method and is becoming more and more widely used in many medical fields since it avoids the risk of invading body when the actual optical endoscopy is used. Some key techniques and realizations of VE are systematically investigated in this dissertation.Firstly, the medical image of DICOM is analyzed. DICOM file format is widely applied in CT, MRI and PACS systems. When DICOM files is read correctly, the information needed for 3D reconstruction, such as the patient's part examined, the window width, the window center and the slice thickness of the image and so on, will be extracted. Then, some kind of 3D reconstruction based on surface rendering algorithms are introduced, and the realization process of Marching Cube algorithm is addressed briefly.Secondly, an interactive and semi-automatic image segment method, named curved-cutting, is designed in this system. It is necessary to cut off part of tissues when the interested region is hided as a 3D object is displayed. In our system, it is enough when the user draw a closed curve by moving the mouse. It is very time-consuming to judge the projectionof every voxel is in or out of the curve directly. So a fast method based on region-growing is put forward and realized. And besides ,the segment operation of undo/redo is realized without extra memory.Thirdly, the process and method of the realization of fly-through are discussed in detail. The key step of getting the hollow tissue's center path , also named skeletonization , is another time-consuming work. Then one of the skeletonization algorithms available is analyzed and improved.Finally, practical path-smoothing algorithm based on NURBS is given since image jumping often occurs when flying along the result of skeletonization. Furthermore, with the representation of homogeneous coordinates, the shape modification based on weight is discussed from the point of geometry. Physical meaning of weight is uncovered and then theoretic evidence is provided to modify curve shape by using weight effectively.