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虚拟内窥镜中的路径提取和可见性分块绘制
其他题名Centerline Acquisition and Rendering Based on Visibility and Partition in Virtual Endoscopy
刘剑飞
学位类型工学硕士
导师张晓鹏
2003-06-14
学位授予单位中国科学院研究生院
学位授予地点中国科学院自动化研究所
学位专业模式识别与智能系统
关键词三维医学影像 虚拟内窥镜 中心路径提取 托拓组织 可见性分析 分块 虚拟漫游 3d Medical Lmaging Virtual Endoscopy Centerline Extraction Visibility Analysis Mesh Subdivision Virtual Navigation
摘要本文主要内容是虚拟内窥镜的几项关键技术研究和原型软件开发,包括中 心路径的自动提取、中心路径到器官壁的距离计算、中心路径的拓扑组织、人 体器官网格模型的可见性分析、中心路径引导下的自动漫游以及交互漫游。本 文的主要贡献可以概括为以下几点: 1. 提出了基于模板的并行细化算法。改进了传统细化算法的26个删除模板 以加快细化速度。通过调整改进后的删除模板(下称删除模板)的执行顺 序确保改进的正确性。在提取路径时,应用删除模板对分割结果进行逐层 的细化,并且记录每个删除点到边界的距离,以得到初始路径到器官壁的 距离。这样的距离不仅有利于碰撞检测,也适用于体数据的重建。 2. 提出了基于距离变换的中心线拓扑组织算法。对于基于模板的并行细化算 法得到的中心线进行距离变换建立三维空间数据场;再以各个局部距离最 大的点为初始点,通过最短路径对中心线上的点进行组织化,使中心线具 有拓扑结构:最后根据剪枝阈值来删除杂枝而得到最终的路径。拓扑组织 算法不仅消除了单纯并行细化算法所产生的中心线的杂枝,而且还可以整 理中心线的拓扑信息,使它能够指导漫游。 3. 提出了基于可见性和中心线的人体器官网格模型分块算法。考虑到肠道的 饶曲特性和气管的分叉特性,此算法参考建筑物漫游的可见性分析。首先 根据中心线的长度、含带的距离和弯曲程度用中心线的法平面对网格模型 进行预分块,使得器官网格模型由近似柱面(非分叉处)和近似柱面的交 (分叉处)组成;然后把每个预分块的所有边界线投影到中心线的某个法 平面上,用最小圆盘包围每一条边界线的投影,根据这些圆盘是否相交而 判断出这些边界线是否相互可见,进而判断邻近分块是否相互可见;最后 根据每个分块对应的中心线的长度、每个分块边界线对应中心线上的点所 含带的距离、以及相邻分块的可见性进行非分叉处的相邻预分块之间的重 复合并,使得每个分块对应的中心线的长度不要太短,而且分块的边界尽 量在含带距离的最小处。首次实现了包含分叉的器官网格模型的分块处 理,同时避免了以往基于中心线的分块算法将分块和可见性计算分开进行 所造成的分块与器官粗细无关的缺点。 4. 提供了包括自动漫游和手动漫游在内的虚拟内窥镜辅助诊断软件。视点的 方向可通过中心线上点的切向量来确定,视点的视角也可以通过中心线所 包
其他摘要This thesis mainly concentrates on some key techniques in virtual endoscopy, including centerline extraction, visibility analysis, distance between the centerline and the organ's border, and automatic & guided navigation etc. The contribution of this thesis is as follows: 1. A template based thinning algorithm was proposed in this thesis. Twenty-six improved thinning templates are designed to reduce the implementation time, and avoid hugging the corners similar as the result of distance transform. Adjust the implementation order of the thinning templates to guarantee the validity of the improvement. Then the initial centerline is obtained by applying the templates to delete the object points layer by layer. During the thinning process, the distance between the centerline and organ's border can be obtained by recording the distance of every deleted points. The distance not only contributes to the collision detection, but also can be used for volume reconstruction. 2. Based on the distance transform, the algorithm of topology reorganization was presented. The distance field can be constructed on the initial centerline. The topology of the centerline can also be reorganized by the shortest path extraction. And spurious branch can be pruned according to the threshold. Therefore, this algorithm can provide topology information as well as delete spurious branches. 3. A novel mesh partition algorithm was proposed based on the smoothed centerline and visibility analysis. Similar to visibility analysis in building rendering, it first partition the mesh model into cylinder-like blocks in non-ramification and joint cylinder-like blocks in ramification with the normal plane of the centerline based on its length, contained distance and the degree of twist. Then projecting the boundaries of each partition block onto the normal plane and delimiting each projection with a minimum disk, the visibility relationship of the boundaries can be established by determining whether the disks intersect with each other. Since those disks are the entries of the partitions, the visibility relationship between the partitions is equivalent to that between disks. The blocks are adjusted and merged by the centerline's length, the centerline's distance and the visibility in every block. Finally the border of every block is located in the position containing minimum distance. And the length of the block is not too long. The algorithm first solves mesh partition in ramification, and also avoids the drawbacks of previous centerline based partition algorithm. In previous algorithms, mesh partition and visibility analysis are separated and the resulting partitions are irrelevant with the width of the organs. 4. Automatic navigation and guided navigation are provided. The view direction is determined taking into account the tangent of the path. And the view angle can also be adjusted by distance between the centerline and the
馆藏号XWLW795
其他标识符795
语种中文
文献类型学位论文
条目标识符http://ir.ia.ac.cn/handle/173211/6806
专题毕业生_硕士学位论文
推荐引用方式
GB/T 7714
刘剑飞. 虚拟内窥镜中的路径提取和可见性分块绘制[D]. 中国科学院自动化研究所. 中国科学院研究生院,2003.
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