重建CT牙列图像中缺失轮廓线方法的研究

【作者】 李文玉；

【导师】 王钰；

【作者基本信息】 青岛大学 ， 计算机应用技术， 2009， 硕士

【摘要】 适于仿真需要的CT图像中牙列轮廓的快速提取,是基于CT图像的成像特点,对于成像后相邻组织间丢失的轮廓,采用相对自动的办法将其生成。本文采用Amira医学图像三维建模软件,综合分析了牙列图像的灰度范围,对牙齿各个部位的灰度取值进行了相关的实验,取得了相关数据,并对数据进行比对分析,找出了影响牙齿轮廓提取的几点原因。对于牙冠部分,由于密度高度一致造成了在CT图像中边界轮廓线的丢失,本文采用先在已提取的牙列整体连续外轮廓上,根据切矢方向的变化确定出相邻齿廓线的交汇点;再分别以两个相邻交汇点为端点,其间的轮廓点为型值点,构建标准B样条曲线作为部分齿廓线;其次,分别求出相邻齿廓线在交汇点处的一阶导矢,进而求出该交汇点处的平均导矢;然后,以两两相对的交汇点为端点构建Hermit样条插值曲线,该曲线即作为相邻齿间被丢失的轮廓线;最后,以同侧两个平均导矢为约束条件,已知轮廓线上的点为型值点,重新构造B-样条曲线做为新的齿廓线的方法来确定丢失的牙齿边界轮廓线,并可以保证构造出牙齿轮廓的C1连续性。同时,利用CT序列图像层间的一致连续性将上一层图像中凹点的区域映射到下层图像中,大大降低了操作的交互性,使实验结果更加精确。实例证明,本文采用的重构丢失齿廓线的方法,在仿真上能满足临床要求。更多还原

【Abstract】 Fast tooth contour extraction for CT images which suitable for simulation is basded on the feature of CT images, reconstruct the lost contour between the tissues semi-automaticly.This research, we used Amira^? three-dimension modeling software to reconstruction the tooth from CT images, analyzed the gray range of dental arch, and contrasted the data we had got, find several factors which affect the tooth contour extaction.On the crown, for reconstructing the contours, which are invisible in CT images due to high identity in the density value, between adjoining teeth, this paper gives a simple, and feasible method: First, the intersecting points, which were formed by the adjoining contours being parts of outer continuous contour extracted from a tooth-array cross-section in a CT image, were find out according to the saltation of the tangent vector directions on the points. Second, a B-spline, as the representation of a piece of outer contour, was built with two neighboring intersection-points as the end-points, and the outer-contour points as the interpolating points. Third, the one-order derivatives of two adjoining B-splines at common end-point were resolved respectively, and then a mean derivative at the point was computed. And then, cubic Hermit curves, as the replace of invisible contours between adjoining teeth, were built with a pairs of the opposite intersecting point as end-points; finally, construct a new B-spline of the teeth, to make sure C1 continuity of teeth contour. The fact of reconstructing 3D teeth based on the contours rebuilt with the method mentioned above has proven that a satisfying result was obtained.更多还原