外固定支架模型重建软件开发与安装参数识别研究

Software Development and Pose Acquisition of the Taylor Spatial Frame

针对精准外固定支架的设计与开发,提出了交互式外固定支架三维模型的软件系统及外固定支架安装参数的识别算法,解决了传统方法中采用二维影像划线测量获取三维安装参数误差较大的问题.考虑远程化诊疗的潜在需求,软件系统采用浏览器/服务器架构构建基于WebGL三维模型渲染技术的三维交互场景.识别算法分为标记物位置拾取与外固定支架位姿识别两部分,通过区域生长算法分割模型文件,采用最小二乘法识别标记物位置,进而借助标记物与外固定支架的几何关系求解位姿参数.以外固定支架参考环与移动环中心距离为例,开展标记物识别方法与X光影像划线测量方法的实验对比研究.借助高精度测量仪器获取两环中心距离作为标准对照组,将上述两种方法的结果分别与标准对照组进行比较.基于标记物识别方法得到的两环中心距离与标准对照组的结果误差为0.043 mm,X光影像划线测量方法的误差为4.903 mm.实验结果表明,基于重建软件和标记物识别法获取外固定支架安装参数较传统X光影像划线测量方法精度高,并有效地将精度提升两个数量级,该方法可为开发精准高效可靠外固定支架系统提供技术支持.

Aiming at developing an external fixator system with high precision,a software for 3 D model rebuilding is designed and the method for obtaining 3 D mounting parameters is proposed in this paper that solves the problem of low accuracy in existing systems that apply a 2 D image from an X-ray photograph to estimate the mounting parameters.Firstly,the browser/server(B/S)architecture is adopted considering future application in long-distance treatment.On this basis,a 3 D model rendering procedure based on WebGL is established.Then,the mounting parameters can be derived by the 3 D model of the external fixator shown in the software.The model is divided into two steps,obtaining the maker position and fixator pose.The marker position is identified by a region growing algorithm on the STL file and with least square fitting.The pose of the fixator is computed by the geometry of the marker and fixator.With the fixator pose available,the mounting parameters,such as the distance between the reference and moving rings,can be easily obtained.Finally,experiments are performed to verify the method.Three groups of experiments are designed to determine the distance between rings:a reference group in which the distance is measured by a high precision measuring device,a 3 D model based group and a conventional 2 D image based group.In the reference group,200 measurements are implemented to measure the center of each ring,and the mean values adopted to construct the coordinates of the centers.The same experiments are repeated 10 times to eliminate the measuring errors.In the 3 D model based group,a CT image of the external fixator is converted to STL files and the3 D model is built in our software.The coordinates of the centers of the rings are directly obtained and the distance can be computed.In the 2 D image based group,the ellipse and lines are drawn on the 2 D image of the external fixator from the X-ray photograph,and the distance is estimated.By comparing the distances obtained by the 3 D or 2 D model with the measured distance,the error between 3 D model based method and measured reference is 0.043 mm,and is 4.903 mm for the 2 D model based.The results show that our method improves the accuracy compared to the conventional method.This study lays a solid foundation for the design of precise and reliable external fixator systems.