基于交比不变性的膝关节角度视频测量方法研究

Research on Video Measuring Method of Knee Joint Angle Based on Cross Ratio Invariability

本文提出了一种基于交比不变性实现膝关节弯曲角度动态测量的新方法。该方法首先进行视频图像处理,检测测量辅具上分布的25个圆形目标,确定它们各自几何中心的坐标位置,然后通过检测绑定在大小腿上的两个矩形目标位置,进一步计算大腿、小腿的伸展方向,最后应用射影几何中交比不变性原理,可直接实现膝关节弯曲角度的实时动态测量,整个测量过程无需对摄像机进行标定。医院实验证明,该方法测量精度能够满足临床使用的基本要求。

With an un-calibrated camera a new method is proposed in this paper to measure dynamically the bending angle of knee-joint based on cross ratio invariability. Firstly, by video image processing technique, we detected 25 circular objectives distributed in the aided measurement tool and determined their geometric centers in the video frame respectively. Then we further computed the extending direction of thigh and shank by detecting position of two rectangular targets tied on them. Finally, using of the principle of cross ratio invariability in Projection Geometry, we could realize real-time dynamic measurement of the bending angle of knee-joint based on the method. Experiments have proved that the measurement precision of the introduced approach could satisfy basic requirements of clinical applications.