术中透视图像质量对双平面定位算法精度的影响

目的术中透视图像作为计算机辅助骨科手术(computer assisted orthopedic surgery,CAOS)系统最重要的源头数据,其质量水平对系统定位精度有显著影响。本文定量研究四种典型图像质量参数对双平面定位算法精度的影响。方法使用带有钢珠的标尺作为实验对象,用高精度数字放射平板采集高质量基准图像,通过定量化的人为干预来降低图像质量。使用降低质量后的透视图像作为算法输入,通过双平面定位算法得到靶点位置坐标,与测量得到的真值进行比较,得到定位误差数据。然后使用蒙特卡洛方法分析图像随机误差对定位算法精度的影响。结果相关性分析发现图像分辨率和图像畸变与定位误差有显著相关性,对比度和信噪比对定位误差影响不显著。蒙特卡洛分析发现,[-10,10]像素的随机图像误差,可导致(11.65±9.06)mm的定位误差。结论术中透视图像质量会显著影响空间定位精度,其中分辨率和图像畸变对定位误差有显著影响,对比度和信噪比影响相对较小。因此在保障手术精度的前提下制定合理的术中透视图像质量标准,对于提高CAOS系统定位精度有重要意义。

Influence of intraoperative fluoroscopy images' quality on the accuracy of bi-planar positioning method

Objective The qualities of intraoperative fluoroscopy images,which are the most important source data,have significant influence on the accuracy of computer assisted orthopedic surgery (CAOS) system.The sensitivity of the accuracy in four typical image quality parameters are studied based on the bi-planar positioning method.Methods Fiducial object with steel balls are used as the experiment object,and high quality reference images are acquired with high precision digital radiography device.Then the qualities of the images are quantitatively reduced by human intervention.The images with modified quality parameters are used as input data of bi-planar method to test the positioning error.Finally the Monte Carlo method is used to analyze the influence of random image error on the positioning accuracy.Results There is a significant correlation between the image resolution,distortion and positioning error,while image contrast and signal-to-noise ratio have no significant effect on positioning error.Monte Carlo analysis shows that random image error within [-10,10] pixels can lead to position error of 11.65 mm±9.06 mm.Conclusions The quality of the fluoroscopy images can significantly affect the spatial positioning accuracy,and the resolution and the image distortion have significant influence on the positioning error,while the contrast and signal-to-noise ratio are relatively small.A reasonable standard of intraoperative fluoroscopy image quality on the premise of ensuring the operational accuracy has a great significance for improving the positioning accuracy of CAOS system.