基于霍夫变换的射波刀等中心误差胶片分析算法

Film analysis algorithm of isocenter error based on Hough transform for the CyberKnife system

目的提出一种基于霍夫变换(HT)的新算法提高射波刀自动质量保证(AQA)测试胶片影像分析的准确性与稳定性,并探讨胶片图像的扫描分辨率对测试结果的影响。方法获取9对胶片对AQA模体进行分析测试,首先利用中值滤波对灰度化后的胶片影像预处理,去除噪声干扰;再使用全局阈值对图像进行二值化分割,对分割后的图像进行边缘检测并利用HT提取胶片边缘直线,将胶片图像变换至正确位置;最后利用边缘检测和HT提取出影像中射野投影圆和钨球投影圆的圆心,通过分析同心度最终得到AQA测试的误差分析结果。结果所有样本分别使用本算法与原软件算法所得等中心误差结果差异无统计学意义(P>0.05),其标准差差异有统计学意义(P=0.027);表明本算法在保证了胶片分析准确性的同时具有更好的稳定性。两种方法均不能通过采用分辨率更高的胶片影像来提高分析结果的准确性和稳定性。结论本算法排除了胶片扫描摆位误差造成的干扰,为射波刀系统AQA工作提供了一种更稳定的途径。

Objective A new algorithm based on Hough transform(HT)was proposed to improve the accuracy and stability of the film image analysis of Automatic Quality Assurance(AQA)test,and to explore the influence of the resolution of film image on the test results.Methods Nine pairs of films were obtained for AQA modules in this study.Firstly,the median filter was used to preprocess the grayed-out film image to remove noise interference.Then,a global threshold was utilized to binarize the image.The images were edge-detected and the film edge line was extracted by Hough transform.The film image was transformed to the correct position.Finally,the edge of the field shadow circle and the shadow circle of the tungsten ball were extracted by the edge detection method and Hough transform.The radial error was finally obtained by analyzing the concentricity.Results There was no significant difference in the accuracy between the test results yielded by the HT method and the AQA software(P>0.05).The difference in the standard deviation of the test results was statistically significant(P=0.027),indicating that the algorithm increased the stability while ensuring the accuracy of film analysis.Increasing the resolution of film scanning failed to significantly improve the accuracy and stability of film analysis in both two methods.Conclusions The algorithm used in this study can eliminate the human error caused by film scanning placement while ensuring the accuracy of film analysis,providing a more stable way for the AQA test of the CyberKnife system.