利用EPID图像金球位置自动跟踪算法研究

Study on Automatically Detecting the Golden Marker's Position by Using EPID Images

目的:建立一种全新的算法,并利用EPID(Electronic Portal Imaging Device)图像实时读取预埋于体内金球的投影位置,自动重建金球在体内的投影位置坐标。方法:利用所编算法和Matlab软件进行EPID图像读取和处理金球投影位置并自动重建金球在体内的位置坐标。即取通过图像处理和圆曲率识别各自获得的金球投影位置坐标集合的交集为真实的2D坐标,并依此反推到病人体内获得金球位于靶区当中真实的3D重建坐标。结果:本研究共进行了三组实验,每组为两个交角拍摄的EPID片。每组所有EPID片上的金球投影位置探测成功率分别为94.44%,93.75%,94.44%。算法重建的和利用CT扫描在TPS中重建的金球位置的三维坐标最大偏差为2.2 mm,最小偏差为0.1 mm。该算法于所使用的PC上完成一组(两张交角EPID图像)图像处理和重建的运行时间<1s。结论:对于多组相交角度拍摄的含金球投影位置的EPID图像,所编算法金球探测成功率比较高,平均为94%,算法重建出的靶区周围金球三维坐标同CT扫描重建出的坐标相比较,偏差在可以接受的范围内。但是该程序参数调节较复杂,而且EPID板接缝处剂量会影响探测成功率,还需要进一步开发自动参数计算程序和消除EPID板接缝处剂量影响。

Abstract：Objective： To study a new algorithm and read out the projected positions of the gold markers pre-implanted in the patient＇ s body on EPID images and reconstruct automatically the coordinates of the gold markers in the patient＇ s body on real time bases. Methods： Read the EPID images, figure out the projected positions of the gold markers and reconstruct the coordinates of that in the body by using the new algorithm and matlab. That is getting the intersection of the two groups of coordinate＇ s set acquired from image processing and recognition of circle curvature respectively, then get the real 3D coordinates of all the gold markers in the target in the patient＇ s body. Results： A total of three sets in our study have been done, and the detection success rates of the projected position coordinates of the gold markers coming from all angled EPID images in each set are 94.44%, 93.75%, 94.44% respectively. The maximum deviation between the coordinates of gold markers positions reconstructed by this algorithm and ones reconstructed by TPS is 2.2 mm with aminimum of 0.1 mm. The total running time of Im- age processing and the reconstructionalgorithm which contains dealing with a group of two angled EPID images is less than ls in the PC used for this study. Conclusions： For the EPID images from multiple gantry angles which contain gold marker＇s projected positions,the detection success rate of reading the projected positions of gold markers is relatively high, with an average of 94%. The difference between coordinates of gold markers positions reconstructed by the algorithm and ones recon-structed by TPS is in the acceptable range. But it＇ s complicated to adjust the parameters in our program as there are too many parameters and the dose which comes from the edge joints of EPID boards can affect the detection success rates. In order to deal with these two problems we have to develop new programs which can calculate the parameters automatically and quicklyand eliminate the influence of the dose which comes from the joints of EPID boards