基于简比的C臂图像标记点自动匹配方法

Automatic Matching Technology for C-arm Image Marked Points Based on Simple Ratio

针对C形臂X光机图像校正与标定过程中存在大量标记点需要自动对应问题,提出一种基于简比的标记点图像坐标与世界坐标自动对应方法。首先在自行设计的双层校准模板的底层模板上制作3个大的标记点,以在校准模板及其C臂图像上建立仿射坐标系;其次通过建立平面单应关系,将利用形态学方法提取出的校准模板的标记点图像坐标转换为仿射坐标;然后利用仿射变换共线三点简比不变性质,将图像仿射坐标归整,实现与校准模板标记点的自动对应;最后利用标记点投影性质区分上下两层标记点,并消除因投影失真产生的错误对应,从而实现标记点图像坐标与空间点坐标的自动准确对应。大量的测试试验表明,该方法稳定性好、鲁棒性强,具有实现简单、无需人工介入等优点,可应用于基于C臂X光图像的手术导航系统中。

This study is aimed to achieve the automatic correspondence of large numbers of markers between the image coordinates and world coordinates during the C-arm X-ray image correction and calibration.An automatic matching method based on simple ratio was proposed.At first,three large markers were made in the lower template of the self-designed double calibration template to establish the affine coordinate system on the calibration template and its X-ray image.Secondly,the markers＇ image coordinates were converted into affine coordinates through homography after they were extracted from X-ray images by morphology methods.Then the image affine coordinates of these markers were rounded to automatically correspond to the spatial markers according to the invariant of affine transformation.Finally,the upper layer markers were distinguished by the projection properties,and the corresponding errors were corrected meantime.Experimental results showed that the proposed method was stable and robust.Besides,it is simple to achieve and need no human intervention.The method could be applied to the surgical navigation system based on C-arm X-ray images.