X射线CT系统投影旋转中心的测量

Measurement of center of rotation for projection in X-ray computed tomographic system

为了精确测量X射线CT成像系统的投影旋转中心坐标,校准投影几何坐标系,消除由其定位误差引起的CT图像伪影,在概述现有方法优缺点的基础上,分析推导了两个引理:"质点扫描一圈,其投影地址的积分为零"以及"任意两质点扫描投影正弦线的交点坐标之和为零"。依据上述引理,设定合适阈值对扫描得到的正弦图进行二值化分割;根据分割结果得到所有穿过物体射线的投影地址,计算这些投影地址的均值获得了投影旋转中心的坐标。实验结果表明,该方法能够高精度地测量投影旋转中心,有效地提高旋转中心校正后的重建图像质量,重复测量精度为0.08个像素。

To measure the coordinate of Center of Rotation（COR） for projection in an X-ray CT imaging system,calibrate the projection geometry coordinate system,and to eliminate the CT image artifacts caused by the positioning error of COR,this paper derives two lemmas based on the advantages and disadvantages of existing methods,i.e.＇A particle is scanned a circle by a CT scanner,then the integral of the particle＇s projection addresses under each projection view equals to zero＇ and ＇The sum of the crossing point coordinates of projection sine curves of random two particles equals to zero＇.According to the above lemmas,an appropriate threshold is set to segment the sinogram to a binary image,the projection addresses of the rays penetrating the object are got based on the segmentation results and then the COR coordinate for projection is obtained by calculating the mean of these projection addresses.The experimental results show that the method can measure the COR precisely and can improve the reconstructed image quality greatly.Moreover,the repeated measurement accuracy is less than 0.08 pixel.