CT图像重建中旋转轴的不稳定对图像质量的影响

Effects on spatial resolution of CT image caused by nonstationary axis

为了研究大型工业计算机断层成像 (CT)系统中由于旋转轴的不稳定导致的图像空间分辨率下降的程度 ,从而为确定机械定位精度提供依据 ,首先在理论上推导了基于“平行束投影”和“滤波反投影”算法下 ,旋转轴不稳定对 CT系统点扩展函数 (PSF)的影响 ,并给出了估计这种情况下空间分辨率的方法 ,然后利用 Mathematica4 .0数学计算软件给出了相应的计算机模拟图像。理论估算与计算机模拟图像符合得比较好 ,说明这种对旋转轴不稳定情况下空间分辨率的估计可以作为理论上的一种参考 ,估计结果同时也为大型工业 CT系统中确定转台轴线的径向偏移提供了理论依据。

This paper discusses the negative effect on spatial resolution of computerized tomography (CT) image caused by the random iso center misalignment. Through the theoretic analysis based on 'parallel projection' and 'filtered back projection algorithm', point spreading function of the CT system with nonstationary axis is given, also, the estimate of spatial resolution under such conditions is provided. The simulative image that is generated by Mathematica 4.0 agreed well with the estimate data, which verified that such estimate of spatial resolution with nonstationary axis is valuable. The result also provides theoretic reference for confining the radial deviation of the rotating axis in large CT system.