扇束CT几何伪影的校正方法

摘要

实际工业CT系统很难满足经典CT图像重建公式所要求的射线源焦点、转台中心及线阵探测器之间严格的对准关系.不满足对准关系将导致经典CT图像重建公式所重建的图像中出现几何伪影.本文引入可以描述一般情况下CT扫描几何关系的一组几何参数,给出了由金属丝的投影数据间接估计这些几何参数的方法,还给出了基于这些几何参数的图像重建公式.本文只假设转台的旋转轴垂直于由射线源焦点与线阵探测器所形成的扇束,而不要求扫描系统满足其它几何对准关系.对于扫描系统不对准的情况,先按照本文方法估计几何参数,再将其代入本文提出的图像重建公式,便可以正确重建出被测物的断层CT图像.%For a real industrial CF system, it is very difficult to meet the rigorous aligned relations among the X-ray focus, the rotation cener of turntable and the linear detector, which is required by the conventional image reconstruction formula. Misalignment will result in geometric artifacts in the image reconstructed by the conventional image reconstruction formula. In this paper, we first introduce a set of geometric parameters which fully describe general CT scanning configuration, and then propose an indinect method to estirmate the set of parameters from the projection date of a meta sikl.We also propose a generalizad filtered back-projec-tion (FBP) reconstruction formula based on such set of parameters. In this paper, we assume that the rotation axis of the CT turntable is vertical to the fan-beam forned by the X-ray focus and the linear detector array,but do not require that the CT scanning system satisfies other alignment relations. For a misaligned scanning system, we can first estimate the pararneters by our method,and then reconstruct the image conrectly using our reconstmction formula with the estimated parameters.