A new method to determine the center of rotation shift in 2D-CT scanning system using image cross correlation

Center of rotation (COR) is one of the most important factors that affect the image quality of CT system. In this paper we propose a new method that is based on image cross correlation to accurately measure the shift of COR in 2D-CT (Two Dimensional Computed Tomography) system. In this method, we firstly rebin the fan-beam sinogram to parallel beam sinogram. Based on the symmetry characteristic of two projections that are 180° opposed to one another in the parallel beam sinogram, we then divide the rebinned sinogram equally into two sub-sinograms along rotating angle direction. After that we flip the second sub-sinogram in right direction, and apply the cross correlation operation to the first sub-sinogram and the flipped sub-sinogram to get the shift of COR. This method does not need the calibration sample, and just uses the sinogram of the scanned slice to calculate the shift of COR directly. The experimental results prove that this method is of high accuracy and anti-noise ability and is easy to implement.