Spatial Registration of X-ray CT Projection Images

The relative displacement among X-ray source, rotation stage, and detector in X-ray computed tomography(X-ray CT) imaging process are difficult to eliminate. This causes spatial misalignment of the projection and flat-field images, which directly affects the accuracy of flat-field subtraction and the subsequent CT reconstruction. In this paper, the quantitative spatial displacement was obtained between each projection image and the detector using a cross-correlation method. The projection images registrations were carried out according to the calculated displacement. As this method is very sensitive to image gray value, a polynomial fitting method was used to correct the non-uniform illumination in the original CT image. The numerical results based on real CT data have demonstrated that this method can effectively correct the misalignment of CT projection images, caused by relative movement among the X-ray source, the rotation stage and the detector.