Calibration and Correction Method of the Deflection Angle of Rotation Axis Projection on Neutron Tomography

For neutron tomography, reconstruction accuracy greatly relies on exact registration of the projection and the back-projection coordinate system. Since the manufacturing and installing errors of mechanical components make the rotation axis projected in CCD camera deflect a certain angle, a mismatch between the projection coordinate and the detector coordinate will be caused consequently, resulting in obvious artifacts on the reconstructed images. In this paper, a calibration and correction method of the deflection angle of rotation axis projection is proposed to eliminate artifacts on neutron tomography images. First, all the projections among 360° rotation range are superposed together to create an averaged image with a unique symmetry axis. Then by segmentation and principal component analysis on the averaged image, the deflection angle is figured out. The calibrated angle is introduced to the reconstruction algorithm as an extra correction parameter, and artifacts-free images are finally obtained.