Automatic measurement of rotation center for laminography scanning system without dedicated phantoms

With a particular function in plate-type structure tomography, computed laminography (CL) has received increasing attention in industrial nondestructive testing and become an important branch of computed tomography (CT). For the reconstruction algorithm of CL, center of rotation (COR) is the most important parameter determining the reconstruction accuracy and must be located precisely. Otherwise, even a tiny error of COR will cause obvious artifacts in reconstructed images. In order to realize measurement of COR with high accuracy and efficiency, a feasible calibration method was proposed to determine the position of COR without dedicated phantoms. According to this method, when a sample fixed on the rotational stage turns around the rotational axis, the locus of the sample’s projection on the imaging plane will be an ellipse. Consistent with the symmetrical property of an elliptical image, a cross-correlation operation is adopted to determine the position of COR by locating the peak value of the cross-correlation function. The computer simulation and experimental results demonstrate that this method has high accuracy, and strong anti-noise and anti-wobble ability. In particular, this method does not need a dedicated phantom to perform the calibration, but rather uses projections of the inspected sample to calculate COR directly.