Industrial X-ray Ct Imaging Related Issues

Industrial CT (Computerized tomography) as an advanced nondesrtuctive testing technology has a wide range of applications in aerospace, weapons, cars, electronics, security and many other fields. In order to meet the requirements of industrial CT applications, we have studied Polychromatic CT Imaging and Incomplete-data CT Imaging. The main work of this paper is as follows.(1) Indirect measurement of X-ray spectrumWe propose an indirect measurement method to estimate the spectrum of X-ray source via the transmission data of a known wedge phantom. We transform the problem into a regular optimization problem, in which the regularization item is designed based on the physical properties of X-ray tube target. Through simulation experiment, we analyze the effect of the material and thickness of the inspected object at the common voltage on X-ray energy spectrum, and then suggest reference choices on the material, width and length of the phantoms. The numerical results show that the proposed method is valid to estimate X-ray spectrum from data simulated by GEANT and scanned on real CT device.(2) The well-posedness of dual-energy CTFirst we analyze the properties of contours of the dual-energy projections. And then, we give a numerical approach to solve contours from two sets of ordinary differential equations. We simulate a series of X-ray spectrums with different characteristics by GEANT. Through analyzing numerically the distribution of contours of the dual-energy projections at different X-ray spectrums, we reveal the well-posedness of the dual-energy equations. We also design an algorithm to solve dual-energy equations. Our method and results may be significant to optimal design of dual-energy spectrum including to the optimization of the material and voltage of the X-tube target, the material and thickness of filter slices, and so on.(3) Image reconstruction from incomplete dataWe develop an improved fast iterative reconstruction algorithm based on the minimization of the image total variation. In the algorithm, conjugate gradient method is applied to solve the minimization of the image total variation (TV), and multi-resolution iterative technique is used in the iteration process. The algorithm can be used to reconstruct CT image from projections at few-views or projections of abnormity components. We perform numerical experiments using both computer-simulation data and real CT data. Experimental results verify that the proposed algorithm not only improves the quality of the reconstructed image, but also significantly accelerates the convergence of the iterative images.(4) Prototype design on narrow-band X-ray sourceIn order to acquire narrow-band X-ray source, we design a prototype of X-ray tube with dual-target structure and verify the validity of the design from Monte Carlo simulations by GEANT. We analyze the intensities and the energy range of the X-ray produced by the prototype of the X-ray tube based on simulation experiments. We also compare the beam-hardening effect of the narrow spectrum X-ray with that of the broad spectrum X-ray. In addition, we analyze how the material compositions of the filters and the thickness to effect the spectrum of X-ray through simulation.