Study On The Technology Of High Energy X-ray Industrial Computed Tomography Based On Area CCD Cameras

The cross section of large industrial components can be reconstructed using high energy X-ray industrial computed tomograpgy (ICT). It is absolutely necessarily equipment in manufacturing industry, such as national defense, aeronautics and astronautics industry. According to the structure of detectors in the CT scanner, ICT can be divided into two types: the ICT based on linear-array detectors and the ICT based on area-array detectors. To satisfy industrial actually requirement in our country, the technology of high energy X-ray ICT based on area-array detectors is selected as research object in this paper.Firstly, the characteristic of high energy X-ray detection and the relation among spatial resolution, density resolution, X-ray intensity and exposure time are analyzed. ICT system based on area-array CCD camera is designed in which the application range of the filtered back-projection reconstructed algorithm with parallel beam, fan beam or cone beam is considered. Causes to result in projection data nonuniformity include the vignetting effect resulted from the irradiation intensity distribution of the accelerator and the lens of CCD camera, the peak noise of CCD dark current and the inner defect of converter screen, and the corresponding correction methods are presented. Then multi-slice images of three typically large components used in the tank including large diameter cannonball, impeller and cylinder cover are reconstructed in the ICT system.Secondly, every cause resulting in reconstructed image artifacts during obtaining projection and reconstructing image is studied, such as the length selection of the filter, rotation center deviation, vignette in the imaging system, CCD dark current, pulse noise and scatter in this paper. The corresponding methods to remove image artifact are given.Finally, the reconstruction error using truncated projections is researched while the object which size is bigger than the projection field of view is scannedin the ICT system. A reconstruction method complementing the truncated projection by means of prior knowledge of the object, then reconstructing CT image is proposed in this paper.