Research On Iterative Algorithm In ICT And Geometric Misalignment Calibration

ICT (Industrial Computed Tomography) can detect the object's layer, without destructing the object, and distinguish the geometry structure, material situation, objection category depending on gray value of object's layers. ICT has formed a relative independent technology domain now. From 1980's ICT is applied widely. Many international industrial developed countries have been using ICT on nondestructive testing and reverse engineering in Aeronautics. ICT is not influenced by the object's material, shape and surface status, at the same time ICT may detect 2D image of object. At present ICT is considered the best method in nondestructive testing field.The ART algorithm transfers this problem into finding the solutions of a linear equation group. When the projection data is incomplete, we can regard it as a linear equation group lacking of several equations. The incomplete projection data is neglected to some extent, thus it can solve the problem very well. Artifacts caused by geometric misalignment not only reduce the quality of reconstruction images, but also hold back the advancement of ICT performances. So it's necessary to correct them.This paper mainly researches algebraic reconstruction algorithms, carries out some of them, gives out the process of achievement. It also analyses several factors, which affect reconstruction speed and reconstruction quality of ART, by simulation experimentation on reconstruction of classic Shepp-Logan head model. The theory analysis and experimental results demonstrate that ART is one of the most effective algorithms of CT imaging, and it has prominent merits in some special reconstruction situations.The other work of the paper is research on calibration of ICT systern. First, the paper analyses some kinds of artifacts and effects caused by geometric misalignment, then a calibration method is proposed. And the principle is also expounded. This approach needs to measure only one projection to estimate all the parameters that totally describe the geometry of a cone-beam CT system, by using a four-point phantom. In addition, there is no restriction on any one of parameters. The accuracy of this method is confirmed by the simulated results. It is proved that this method is applicable and efficient for misaligned scanner geometry.