Study On Error Correction Algorithm Of Geometric Parameters Of Cone-beam Industrial CT System

CT(Computer Tomography) is widely used in medical diagnosis, industrial detection, security and so on for its non-destruction, accuracy and convenience. It is imaging with the principle that objects of different composition and thickness attenuates differently to X-Ray. In various applications of CT detection, the quality of the reconstructed image is a problem people most concern about. The forms of the error of different geometric parameters in the reconstructed image is significant to the determination of geometric parameters, and the installation of the main components of the system and the accuracy of related geometric parameters are important factors that affect the quality of the reconstructed image. The correction to the error of geometric parameters of the C T system is also called geometric parameters’ calibration of the system, with the help a specially designed model, the geometric parameters of the CT system is calculated according to the projection of the model. The accurately calibration of geometric parameters of cone-beam CT system with circular trajectory forms the main research contents of this article.Firstly, in this paper, we attribute the error of the geometric parameters of the system to the deviation of the detector. With the point model, we analyzed the influence of the geometric parameters of the system on the reconstructed image, and the quantitative relationships between the deviation of various geometric parameters and the reconstructed point coordinate were given, then we study the influence of the deviation of system geometric parameters on the reconstructed image through simulation experiments. In addition, we design a model that can judge whether the detector has the in-plane rotation, and can also calibrate the position of the detector unit that the detector plane intersects with the line contact the source and the center of the rotation axis. And the deviations of these two parameters are the biggest factors that influence the quality of reconstructed image. Furthermore, we can also adjust the system according to projected image of the model so that the system in an ideal state as much as possible.Secondly, we give a method to calibrate all geometric parameters of the cone-beam CT system. With the projected images of a specially designed model we calibrate all of the seven geometric parame ters of the system. The model consists of a series of ball which can be regard as a point. The method was implemented in two steps. In the first, we need the projected image of the model under four special degree, with these image, we can calibrate the five main geometric parameters of the system. In the next step, we can calibrate the two out-of-plane rotations with the projected image of the model under a special degree. Then we verify the correctness and effectiveness of the method through computer simulation.Finally, we introduce a method to correct the system geometric parameters. With this method and the geometric parameters calibrated by the calibration method, we can correct the projected data of the object that scanned under the system with deviation. Using the corrected projected data, the geometr ical artifacts of the reconstructed image was eliminated and the quality of the reconstructed image was improved. We verify the validity of the method through computer simulation.