Research Of Scatter Correction For Cone-beam CT System

Among the methods of acquiring information from the subject inside,computed tomography(CT) has absolute advantages,which can gain projections at different angles and reconstruction images under the premise of non-destruction.From the images internal information or structure of the subject can be analyzed. So the method is widely used in the field of industrial non-destructive testing and medical diagnosis.Ever since CT appeared,the scanning mode of it has changed from pencil-beam to cone-beam. Allowing for the merit of high spatial resolution and utilization of X-ray, the cone-beam CT based on flat panal dector is gradually applied in industrial and medical circles.Due to the Compton effect,the scattered photons in the X-ray detected subject will give rise to severe cupping artifacts in reconstructed images,which lower the quality of images. For seeking an optimum method of the scattering correction,the article include the following sections:(1) Analysis of the mechanism of Compton scattering artifacts, by physical derivation scattering distribution characteristics are obtained. The use of physical computing, Monte Carlo simulation and other means to verify some of the physical characteristics of the initial scattering, common understanding of the domestic and international scatter correction method, laid the foundation for the subsequent scattering Correction of hardware and software.(2) Through the research of domestic and foreign CT scatter correction method, this study selected five of the scatter correction methods, using MCNP to simulate scattering correction effect and through practical experiments to verificate their feasibility under realistic conditions. For 450 kev in X-ray CT system scatter correction effect is quite good, most of the amount of scattering is filtered, but for less than 200 kev following low-energy cone-beam CT system, based on the filter sheet scatter correction scheme is difficult to apply. Option II and option III is based on the fan-shaped baffle and baffle scatter correction program, but due to the introduction of noise so that the edge of the image quality of CT reconstruction of severely affected, and thus the correction program could be improved. For four programs and program V. Programme IV due to the simple operation steps, for low-energy scattering cone-beam CT correction is quite useful, but in actual use, should be between the amount of scattering lead column adjusting plate specifications and calibration plate to make the newly introduced reasonable trade-off to achieve good results, and when the beam energy is too high due to the baffle initial rays penetrate reach scatter correction. Without the restriction of ray source energy, selecting the appropriate scatter correction scheme according to the actual use of the energy of ray source.(3)The scattering cone-beam CT is divided into alternating scattering and basis scattering,through research work on the part of the hard-scatter correction software can filter out alternating scattering, according to two facts of scattering characteristics, estimating of basic scattering by a mathematical formula model, when the object is further filtered substantially thicker scattering component, the actual use of the low-energy cone beam CT detected the object thinner, BSA and BAG are more applicable; the thicker the object, due to scattering a large amount can further select the appropriate correction coefficient using the estimated model based scattering filtered on the basis of the amount of scattering scatter correction on the third chapter, in order to achieve better correction effect.