【作者】 陈平；

【导师】 潘晋孝；

【作者基本信息】 中北大学 ， 信号与信息处理， 2009， 硕士

【摘要】 虚拟CT系统能够设计和优化系统的装配性能参数,辅助硬件系统的设计和优化,同时对实际实验中的参数预设提供了一个指导性的意见,为重建精度和质量分析提供先进的CT非接触无损检测手段和关键技术,因此其仿真技术逐渐成为学者们研究的热点。本文正是以虚拟CT系统为研究对象,对虚拟CT系统成像过程的物理特性进行深入挖掘刻画,并将其融入CT成像过程仿真中,建立更能逼真反映实际CT成像过程的仿真模型,进而为虚拟CT系统研究提供可靠的数据支撑,提升虚拟CT系统的实际应用性。首先,在分析CT成像与仿真的原理基础上,对X射线产生过程进行了仿真;并以此为基础,分析CT成像系统中X射线的连续谱分布、材料衰减系数与射线的能量之间的关系、射线源焦点尺寸等物理因素对投影过程的影响,并将此类物理因素融入投影过程仿真模型,提出了基于连续X射线谱的投影仿真算法。在投影仿真模型的实现过程中采用了自适应辛普生能谱抽样技术,该技术可以根据X射线的谱分布的走势自适应离散求和,从而在仿真精度及速度上有较大提高。其次,在X射线CT成像过程中,由于散射影响,其图像的对比度降低,边缘模糊,为此在虚拟CT系统中应融合散射仿真模块,以便更逼真地反应实际CT系统的成像过程。本文根据X射线与物质相互作用与否以及散射对CT图像的影响,提出了一种脱离投影过程的简便有效的散射过程仿真技术——基于ICA图像融合的虚拟CT系统散射仿真技术。该技术是利用ICA图像融合技术,实现无散射CT图像和根据先验信息以及散射退化模型所确立的散射图像之间的融合,进而实现虚拟CT系统散射过程仿真。最后,通过仿真实验对上述仿真方法进行验证。实验表明:上述X射线产生过程、投影过程以及散射过程的仿真方法具有一定的可行性,能逼真地反映真实CT成像过程,进而为整个虚拟CT系统研究提供了可靠数据支撑。更多还原

【Abstract】 Virtual CT (Computed Tomography) simulation system become research focus, because it can design and optimize assembly performance parameter of the CT system, help design and optimize the hardware system, provide instructive suggestions for parameter hypothesis in the actual experiment, provide the method and key techniques of non-contact CT detection for the reconstruction precision and quality analysis. By taking virtual CT system as research object, this paper extracts and depicts the physical properties for virtual CT system imaging process. Then this paper integrates these physical properties into the procession simulation of virtual CT imaging, and establishes the simulation model which realistically reflect the actual the process of CT imaging. This model can provide the credible data for the research of visual CT system, and upgrade the applicability of virtual CT system.Firstly, based on analyzing the principle of CT imaging and simulation, the emission process of X-ray is simulated. By taking this simulation result as basic, some physical factors of CT imaging system are analyzed and integrated into the simulation model of projection process, which are the distribution of X-ray spectrum, the interaction with material’s attenuation coefficient and the X-ray energy, the influence of radiation source focus size in radiography, and so on. Then the simulation algorithm, based on consecutive spectrum, is presented. In the realization process of projection simulation, the method of spectrum sampling is adopted based on adaptive Simpson. This method can adaptive add the spectrum according to the uptrend of energy spectrum distribution. So it can improve the precision and speed of simulation.Secondly, in the process of X-ray CT imaging, because of the impact of scatter, the contrast of CT image becomes low, the edge of CT image blur. So in the visual CT system, it is necessary that scatter is simulated, which can realistically reflect the actual the actual CT imaging system. This paper offer a handy and effective scatter process simulation method, which is the method of scatter simulation about virtual CT system, based on images fusion using ICA (Independent Component Analysis), according to the interaction with substances and X-ray and scatter impact for CT image. This method use ICA image fusion to realize images fusion, which are scatter-free image and scatter image, which are established by prior information and the model of scatter degradation. So the scatter process simulation about virtual CT system is realized.At last, the above simulation method is validated by simulation experiment. The results show the simulation method of X-ray emission, projection process and scatter process is viable. It realistically reflects the actual CT imaging system, and offers the credible data for the research of visual CT system.更多还原