分能段CT扫描成像算法研究

发布时间：2018-04-11 23:19

本文选题：分能段CT成像 + 灰度阶跃　；参考：《中北大学》2017年硕士论文

【摘要】：X射线CT成像技术是应用于工业无损检测、公共安全检查及医疗诊断等领域的重要手段之一,然而随着科学技术的快速发展,适用于结构分析的传统单能CT成像技术已不能满足目前工业CT对物质对比度的高要求。这是由于在X射线成像系统中,实际X射线源发射的射线是由不同能谱信息组成的连续能谱,而该X射线对被检测物体进行透照以后,因为不同物质具有特殊的特征吸收,所以对X射线的衰减能力也不尽相同。但是常规的重建算法都是基于近似单能能谱的假设下,对采样投影数据进行重建,这种实际数据与仿真数据的不一致性,易导致重建图像出现硬化伪影和金属伪影,降低CT重建质量。为此,国内外研究人员针对双能CT系统和光子计数探测器进行了多能CT重建研究,但都由于成本较高,不易推广应用于实际工程中。鉴于双能CT系统的成像基本数理原理,为了在原有的传统CT系统的基础上,实现多能CT成像的目的,本文研究了一种分能段CT的成像方法。论文基于仿真设计思想,建立了双能段和多能段的分能段CT模型,通过仿真实验对分能段投影数据的特征分析以及对其重建图像的对比度的研究,验证了模型的有效性和分能段CT成像理论与方法的意义。然后针对分能段投影的灰度阶跃,采用精确高频定位的小波分析理论,结合小波低频的灰阶修正小波系数,实现了小波逆变换后投影的灰阶修正,并通过仿真实验验证了该方法的可行性。为了从重建算法上,改进分能段CT成像理论,实现多能段CT成像。最后基于E-ART双能谱CT重建算法,提出了一种分能段CT扫描的多能迭代重建算法,通过仿真实验表明,分能段CT成像不仅能够消除重建图像伪影,而且实现图像内部物质的区分,重建出高质量的图像。
[Abstract]:X-ray CT imaging is one of the most important methods used in industrial nondestructive testing, public safety inspection and medical diagnosis. However, with the rapid development of science and technology,The traditional single-energy CT imaging technique, which is suitable for structural analysis, can no longer meet the high requirement of material contrast in industrial CT.This is because, in an X-ray imaging system, the actual X-ray source is a continuous energy spectrum consisting of different energy spectrum information, and after the X ray is taken into account of the object being examined, because different substances have special characteristics of absorption,So the attenuation ability of X-ray is different.However, the conventional reconstruction algorithms are based on the assumption of approximate single energy spectrum to reconstruct the sampled projection data. This kind of actual data is inconsistent with the simulation data, which can easily lead to the appearance of hardened artifacts and metal artifacts in the reconstructed images.The quality of CT reconstruction was reduced.For this reason, researchers at home and abroad have carried out multi-energy CT reconstruction research on dual-energy CT system and photon counting detector, but because of the high cost, it is difficult to be popularized in practical engineering.In view of the basic mathematical principle of imaging of dual-energy CT system, in order to realize the purpose of multi-energy CT imaging on the basis of the original traditional CT system, this paper studies a kind of imaging method of segmented CT.Based on the idea of simulation design, the CT model of dual-energy segment and multi-energy segment is established, and the feature analysis of the projection data and the contrast of the reconstructed image are studied by simulation experiment.The validity of the model and the significance of the theory and method of segmental CT imaging are verified.Then, aiming at the grayscale step of the energy division projection, the wavelet analysis theory of accurate high frequency location is adopted, and the gray scale correction coefficient of wavelet low frequency is combined to realize the gray scale correction after inverse wavelet transform.The feasibility of the method is verified by simulation experiments.In order to improve the theory of split-segment CT imaging from the reconstruction algorithm, multilevel CT imaging can be realized.Finally, based on the E-ART dual energy spectrum CT reconstruction algorithm, a multi-energy iterative reconstruction algorithm is proposed. The simulation results show that the sub-energy segment CT imaging can not only eliminate the reconstructed image artifacts, but also realize the internal material differentiation.Reconstruct high quality images.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP391.41

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