【作者】 李真；

【导师】 任秋实； 杨昆；

【作者基本信息】 河北大学 ， 仪器仪表工程， 2014， 硕士

【摘要】 本文基于多模态小动物分子医学影像系统项目，该项目旨在将X射线断层成像（CT）、正电子发射断层成像（PET）、单光子发射断层成像（SPECT）、荧光分子层析成像（FMT）四种成像模态同一系统中进行整机集成和同机融合。锥束CT（Cone Beam CT）又称Micro-CT、小动物CT，其成像原理基于X射线衰减特性，能够实现微米级别的三维重建图像分辨率。锥束CT能够实现无创、在体的解剖学成像（或功能成像），超高的分辨率使锥束CT技术自诞生起便受到广泛的关注和迅速发展。锥束CT技术是基因治疗、肿瘤研究、药物开发以及材料学、工业无损检测等领域的重要研究手段。本文主要工作针对锥束CT的几何校正，设计专用的校正模体，通过模体的成像特点判断系统的几何误差，并对系统硬件进行调节，以最大限度减小系统的几何误差。本文首先介绍了锥束CT系统的高性能特点和以及其在多种领域中起到的重要作用，以及系统几何误差的产生和其对锥束CT重建图像质量的影响，并介绍了目前国内外关于锥束CT系统几何校正的研究现状。其次，介绍了锥束CT的工作原理和系统结构与硬件组成，并介绍了FDK三维重建算法的原理及其对锥束CT系统中硬件几何关系的要求。然后重点分析了本文所使用的立式锥束CT系统的几何特点，对系统的几何误差参数进行了讨论。并针对现有的锥束CT设备，详细介绍了本文所设计的校正模体和校正方法原理，以及具体的校正实验过程。为了表明该校正模体和方法的有效性、可行性，本文设置了使用另一种模体和校正方法的对比实验，并且从理论上分析了两种方法的校正误差精度，数据表明两种方法具有可比性。使用经过两种方法校正后的锥束CT系统对同一铜丝进行重建，对比其断层重建图像的质量。结果证明两种方法都能够有效减小锥束CT系统几何误差，消除重建图像中几何伪影，而本文设计的模体和校正方法比对比实验的方法的重建图像分辨率更高。进一步的，分别使用校正前后的锥束CT系统对相同的QRM标准模体进行扫描重建，进一步验证本文设计的点线环模体校正方法的有效性。使用该标准模体可直观地评估锥束CT系统的空间分辨率，且对模体重建的剖面图表明，经过本文方法进行几何校正后的锥束CT系统，径向空间分辨率已达到50μm <r <100μm。该数值已达到并高于项目初始目标所设定的150μm标准。最后，使用经过几何校正的锥束CT系统对鸡爪骨骼结构进行三维重建，从重建图像中可清晰地观察到每块骨骼的形态结构，甚至骨骼表面微小凹凸。对海螺、皮皮虾、鲫鱼的三维重建结果也显示，系统的重建图像空间分辨率比较高。实验证明该方法校正精度很高，能够满足实际工程需要。更多还原

【Abstract】 This paper’s work is on the base of Medical Molecular Imaging System of Small Animal,which is a project aiming at combining four imaging modules into one integrated imagingsystem. The four modules include CT (Computed Tomography), Micro-PET (PositronEmission Tomography), SPECT (Single-Photon Emission Computed Tomography) and FMT(Fluorescence Molecular Tomography). The focus of this paper is the geometric calibrationmethod of the CT part, a CBCT (Cone Beam CT). CBCT is also known as Micro-CT or smallanimal CT, and it’s an anatomical or structural imaging technique while its imaging principleis based on X-ray attenuation. CBCT has advantages of non-invasive and in-vivo imaging,especially the high3D reconstruction resolution at the micron scale, which make it gainsextensive attention and rapid development since born, and has become an important researchmean in gene therapy, cancer research, drug development and materials science, industrialNon-Destructive Testing area.In this paper, a dedicated calibration phantom was designed to calibrate the geometricmisalignment of the CBCT system. The features of the phantom’s projects were used toestimate the geometric misalignment parameters of the system and then adjust the deviceswhich includes the X-ray source and the flat panel detector to right positions. The purpose ofthis method is to minimum the geometric misalignment of the CBCT system as best aspossible.This paper introduced the high performance of CBCT and its important role in multipleareas, then the generation of geometric misalignment of CBCT system and the degradation itcaused on the quality of reconstruction images. The research status at home and abroad ofCBCT geometric calibration has been presented also.The operating principle, system constitution of CBCT and main performance of devicessuch as X-ray source and flat panel detector has been discussed then, also the theory of FDKreconstruction algorithm and its demanding requirements to CBCT system geometry. Then this paper analyzed the geometric characteristics of CBCT system with a verticalstructure, and discussed the geometric parameters of a system with misaligned geometry.Based on the existing CBCT system, the characteristics of the calibration phantom which hasbeen designed dedicatedly and its calibration principle have been presented, also the details ofexperiment process. In order to prove the feasibility and validity of this method, anotherphantom was used to calibrate the same system as a comparison experiment. The theoreticalanalyses of alignment accuracy indicated that the two methods are comparable and thededicated phantom should bring a better effectiveness. The tomographic reconstructionimages of a copper wire indicate a high calibration accuracy of the two methods, and thecomparison between the images of two methods proves obviously greater accuracy and higherresolution of the method of the dedicated phantom. Furthermore, a QRM micro-CT phantomwas scanned and reconstructed by this CBCT system before and after it was calibrated by themethod of the dedicated phantom, with the purpose of proving the effectiveness of the methodmore quantifiably. The QRM phantom is a standard phantom, which can be used to assess thespatial resolution of CBCT system intuitively. And according to the reconstruction of theQRM phantom’s section, the calibration method of the dedicated phantom has achieved a highspatial resolution which is lower than50μm but higher than100μm, and this is higher than150μm, the expected standard when this CBCT system was designed at the beginning.In the end, a chicken feet was scanned by the CBCT system after it was calibrated toreconstruct the bones. From the reconstructed images, the size and shape of each bone can beobserved clearly, even the minute depressions on the surface of each bone. The reconstructedimages of a conch, a mantis shrimp, and a crucian also show that the spatial resolution of thereconstructed images is relatively high. Experiments prove high calibration accuracy and highreconstruction resolution, and well meets the requirement of practical application.更多还原