浅谈CT

 CT(ComputedTomography)是计算机断层摄影技术的简称,它是自X射线在医学领域应用以来一个划时代的成就,是近代飞速发展的计算机技术和X射线成像检查技术相结合的产物。CT的发展历程CT图像是通过数学重建技术完成的。早在1917年,奥地利数学家J.Radon就从数学理论上证明了二维或三维物体可以通过其无限多个投影的集合唯一地重建图像。1938年德国的CabrielFrank首先在X线诊断中用光子方法进行图像重建。     

豪斯费尔德（Hounsfield，Godfrey N，1919-2004）英国工程师（Engineer，England）

豪斯费尔德是计算机断层成像（CT）机器的设计者。用X射线照射人体，再检测透射后的强度，经计算机用卷积反投影法或快速傅里叶变换处理数据，然后重组人体断层图像。CT对人体内病灶的显示比X光照片清楚得多，因而能看出X光检查不到的病灶，如脑内出血。CT于1972年首次临床试验成功，因此豪斯费尔德与CT理论的奠基者科马克共享1979年诺贝尔生理学和医学奖。邮票H27右下缩微印刷的文字是“CT扫描和NMRI（核磁共振成像）使医学诊断技术发生革命性的变化”。     

相干X射线衍射成像技术及在材料学和生物学中的应用

无损获取高分辨率、高衬度微纳米材料结构图像,并能够原位、定量分析是X射线成像技术发展方向之一.最新发展起来的相干X射线衍射成像技术,也称为无透镜成像技术,为实现这一目标提供了可能.本文介绍了相干X射线衍射成像技术的成像原理和发展过程,以及在材料学和生物学中的一些典型应用和最新进展,例如掺杂铋元素在硅晶体中的分布成像,GaN量子点壳层结构的三维高分辨成像,染色大肠杆菌的二维成像,鱼骨的二维成像及矿化机理研究,单个未染色疱疹病毒的二维高衬度成像,未染色酵母菌细胞的三维高分辨成像及原位定量分析.最后对相干X射线衍射成像技术的发展方向做了展望.随着X射线自由电子激光的应用和冷冻技术与相干X射线衍射成像技术的结合,相干X射线衍射成像技术将得到快速的发展和广泛的应用.     

利用对称区域生长算法实现三维ICT图像的快速分割

图像分割作为一种基础的分析手段在工业计算机断层(Industrial Computed Tomography,ICT)检侧中有着广泛的应用.随着CT扫描方式从二维断层扫描向三维立体扫描的发展,对于CT图像的分析也由二维图像处理发展为三维序列图像处理,所以传统的图像分割手段已经不能很好地适应这种需求了.以目前在计算机视觉...     

科马克（Cormack,Allan M，1924-1998）美国物理学家（Physicist，America）

科马克是计算机断层成像（CT）理论的奠基者。用X射线照射人体，再检测透射后的强度，经计算机用卷积反投影算法或快速傅里叶变换处理数据，然后重组人体断层图像。CT对人体内病灶的显示比X射线照片清楚得多，因而能看出X射线检查不到的病灶，如脑内出血。CT于1972年首次临床试验成功，因此科马克荣获1979年诺贝尔生理学和医学奖。邮票C23是计算机断层成像（CT）图。     

1975 年11 月25 日：全身计算机断层扫描的专利

 当德国物理学家伦琴（Wihelm Roentgen, 1901 年获得诺贝尔奖）意外地于1895年发现了他的阴极射线管会放射出X 射线后, 此现象很快地在医学成像与诊断上找到了实际的应用, 但进一步利用它于一种新的、改良型的诊断成像形式--计算机辅助的断层摄影法, 或称计算机断层扫描（CAT Scanning）--却是差不多80 年后的事情了。     

射线平板探测器成像系统的数理模型

非晶硅X射线数字平板探测器是目前唯一可取代胶片照相的新型技术,对其成像特性的研究已成为高像质的DR和三维CT检测技术的基础。目前X射线成像系统均是以线性时不变理论作为分析基础的。基于X射线平板探测器成像系统、成像机理和几何参数建立了成像系统的点扩展函数(PSF)。用圆柱体等效二维PSF模型,使成像系统退化为比例系统,从而把复杂的反卷积运算转化成用代数方程来求解,能够快速实现通过探测器输出图像来估计透照工件的二维输入图像。此模型的建立为在实际检测中利用输出的图像通过线性变换得到输入估计。在DR系统中,基于上述数理模型建立了灵敏度模型,利用输出场强可以很好的再现输入场强。     

基于光栅相衬成像的扇束螺旋CT重建算法

X射线相位衬度成像具有极高的灵敏度,能探测到轻元素样品的内部结构,在医学、生物学和材料科学等众多领域显示出良好的应用前景。光栅成像模式可使用非相干光源进行X射线相位衬度成像,开创了非相干光源相衬成像新纪元。将螺旋CT的概念引入光栅相衬成像领域,将螺旋CT的高效率优势与光栅相位成像的高衬度优势相结合,发展X射线螺旋相位CT方法。通过分析螺旋轨迹非相干光源相位成像的特点,提出一种扇形束螺旋条件下的相位信息提取方法;而后借鉴希尔伯特滤波反投影重建算法的思想,得到扇形束螺旋相位CT重建算法。该算法利用折射角像直接重建物体的相位项。计算机仿真实验证明了该算法的有效性。     

基于MARS系统的X射线能谱K-edge特性CT成像技术

针对传统的X射线CT系统因采用积分探测器难于鉴别材质的关键技术问题,基于MARS系统的X射线能谱CT,开展了X射线能谱K-edge特性的CT成像技术研究。通过对单一材质和混(复)合材质组成的物理模型的多个X射线能量段进行CT断层扫描,获得了材质的K-edge特性曲线,以此重建出了材质的CT图像。借助材质K-edge特性的CT断层图像,可以进行材质的鉴别分析或进行更多的材质认知信息的分析研究。与传统的X射线CT技术相比较,它可以提供更为丰富的X射线衰减信息。     

同步辐射X射线三维显微成像

本介绍了利用同步辐射进行X射线三维成像的工作原理及进展状况,详细论述了X射线三维成像的两种方法,X射线全息及CT技术,以及通过两的结合（HCT）进行高分辨率三维成像的有关理论与实验技术;介绍了同轴全息中消除“双生像”噪声的数字方法,讨论了影响分辨率的各种因素;本还介绍了在国家同步辐射实验室软X射线实验站进行的生物样品X射线三维成像的实验及其结果。     

高分辨率快速数字化光声CT乳腺肿瘤成像

提出了一种基于聚焦线性阵列探测器的快速光声计算机断层成像技术（光声CT）.在光声二维图像重建中,根据阵列探测器机械扫描和电子扫描相结合的组合扫描模式,提出了改进的有限场滤波反投影重建算法.一方面该算法适合多元探测器旋转扫描模式,另一方面探测器的指向性函数作为反投影的权重因子提高了系统的横向分辨率.同时,该成像系统还利用柱面声透镜实现Z轴方向上的聚焦扫描以实现三维层析成像.实验中,这套成像系统空间分辨率达到0.2mm,Z轴方向分辨率为1.5mm,扫描一幅二维图像仅需150s,得到 关键词： 光声CT 有限场滤波反投影算法 声透镜聚焦 乳腺肿瘤检测     

Potential of propagation‐based synchrotron X‐ray phase‐contrast computed tomography for cardiac tissue engineering

Hydrogel‐based cardiac tissue engineering offers great promise for myocardial infarction repair. The ability to visualize engineered systems in vivo in animal models is desired to monitor the performance of cardiac constructs. However, due to the low density and weak X‐ray attenuation of hydrogels, conventional radiography and micro‐computed tomography are unable to visualize the hydrogel cardiac constructs upon their implantation, thus limiting their use in animal systems. This paper presents a study on the optimization of synchrotron X‐ray propagation‐based phase‐contrast imaging computed tomography (PCI‐CT) for three‐dimensional (3D) visualization and assessment of the hydrogel cardiac patches. First, alginate hydrogel was 3D‐printed into cardiac patches, with the pores filled by fibrin. The hydrogel patches were then surgically implanted on rat hearts. A week after surgery, the hearts including patches were excised and embedded in a soft‐tissue‐mimicking gel for imaging by using PCI‐CT at an X‐ray energy of 25 keV. During imaging, the sample‐to‐detector distances, CT‐scan time and the region of interest (ROI) were varied and examined for their effects on both imaging quality and radiation dose. The results showed that phase‐retrieved PCI‐CT images provided edge‐enhancement fringes at a sample‐to‐detector distance of 147 cm that enabled visualization of anatomical and microstructural features of the myocardium and the implanted patch in the tissue‐mimicking gel. For visualization of these features, PCI‐CT offered a significantly higher performance than the dual absorption‐phase and clinical magnetic resonance (3 T) imaging techniques. Furthermore, by reducing the total CT‐scan time and ROI, PCI‐CT was examined for lowering the effective dose, meanwhile without much loss of imaging quality. In effect, the higher soft tissue contrast and low‐dose potential of PCI‐CT has been used along with an acceptable overall animal dose to achieve the high spatial resolution needed for cardiac implant visualization. As a result, PCI‐CT at the identified imaging parameters offers great potential for 3D assessment of microstructural features of hydrogel cardiac patches.     

Proton computed tomography as a tool for proton therapy planning: preliminary computer simulations and comparisons with x‐ray CT basics

Proton beams can destroy tumors better than other radiation treatment options because they deliver their energy in a very accurate way, while leaving the surrounding tissue undamaged. However, it requires a very accurate prediction of the Bragg peak position within the patient's body. In existing proton treatment centers, the dose calculations are performed based on x‐ray computed tomography (CT) and the patient is positioned with x‐ray radiographs. During the 1970s and early 1980s, it was shown that the use of proton beams rather than conventional x‐rays could have some advantages. With the development of specialized medical proton gantries at Loma Linda University Medical Center (USA) and several other proton treatment centers worldwide, interest in this question has been renewed. The modern approach has advanced from simple proton film radiography to CT reconstructions from proton energy loss measurements employing individual proton tracking techniques. This permits image degradation due to multiple Coulomb scattering, one of the main problems of proton CT, to be reduced. Current work is devoted to the comparison of conventional x‐ray CT and proton computed tomography (pCT) as two alternative tools for measuring the physical properties of the human body, required for proton treatment planning. In this paper, a brief comparative overview of the physical basics of both methods are followed by the analysis of Monte Carlo simulation results. The first‐generation CT scheme was assumed for simplicity. The precisions relative to water volumetric electron density distributions, extracted from CT and pCT images, and the sources of absolute errors are discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

T-ray computed tomography

We demonstrate a tomographic imaging modality that uses pulsed terahertz (THz) radiation to probe the optical properties of three-dimensional (3D) structures in the far-infrared. This THz-wave computed tomography (T-ray CT) system provides sectional images of objects in a manner analogous to conventional CT techniques such as x-ray CT. The transmitted amplitude and phase of broadband pulses of THz radiation are measured at multiple projection angles. The filtered backprojection algorithm is then used to reconstruct the target object, including both its 3D structure and its frequency-dependent far-infrared optical properties.     

基于能量最小化的肾脏计算断层扫描图像分割方法

随着成像技术的不断发展, 医学图像处理在计算机辅助诊断和病变管理中的重要作用日渐突出, 而计算断层扫描序列图像的肾脏组织分割是其中的关键步骤. 本文结合肾脏序列图像的连续性特征, 提出了一种基于活动轮廓和图割方法的能量最小化分割模型来自动分割肾脏组织. 根据相邻切片图像的形状差异与层间距之间的关系, 计算出序列图像中适合图割优化能量函数的最优范围. 能量函数采用测地活动轮廓模型和Chan-Vese模型的综合形式, 兼顾了目标的边界和区域信息. 随后, 利用图割方法优化离散化的能量函数, 驱使活动轮廓逐渐向目标边界靠近, 直至收敛为止. 对30组腹腔序列图像进行了算法测试, 实验表明基于能量最小化的分割方法能够有效地提取出序列图像中的肾脏组织, 其分割结果的平均Dice系数达到了93.7%. 关键词： 计算层析 肾脏分割 能量最小化 连续性     

数字式X射线辐射扫描成像系统及其应用

数字化图像具有非常突出的优点和广泛的应用,而Ｘ射线成像在医学诊断和工业无损检测等领域占据非常重要的地位,因此Ｘ射线成像的数字化必将成为一种趋势。文章介绍了数字式Ｘ射线辐射扫描成像的特点、原理及其应用前景。采用气体电离室探测器阵列完成了３２路数字式Ｘ射线辐射扫描成像装置系统,其空间分辨率达到０．５ｍｍ,并且获得了比较满意的Ｘ射线图像效果。     

Dual-modal photoacoustic/CT imaging system

Photoacoustic(PA) tomography(PAT) breaks the barrier for high-resolution optical imaging in a strong lightscattering medium, having a great potential for both clinical implementation and small animal studies. However,many organs and tissues lack enough PA contrast or even hinder the propagation of PA waves. Therefore, it is challenging to interpret pure PAT images, especially three-dimensional(3 D) PA images for deep tissues, without enough structural information. To overcome this limitation, in this study, we integrated PAT with X-ray computed tomography(CT) in a standalone system. PAT provides optical contrast and CT gives anatomical information. We performed agar, tissue phantom, and animal studies, and the results demonstrated that PAT/CT imaging systems can provide accurate spatial registration of important complementary contrasts.     

中子半影成像的计算机断层重建技术

实际用于中子半影成像重建的方法都是线性方法,而计算机断层重建是一种能够用于中子半影成像重建的新方法.介绍了中子半影成像的断层重建原理,将半影成像的诊断图像沿径向等角度提取、微分后就可以使用断层重建方法重建.给出了使用卷积反投影方法重建不同噪声诊断图像的结果,并分析了断层重建的优缺点.重建结果表明,断层重建方法能够重建出...     

基于Micromegas探测技术的中子CT可行性研究(英文)

在培育新品种过程中能够实时掌握了解土壤中植物根系的形态以及其生长情况将为植物学家提供很多不可或缺的信息。对基于 micromegas 探测技术的中子 CT 在这一新应用的试验环境进行了仿真模拟, 通过三维图像重建后,得到了令人满意的预期结果。首先通过 Geant4 和 Garfield 模拟计算利用聚乙烯薄膜作为中子转换层的 micromegas 中子探测器, 得到了非常理想的位置分辨, 说明基于micromegas 探测技术建立中子 CT 照相系统的可行性。 然后利用MCNP仿真模拟14 MeV 中子CT 的实验环境, 最后由Matlab程序进行图像重建。In this paper, the possibility using micromegas(Micro Mesh Gaseous Structure) as neutron detector in 14 MeV neutron computed tomography(CT) has been simulated. The results show that the micromegas neutron detector has high spatial resolution and is a good candidate for neutron radiography. The three dimensional images of plant roots in soil are successfully and clearly obtained by the 14 MeV neutron CT with micromegas as a neutron detector. In the present simulation, MCNP is employed for 14 MeV neutron transport in the sample and Matlab for the 3 D photograph reconstruction.     

Comparison of in vitro breast cancer visibility in analyser‐based computed tomography with histopathology,mammography, computed tomography and magnetic resonance imaging

High‐resolution analyser‐based X‐ray imaging computed tomography (HR ABI‐CT) findings on in vitro human breast cancer are compared with histopathology, mammography, computed tomography (CT) and magnetic resonance imaging. The HR ABI‐CT images provided significantly better low‐contrast visibility compared with the standard radiological images. Fine cancer structures indistinguishable and superimposed in mammograms were seen, and could be matched with the histopathological results. The mean glandular dose was less than 1 mGy in mammography and 12–13 mGy in CT and ABI‐CT. The excellent visibility of in vitro breast cancer suggests that HR ABI‐CT may have a valuable role in the future as an adjunct or even alternative to current breast diagnostics, when radiation dose is further decreased, and compact synchrotron radiation sources become available.