微焦点X线相衬成像技术的边缘信号增强特性研究

目的：研究确定微焦点X射线相衬成像技术的边缘信号特性,以更好地从理论和实验角度,来解读X射线相衬成像结果中的图像信息,更好地确定基于微焦点的X射线相衬成像设备中的相关成像参数,以提高X射线相衬成像技术的应用效果。方法：本文以X射线的折射现象为物理基础,将菲涅耳衍射理论和傅立叶变换相结合,建立X线相衬图像对物体相位信息的二阶微分理论模型,揭示了微焦点X线相衬成像技术的边缘结构信号增强特性及其内涵。再通过计算机仿真实验和对真实光纤样品的物理实验,来观察和验证X线相衬成像技术的边缘结构信号增强特性。结果：计算机仿真实验和对真实光纤样品的物理实验的一致结果显示：基于微焦点的X线相衬成像技术,对样品的边缘结构信息具有明显的信号增强特性,通过相衬图像能够突出显示弱对比物体内部结构的边缘信息。结论：X线相衬成像是一种全新的成像方法,它弥补了传统成像方法在对弱吸收物质成像上的不足,研究证实,这种技术具有对样品内部的微细结构进行边缘增强的成像特性,这为进一步的技术开发和设备参数的优化提供了很好的研究基础。     

微焦点类同轴X射线相衬成像实验及相位恢复重建

目的:基于微焦点X射线源,进行相衬成像实验和相位信息提取。方法:根据Fresnel-Kirchhoff衍射理论,考虑空间相干性与时间相干性的影响,对连续X射线相衬成像的一般公式进行推导。根据从含有相位信息和吸收信息的图片里提取纯相位信息的方法,通过MATLAB对相衬图片进行处理。结果:实验一,对塑料吸管进行相衬成像,通过改变探测器与样品之间的距离,得到比传统X射线成像更清晰、放大且能够突出边界信息的图像;实验二,在电压分别为45 kVp和70 kVp的情况下得到硼硅酸盐玻璃的相衬图像,然后通过相位恢复重建得到含有纯相位信息的相衬图像。结论:对于轻元素物质,微焦点类同轴X射线相衬成像比传统X射线相衬成像的分辨率高、图像衬度好;相位信息提取技术将会大大促进微焦点类同轴X射线相衬成像技术在普通实验室应用和医学肿瘤检测等方面的应用进展。     

临床X射线相衬成像的实现

目的提高人体软组织成像的衬度分辨率及空间分辨率,实现其在临床诊断方面的应用。方法在物理上采用相衬观察法,即附加一些光学装置和某些其他特定条件将相位分布转换成强度分布。而在数学上,则通过傅立叶变换和卷积处理得到其强度分布的数学表达式。结果类同轴全息X射线相衬成像是极有可能应用于临床的一种相位成像方法,并具有广阔的应用前景。结论实现临床X射线相衬成像需要解决相干光源和光源与样品之间及样品与探测器之间距离这样的两个关键技术问题。     

硬X射线相衬成像用于医学临床的物理基础

目的:相较传统X射线医学成像只是利用物体对X射线的吸收不同成像,硬X射线相衬成像利用X射线透过物体时的位相信息成像技术,本文对硬x射线相衬成像能用于医学临床的物理基础作了详细的分析.方法:从麦克斯韦方程出发且只考虑前向散射的情况下推出X射线传播的复折射率表达式.从原子的观点将复折射率同原子的相移与吸收横截面联系起来.结果:从对于不同的X射线能量下,原子相移横截面P及吸收横截面μ与原子序数的关系图、由轻元素及分子的相移及吸收项的关系图分析比较知,对于原子序数较低的原子p/μ的比值约在103的范围,因此位相信息能有效作为衬度来源,其灵敏性对于基于轻元素的软组织更是大大提高,而且随着能量的增大P与μ均减少,但P减少速度慢于μ.在低能量的情况下,相移项δ和吸收项β有同样的数量级,但随着能量的增加,β迅速下降,也即意味着对于这些以轻元素为基的物体若用传统成像法所得吸收相衬像衬度的降低.在高能量区域,δ比β高几个数量级,对于大多数材料,δ约为(103～105)β,在吸收对比度很小的情况下,相衬成像是有可能的.在X射线能量是15 keV～25 keV时生物软组织的吸收项比相移项小很多,硬X射线能强烈的穿透基于轻元素的材料诸如生物软组织.结论:当空间相干X射线束通过生物软组织时,入射波前的相位会随着软组织中电子密度的变化而变化,结果导致了传输方向的微小改变,对于临床医学中较低密度的组织而言,用硬X射线相衬的成像方法将获得传统方法所不能获得的信息.     

不同软组织衍射增强图像的比较研究

我们着重于衍射增强成像(DEI)中的图像及其衬度分析,确定不同组织类型对DEI成像的影响.利用北京同步辐射装置4W1A束线上的形貌与成像站获得三种软组织的衍射增强图像,采用像素-像素的"加"或"减"算法得到表观吸收图像和折射图像,并用衬度分析法对DEI中的峰位图像、表观吸收图像和折射图像的成像质量进行比较.结果显示:软组织的峰位图像与表观吸收图像的吸收衬度相近,但边界效应不及折射图像.不同软组织折射图像的折射衬度不完全相同,肺组织和肾组织的吸收衬度和折射衬度比较高,而肝脏组织的衬度比较低,说明衍射增强成像对改善肝脏组织的成像效果不够明显.因此,折射图像辨别能力强,更适合观察肺和肾等软组织的细微结构.     

生物组织对X射线的折射率因子

目的：传统X射线医学成像是利用X光透过物体时的吸收不同而成像，即只考虑了X光波的强度衰减信息，而忽略X光波的相位变化信息。为提高成像分辨率，利用X光波的相位信息，可以实现相衬成像新技术，以进一步区分不同软组织之间的差别。事实上，X光与物质相互作用时强度的衰减与相位的变化均与物体的折射率有关。本文旨在通过讨论X射线对生物组织的折射率的实部和虚部所包含的物理意义，分析比较了对于通常生物组织X射线通过时吸收与相位改变的大小。方法：基于X光属于电磁波这一性质，借助X光的电磁理论，从微观层次上考虑X光与物质相互作用的过程和细节。为简单起见．先分别考虑了n个原子中的电子和原子核对X光的散射效应，然后综合计及生物活细胞中k种不同组分的物质对X光的散射效应的总和，以得到接近实际的吸收项与相位项。结果：给出了不均匀介质中线性吸收系数和空间位置不同引起的相位改变量的表达式；导出了复折射率的表达式，得到了实数折射率和虚数折射率与原子散射因子的关系；分析比较了含有不同组份的生物组织的相位项与吸收项的大小。结论：物质对X光的吸收与相位变化与物质折射率的实部与虚部有关，根据导出的复折射率的结果，表明X射线与生物组织相互作用时，其相位改变项要远大于吸收项。一般情况下，X射线能量在10keV-100keV之间时，相位项6大约是吸收项卢的1000倍。因此．利用相衬成像技术．可以得到比传统X光吸收成像清晰度高得多的相位衬度图像。     

X射线相位衬度成像的研究进展

在临床医学和材料科学等领域,基于吸收衬度的X射线成像技术是一种非常重要的诊断工具.然而,对于生物医学软组织、聚合物或纤维材料等,由于它们对X射线的弱吸收,这种传统X射线成像技术的应用受到了限制.相位衬度成像是目前X射线成像领域的最新前沿技术和研究热点之一,它能检测对X射线弱吸收的轻元素物质,空间分辨率可达微米甚至亚微米量级,与传统X射线吸收成像技术相比具有独特的优势,并且在医学、生物学、材料科学等领域上获得了成功.介绍了X射线相位衬度成像的原理、成像特点和应用情况.     

基于衍射增强成像的肝纤维化图像多参数纹理特征分析

目的根据硬X射线衍射增强成像工作原理,利用其图像的空间高分辨率和高相位衬度特征,对实验所获得的大鼠正常肝图像及肝纤维化图像进行纹理特征分析,探求其微观结构变化,为计算机辅助诊断提供新手段。方法本次实验在北京同步辐射装置（BSRF）4W/1A光束线形貌站完成,样品为离体大鼠正常肝及由人血白蛋白诱导的免疫损伤性肝纤维化标本,记录介质为FujiIX80胶片。本文计算了感兴趣区域图像的纹理特征参数,以及计算同一类型不同纹理参数间的相关系数,对纹理参数的波动趋势进行了初步分析。结果结果表明,正常及肝纤维化组织在相衬图像上差异较明显,可以通过逆差距、惯量、差的均值以及差的熵这四种纹理参数区分开,其中,后三种纹理参数的波动趋势类似,与逆差距正好相反。结论基于硬X射线衍射增强原理的肝纤维化图像可以通过分析纹理特征来识别其病变,可以用于辅助医生诊断。     

双能量X线荧光数字直接成像系统及图像分离技术的实现

通过计算机主机控制 X线管电压调整、滤线板切换和图像拍摄 ,采用 2 m m铜板过滤高能 X线 ,较好地实现了高、低能量 X线能谱的分离 ,以“双千伏技术”实现了双能量 X线数字成像 ,能够在 2～ 3s内获得高、低能 X线图像 ,基本克服了两幅图像间的运动伪迹。采用简化的双能量图像分离技术获得了胸部软组织图像     

硬X射线相衬成像在裸鼠肿瘤成像方面的研究

传统x射线对软组织的成像是目前的技术弱点.硬x射线是用x射线穿过物体后,x射线的相位改变作为成像因子,它对软组织有较好的成像效果.本课题用硬x射线成像对肝肿瘤组织和胃肿瘤组织进行成像.将25 μl HCT-8人结肠癌细胞移植在裸鼠肝脏上,分别在3 d、4 d、5 d和6 d处死裸鼠,取出肝脏.用同样的方法培养裸鼠早期胃肿瘤,并在3 d和4 d后取出裸鼠胃.对标本进行硬x射线的成像方法即类同轴全息法成像.硬x射线可以对裸鼠肝肿瘤和胃肿瘤进行成像,并且图像分辨率在微米数量级,培养6 d的肝肿瘤可见肿瘤组织.也可清晰观察到3 d和4 d的胃肿瘤.硬x射线成像原理是一个用相位改变因子成像的模式,它的成像对微小物体有着微米级的图像分辨率,是影像学从宏观成像到微观成像的关键,对发现早期的病变组织有明显的优势.     

Multiple-image radiography for human soft tissue

Conventional radiography only provides a measure of the X-ray attenuation caused by an object; thus, it is insensitive to other inherent informative effects, such as refraction. Furthermore, conventional radiographs are degraded by X-ray scatter that can obscure important details of the object being imaged. The novel X-ray technology diffraction-enhanced imaging (DEI) has recently allowed the visualization of nearly scatter-free images displaying both attenuation and refraction properties. A new method termed multiple-image radiography (MIR) is a significant improvement over DEI, corrects errors in DEI, is more robust to noise and produces an additional image that is entirely new to medical imaging. This new image, which portrays ultra-small-angle X-ray scattering (USAXS) conveys the presence of microstructure in the object, thus differentiating homogeneous tissues from tissues that are irregular on a scale of micrometres. The aim of this study was to examine the use of MIR for evaluation of soft tissue, and in particular to conduct a preliminary investigation of the USAXS image, which has not previously been used in tissue imaging.     

X-ray diffraction enhanced imaging as a novel method to visualize low-density scaffolds in soft tissue engineering

Scaffold visualization is challenging yet essential to the success of various tissue engineering applications. The aim of this study was to explore the potential of X-ray diffraction enhanced imaging (DEI) as a novel method for the visualization of low density engineered scaffolds in soft tissue. Imaging of the scaffolds made from poly(L-lactide) (PLLA) and chitosan was conducted using synchrotron radiation-based radiography, in-line phase-contrast imaging (in-line PCI), and DEI techniques as well as laboratory-based radiography. Scaffolds were visualized in air, water, and rat muscle tissue. Compared with the images from X-ray radiography and in-line PCI techniques, DEI images more clearly show the structure of the low density scaffold in air and have enhanced image contrast. DEI was the only technique able to visualize scaffolds embedded in unstained muscle tissue; this method could also define the microstructure of muscle tissue in the boundary areas. At a photon energy of 20?KeV, DEI had the capacity to image PLLA/chitosan scaffolds in soft tissue with a sample thickness of up to 4?cm. The DEI technique can be applied at high X-ray energies, thus facilitating lower in vivo radiation doses to tissues during imaging as compared to conventional radiography.     

Radiography of soft tissue of the foot and ankle with diffraction enhanced imaging

Non-calcified tissues, including tendons, ligaments, adipose tissue and cartilage, are not visible, for any practical purposes, with conventional X-ray imaging. Therefore, any pathological changes in these tissues generally necessitate detection through magnetic resonance imaging or ultrasound technology. Until recently the development of an X-ray imaging technique that could detect both bone and soft tissues seemed unrealistic. However, the introduction of diffraction enhanced X-ray imaging (DEI) which is capable of rendering images with absorption, refraction and scatter rejection qualities has allowed detection of specific soft tissues based on small differences in tissue densities. Here we show for the first time that DEI allows high contrast imaging of soft tissues, including ligaments, tendons and adipose tissue, of the human foot and ankle.     

Quantitative comparison of imaging performance of x-ray interferometric imaging and diffraction enhanced imaging

For detailed biomedical observations using the optimum phase-contrast x-ray imaging, quantitative comparisons of imaging performances of two major imaging methods--x-ray interferometric imaging (XII) and diffraction enhanced imaging (DEI)--were performed. Density sensitivity and spatial resolution of each imaging method were evaluated using phantom tomograms obtained by each method with the same x-ray dosage. For practical comparison of the methods, biological samples were also observed under the same conditions. The results show that XII has a higher sensitivity than that of DEI and is thus suitable for observation of soft biological tissues. On the other hand, DEI has a wider dynamic range of density and is thus suitable for observation of samples with large differences in density of different regions.     

应用IQF值评价不同显示器的性能

目的：检测三种显示器的性能,应用图像质量因子（IQF）值定量评价三种显示器用于医学图像显示的效果．评估三种显示器用于医学图像诊断的可行性。方法：使用亮度及照度测量器L100测量显示器的亮度．使用美国医学物理师协会（AAPM）测试图对三种显示器（彩色LED显示器,黑白LED医用显示器,高亮度彩色手机显示屏）的亮度响应进行量化评价并绘出标准的亮度响应曲线。使用对比度细节体模CDRAD2．0图像．通过计算IQF值．评价三种显示器的图像解析能力并使用ANOVA对IQF值进行统计学分析。结果：三种显示器的亮度比均超过了AAPMTGl8的推荐标准,彩色LCD显示器和手机屏对比度响应的测量值都在标准值的±10％范围内,但并不是都完全符合AAPMTGl8文件推荐的标准。黑白LCD显示器与其它两种显示器的IQF值有显著统计学差异,黑白显示器的图像质量较好。结论：亮度响应好的显示器,其成像质量也较好。手机LCD屏虽不能完全满足AAPMTG18文件的要求．但其在显示图像细节方面与彩色LCD显示屏差别甚微。     

CT影像处理技术在脊柱畸形矫形手术设计中的应用价值

目的探讨CT影像处理技术在脊柱畸形矫形手术设计中的应用价值。方法 30例脊柱畸形矫形患者同期行X线片、CT检查,其中CT检查图像处理主要为3D骨重建和3D重建加CTA联合成像。结果 X线平片无法进行动态旋转观察,并且椎管内结构情况不满意。CTA联合成像和3D骨重建在脊柱侧弯的椎体显示方面效果均优于X线平片,重建图像可以旋转任意角度,切除干扰肋骨,从而可以发现脊柱三维空间的畸形。在CT测量的值中,骨桥的CT值最大,正常椎体的CT值最少,各个组织间的CT值多存在显著差异（P〈0.05）。结论 CT影像处理技术在脊柱畸形矫形手术中的应用能在侧弯椎体确认、椎体旋转度测量和椎管显示方面获得很好的效果,同时不同骨组织的CT值也明显不同,从而为手术设计提供了参考。     

Refraction-angle resolution of diffraction enhanced imaging

As a new method, x-ray diffraction enhanced imaging (DEI) has extremely high sensitivity for weakly absorbing low-Z samples in medical and biological fields. Conventional performance parameters, such as spatial resolution and low-contrast resolution, are not enough to describe the characteristics of a DEI system. This paper focuses on refraction-angle resolution which describes the ability of a DEI system to differentiate the x-rays refracted by the sample. The analysis of refraction-angle resolution is composed of two parts: the analysis of the single DEI image measured in a certain position of the rocking curve and the analysis of the refraction-angle image calculated by extraction methods. A 2D computer simulation experiment is performed to prove the results of the analyses. The limitations and conclusions of refraction-angle resolution are described in the end.     

Ultrasonic tissue characterisation and echographic imaging

Acoustic models of soft biological tissues are discussed. The methods to derive acoustic bulk parameters, i.e. attenuation coefficient and backscattering coefficient are outlined. When applying a specific backscattering model the effective dimension of the scattering sites within a tissue can be estimated. The texture of echographic images is defined in terms of speckle and it is discussed in which way the texture is influenced by the beam formation and the volume density of the scatterers. Structural characteristics of tissues are discussed and the method to estimate a structural dimension is indicated. Recent developments are parametric imaging and image processing.