参数对微焦点源相位相衬像质影响的研究

微焦点同轴X射线相位相衬成像能得到清晰度和分辨率高的图像.本文从理论上用计算机模拟的方法分析各参数对成像质量的影响,以指导实验时避免不必要的时间和材料浪费,获得理想的图像.     

X射线相位衬度CT

X射线相位衬度CT指的是在通过X射线光源来对物体进行成像过程中使用图像的位相衬度来反映物体的密度或者厚度分布,适用于弱吸收物体,还可以减少吸收剂量,放宽成像条件中光源强度的限制和减少对样品(尤其是生物样品)的损伤.介绍了目前用于X射线相位衬度CT的三种方法,实验及图像重建的过程,并分析了各自的优缺点.     

快速高能X射线光栅相衬成像

X射线光栅相衬成像对弱吸收物质成像能够获得较高的图像衬度,然而使用高分辨探测器,成像时间长。此外,受光栅工艺限制,成像能量通常在30 keV左右。文中基于投影成像原理,大大放宽了对光栅工艺的要求,提高了成像能量。同时,利用医用CT球管以及医用探测器,基于周步进扫描模式,实现了快速相衬CT成像。在国家同步辐射实验室搭建的成像系统上,完成了80 kV管电压（等效能量约48 keV）180 mA管电流,物体80 s曝光的二维和三维成像实验。针对实验结果,进一步探讨了提高密度分辨率的方法和途径。     

衍射增强成像折射衬度的应用

折射衬度是衍射增强成像(diffraction enhanced imaging,DEI)中的一种重要衬度,在弱吸收物质的成像中,折射衬度远超过吸收衬度.折射衬度应用的关键是提取出样品的折射信息,折射信息由相应的折射图像表示.根据生物样品和材料样品的特点,研究和比较了两种折射信息提取方法.利用样品的折射图像,对聚苯乙烯样品进行了简单的定量分析,比较了正常肝组织和肝血管瘤组织.实验结果表明,折射衬度清楚地描述了肝组织的微细结构和血管瘤损伤,精确地显示了无法在传统X射线成像技术中获得的聚苯乙烯样品的清晰结构.     

相衬技术在现代光学中的应用

相衬技术由于能解决相位到振幅的转换而备受关注。随着近几年对其更进一步的研究,发现相衬技术在图像合成,三元相控阵列照明的重建、光镊技术以及X射线相位衬度成像技术中有着广泛的应用,本文对相衬技术的原理及其在现代光学中的应用做简要介绍。     

PNAS：我国X射线相位衬度成像研究获重大突破 医疗CT技术有望实现新飞跃

中国科学技术大学研究员吴自玉领导的北京同步辐射装置和合肥国家同步辐射实验室联合成像科研小组,在X射线相位衬度成像研究领域取得重大突破,其研究成果克服了医学X射线CT技术应用X射线相位衬度成像方法的障碍,为形成更加快速、灵敏度更高、更安全的X射线相位CT技术奠定了基础。专家预测,这项新技术的诞生。将催生新型X射线相位CT产业。     

硬X射线相位相衬成像研究进展

自从20世纪90年代中叶以来,硬X射线相位相衬成像技术因其对弱吸收材料的极高灵敏度引起了国内外广泛的关注,医学及生物成像是相位相衬成像的主要目标.详细论述了各种相位相衬成像技术的研究进展情况.     

硬X射线相位衬度成像的实验研究

介绍了硬X射线(类同轴)相位衬度成像的工作原理及其实验研究结果。X射线波长为0．08860nm,样品为未经任何处理的飞蛾，记录介质为X射线胶片。胶片经处理以后，用光学显微镜读出，可以看出样品的许多细节,尤其在折射率突变处。而同样条件下基于吸收衬度机制的硬X射线吸收成像，由于是弱吸收样品．没有观察到任何图像。     

X射线光栅相衬成像的仿真

根据菲涅耳衍射积分理论,提出了X射线光栅相衬成像系统的仿真模型。以聚甲基丙烯酸甲酯（PMMA）小球作为成像物体模型,选取30 keV的X射线做模拟计算。通过仿真,得到了穿过球体和相位光栅的X射线波前的变化。采用多步位移法从模拟条纹图中恢复出了PMMA小球的相位信息,并分析了莫尔条纹对比度对成像质量的影响,为实际的实验提供可靠的参数选择。经过仿真得到的相移信息与通过实验得到一致,验证了仿真算法的正确性。     

整形脉冲信号处理方法及低温辐射流偏差

平响应X射线二极管目前已经广泛应用在国内外大型激光装置,用于角分布X射线辐射流的测量。在实际实验中,平响应X射线二极管会对整形脉冲驱动辐射源产生台阶变化的辐射流图像进行测量。为了保证信噪比良好,单一信号会接入示波器多通道,然后对不同通道信号进行数据处理,并且拼接得到最后信噪比很好的图像。该研究主要对这种数据处理方式进行了介绍,并给出了理论计算,同时对低温辐射流还原计算中的一种偏差做了理论近似和数值模拟,得到了偏差的相对不确定度。耦合所有因素的不确定度,得到了平响应X射线二极管的整体不确定度随辐射温度的变化曲线,实现了精密化诊断,完成了实验对于诊断的需求。     

Sensitivity of photon-counting based K-edge imaging in X-ray computed tomography

The feasibility of K-edge imaging using energy-resolved, photon-counting transmission measurements in X-ray computed tomography (CT) has been demonstrated by simulations and experiments. The method is based on probing the discontinuities of the attenuation coefficient of heavy elements above and below the K-edge energy by using energy-sensitive, photon counting X-ray detectors. In this paper, we investigate the dependence of the sensitivity of K-edge imaging on the atomic number Z of the contrast material, on the object diameter D , on the spectral response of the X-ray detector and on the X-ray tube voltage. We assume a photon-counting detector equipped with six adjustable energy thresholds. Physical effects leading to a degradation of the energy resolution of the detector are taken into account using the concept of a spectral response function R(E,U) for which we assume four different models. As a validation of our analytical considerations and in order to investigate the influence of elliptically shaped phantoms, we provide CT simulations of an anthropomorphic Forbild-Abdomen phantom containing a gold-contrast agent. The dependence on the values of the energy thresholds is taken into account by optimizing the achievable signal-to-noise ratios (SNR) with respect to the threshold values. We find that for a given X-ray spectrum and object size the SNR in the heavy element's basis material image peaks for a certain atomic number Z. The dependence of the SNR in the high- Z basis-material image on the object diameter is the natural, exponential decrease with particularly deteriorating effects in the case where the attenuation from the object itself causes a total signal loss below the K-edge. The influence of the energy-response of the detector is very important. We observed that the optimal SNR values obtained with an ideal detector and with a CdTe pixel detector whose response, showing significant tailing, has been determined at a synchrotron differ by factors of about two to three. The potentially very important impact of scattered X-ray radiation and pulse pile-up occurring at high photon rates on the sensitivity of the technique is qualitatively discussed.     

基于CMOS图像传感器的微光成像系统信噪比研究

信噪比是微光成像系统的关键参数,决定了成像系统的性能与成像质量。给出了互补金属氧化物半导体（Complementary Metal Oxide Semiconductor, CMOS）图像传感器微光成像系统的信噪比模型,仿真计算了系统的信噪比与信号、噪声的关系。搭建了信噪比测试环境,完成了系统信噪比测试实验。实验结果表明,理论值与实测值一致。最后,根据信噪比分析结果对给定系统进行了参数优化。计算结果显示,优化后的系统在1 mLux照度下,信噪比能达到4.5。信噪比的研究为基于CMOS微光成像系统的总体设计与优化提供了理论依据。     

Fabrication of High-Aspect Ratio Nanogratings for Phase-Based X-Ray Imaging

Diffractive optical elements such as periodic gratings are fundamental devices in X-ray imaging – a technique that medical, material science, and security scans rely upon. Fabrication of such structures with high aspect ratios at the nanoscale creates opportunities to further advance such applications, especially in terms of relaxing X-ray source coherence requirements. This is because typical grating-based X-ray phase imaging techniques (e.g., Talbot self-imaging) require a coherence length of at least one grating period and ideally longer. In this paper, the fabrication challenges in achieving high-aspect ratio nanogratings filled with gold are addressed by a combination of laser interference and nanoimprint lithography, physical vapor deposition, metal assisted chemical etching (MACE), and electroplating. This relatively simple and cost-efficient approach is unlocked by an innovative post-MACE drying step with hexamethyldisilazane, which effectively minimizes the stiction of the nanostructures. The theoretical limits of the approach are discussed and, experimentally, X-ray nanogratings with aspect ratios >40 are demonstrated. Finally, their excellent diffractive abilities are shown when exposed to a hard (12.2 keV) monochromatic X-ray beam at a synchrotron facility, and thus potential applicability in phase-based X-ray imaging.     

Preliminary feasibility study of an in-line phase contrast X-ray imaging prototype

In this study, a series of imaging experiments on biological specimens, including human breast core biopsies, lumpectomy, and chicken tissues, as well as standard phantoms, were performed in an effort to investigate the feasibility of an in-line phase contrast X-ray imaging prototype. The prototype system employed in the study consists of a microfocus X-ray source with tungsten target and a digital flat panel detector, and it can be operated in both conventional attenuation-based imaging mode and in-line phase contrast imaging mode. Biological specimens were imaged in the conventional mode and phase contrast mode with the same source-to-image-detector distance (SID), and phase contrast images exhibited both improved image quality compared with conventional images, and the overshooting patterns along the boundaries in the specimens, which revealed the occurrence of the edge enhancement effect provided by the phase contrast technique. In addition, the performance of the phase contrast mode and conventional mode was compared based on the American College of Radiology (ACR) phantom imaging and contrast detail mammography (CDMAM) phantom-based contrast detail analysis with two experimental settings: one with the same SID and the other with the same object entrance exposure. In both pairs of comparison under our experimental conditions, the phase contrast imaging mode exhibited improved image quality as compared to the conventional mode, which further supported the feasibility of the prototype.      

X-Ray Characterization of Low-Thermal-Conductivity Thin-Film Materials

X-ray diffraction and imaging techniques at the Advanced Photon Source (APS) have been used to characterize PbSe/MoSe₂ and PbSe/WSe₂ thin films and multilayers. Diffraction measurements with area detectors were made to demonstrate the nanoscale coherence size of the layers both in-plane and perpendicular to the surface. Higher-resolution diffraction measurements that exploit the tunability of synchrotron radiation for anomalous scattering contrast have been used to accurately determine layer spacings in these multilayers. We also discuss opportunities in other new and emerging x-ray techniques, such as time-resolved studies during growth or processing, and present x-ray imaging capabilities that can be used to investigate thermoelectric thin-film materials.     

结构简单的X射线二极管及其性能指标测定

研制了一种可用于测量软X光辐射的X射线二极管(XRD).该XRD具有结构简单、对偏压及真空度要求较低、响应面积大等特点.分析了 XRD的响应时间和饱和电流等特性,给出了能量计算公式,同时采用同步辐射光源对XRD进行了能壁标定,标定结果与理论计算结果一致.利用该XRD对毛细管放电类氖氩46.9 nm激光脉宽和能量进行了测量.     

微波设备表面电磁泄漏位置检测方法研究

针对微波设备表面电磁泄漏位置的检测方法进行研究,根据其表面等效辐射源形式的不同,设计了不同的检测方法,并提出了相应的实验测试方案.其中,综合孔径被动辐射计成像的方法适用于表面等效辐射源为非相干源的情况;数字透镜相移成像的方法适用于表面等效辐射源为相干源的情况;物理透镜成像的方法适用于表面等效辐射源为非相干源、相干源和部分相干源的全部三种情况.     

对基于拼接干涉术的同步辐射镜测量技术的研究

随着同步辐射光源和自由电子激光器相关技术的发展和光束质量的提升,对用于转递和聚焦光束能量的X光反射镜的指标要求也逐渐提高。为避免引入额外的波前误差,反射镜面形高度误差均方根值的要求已逼近至亚纳米量级。如此苛刻的面形要求对X光反射镜的测量工作带来了极大的困难和挑战。除了在各国同步辐射光源得到广泛使用的长程轮廓仪等基于角度测量的轮廓扫描仪器之外,基于激光干涉仪的拼接干涉技术也发展为测量同步辐射镜的一种有效手段。文中主要介绍了近期笔者等为测量X光反射镜而开发的拼接干涉平台。利用这一测量平台,研究了在不同的拼接参数下的多种拼接模式。着重讲述了其中纯软件拼接模式的基本原理和实际测量。用实测结果与不同测量仪器和不同研究机构的结果进行比对,验证了拼接干涉测量用于检测同步辐射镜的有效性,并展示了此拼接平台的测量表现。根据所得的测量数据看来,使用纯软件拼接模式来测量X光平面反射镜时,测量重复性的均方差值可以达到0.1 nm左右;而测量X光双曲柱面镜时(曲率半径的变化范围为50~130 m),测量重复性的均方差值为0.2~0.3 nm。此结果基本满足平面和接近平面(曲率半径大于50 m)的同步辐射镜常规检测和为确定性加工提供面形反馈的需要。