同步辐射硬X射线微束技术

同步辐射硬X射线微束(微探针)技术是目前很多学科领域的主流分析技术,本文介绍了同步辐射硬X射线的各种微束技术以及微束的应用研究情况,阐述了各种微束技术的基本聚焦原理,并对其优势和不足以及发展状况作了简要的概述.     

镍基合金受熔融氟化盐腐蚀的同步辐射XRF分析

采用浸入法在750℃熔融氟化盐(LiNaK-F)中进行Inconel 600、Hastelloy X、Hastelloy c-276镍基高温耐蚀合金的腐蚀实验.利用同步辐射微束X射线荧光分析(μ-XRF)及X射线衍射(XRD)对样品进行了分析测试.μ-XRF结果表明,镍基合金在熔融氟化物中的腐蚀主要为合金元素Cr的流失...     

用同步辐射共聚焦X射线方法研究古代彩绘样品的层状结构

同步辐射共聚焦X射线方法是一种元素成分及其化学结构的三维无损分析方法,在地质、考古、环境、生物及材料等领域具有重要的应用。在上海光源的硬X射线微聚焦光束线站(BL15U)建立共聚焦X射线实验方法,并用于故宫彩绘样品的制作工艺及层状结构分析。基于BL15U的K-B聚焦系统,在能散探测器前采用会聚毛细管半透镜实现与K-B聚焦镜焦点的共聚焦状态,深度分辨在8.04 ke V(Cu-Kα)为31.5μm,可以开展共聚焦微束X射线荧光(Micro-X-ray Fluorescence,Micro-XRF)和共聚焦微束X射线吸收精细结构(Micro-X-ray Absorption Fine Structure,Micro-XAFS)实验研究。对故宫斗彩陶瓷和彩绘样品进行了元素及其化学态的深度分布分析,获得了斗彩陶瓷特有的三层釉结构以及彩绘样品内部颜料的化学信息。实验结果表明,该系统具有较高的空间分辨和探测灵敏度,是文物样品三维无损分析的有力工具。     

北京同步辐射X—射线荧光微束分析进展

论介绍了北京同步辐射X－射线荧光微束分析装置的最新进展,以及近年来在生物医学和石油地质领域的应用研究工作,重点报导了前不久在国内首次使用该方法,对单个流体包裹体探测的实验结果。     

同步辐射微束X射线荧光分析及其在生物医学中的应用

介绍了同步辐射微束X射线荧光分析的特点，主要的仪器设备和方法。介绍了在头发和病变组织中微量元素成分的扫描分析，细胞元素谱及其在外界物理、化学条件下的变化分析等。展示了同步辐射微束X射线荧光分析在生物医学研究中的广阔前景。     

具有加速因子的OSEM重建算法用于X射线荧光CT研究

有序子集最大期望值算法(Ordered Subsets Expectation Maximization,OSEM)具有较高的图像重建质量和较短的计算时间,已经被应用于内源CT(如SPECT、PET、同步辐射X射线荧光CT)的图像重建中。本文提出了一种具有加速因子的OSEM算法应用于X射线荧光CT的图像重建,通过引入加速因子h来调制校正因子的步长加快OSEM算法的收敛速度,研究了不同加速因子和不同子集数的AOSEM算法对重建图像质量的影响。计算机模拟及实验结果表明,在获得同等质量重建图像的同时,具有加速因子的OSEM算法的重建速度是常规OSEM的两倍。     

同步辐射研究单个藻细胞对金属元素的摄取性能

本介绍了用同步辐射微束X射线荧光法对单个藻细胞的研究方法，在北京同步辐射荧光站上首次实现了单细胞水平的测量。报道了单个藻细胞摄取金属离子前后细胞内元素含量的变化。     

双能量X射线荧光全息图重构算法消除孪生像的模拟研究

X射线荧光全息术以样品内部的发光原子作为相干光源进行全息成像,可以直接观测到晶体内部原子的三维排列结构.和传统的全息术一样,X射线荧光全息术也遇到了孪生像问题.本文以27个Fe原子成立方排列的结构为模型,采用双能量荧光全息图重构算法研究入射X射线能量的选取对消除孪生像效果的影响.结果表明:记录荧光全息图的两个X射线能量越接近(对于内探测器全息术而言,最小能量差取决于单色器和探测器的能量分辨率;对于内源全息术而言,最小的能量差取决于元素的两个紧邻荧光能量差和探测器的能量分辨率),消除孪生像的效果越好;而入射X射线的能量越高,则原子像的分辨率越高.     

上海光源BL15U1束线的SRXRF定量分析

本文介绍了用于同步辐射X射线荧光(XRF)定量分析的基本参数法(FP)和MC模拟法。上海光源(SSRF)硬X射线微聚焦光束线(BL15U1)应用上述两种方法对样品进行定量分析,验证了方法的有效性并用定量分析结果计算了BL15U1光束线部分元素的荧光探测限。实验结果表明,对样品中μg/g量级元素含量的定量分析结果相对误差都在10%以内,而使用MC模拟法可以直观地比较不同参数下的模拟谱与实验谱,辅助实验参数的确定,从而减小参数引起的误差,得到更为准确的结果。此外,对BL15U1探测限的计算表明该光束线具备开展高性能荧光实验的能力。     

微束X射线荧光无损分析古瓷器高铅釉的方法及应用研究

研究了微会聚透镜分析高铅样品的特征,采用基于微会聚透镜的微束X射线荧光无损定量分析了一片清代彩绘瓷彩料中的元素含量,同时扫描分析了彩料中某一特定区域的元素分布。从元素分布中可推测出清代彩绘的制作工艺是先用高铅的Mn颜料绘出图案的轮廓,然后向中间填充设计好高铅的Cu颜料,或直接用高铅的Fe混合物绘画。分析结果表明,基于微会聚透镜的微束X射线荧光分析是一种较好的高铅样品的分析手段。     

若干因素对同步辐射微束X射线荧光 CT图像质量的影响研究

借助计算机模拟成像，通过分析不同情况下的图像重构，研究了抽样间距和投影数、重构算法、荧光测量等若干因素对图像重构质量的影响，并得出了一些有益的结果，对实际应用具有一定的参考意义。     

基于SART算法的CL硬化伪影校正方法研究

X射线薄板层析成像(CL)系统是一种针对板状构件的新型断层成像系统,该系统中存在射束硬化现象。本工作研究了一种基于SART算法的硬化伪影校正算法（SART-BHC算法）,通过对该算法的研究及对CL系统矩阵的计算,使该方法能应用于CL中。通过模拟与实验相结合的方式,利用蒙特卡罗方法获得CL投影的模拟数据,在实际CL中获得实验数据,然后利用SART-BHC与FPB算法对两种数据分别重建。结果表明,SART-BHC算法可应用于CL中,不需要任何先验知识,能很好地校正硬化伪影,并对层间混叠有抑制作用。     

裂变位垒参数子库（CENPL－FBP－1）的管理－检索程序系统

描述了中国评价核参数库的１个子库──裂变位垒参数库的管理－检索程序系统，介绍了其特点、功能和用法。     

基于蒙特卡罗模拟3-DPET图像重建的研究

应用蒙特卡罗模拟软件GATE对GeDiscoveryLSPET/CT扫描系统进行模拟,获得三维投影数据,分别采用三维有序子集最大期望值法（3-DOSEM）与三维滤波反投影法（3-DFBP）进行图像重建,从空间分辨率、成像的对比度以及信噪比等方面对3-DOSEM法与3-DFBP法的重建结果进行比较。结果显示,对蒙特卡罗方法模拟获得的三维投影数据,采用3-DOSEM法重建比3-DFBP法重建得到的图像质量好。     

SPECT/CT活度定量中校准体模和重建方法的选择

本文探讨了SPECT/CT校准体模和重建方法的选择,以用于临床SPECT/CT的准确活度定量。分别对活度已知的点源、大圆柱、小圆柱3种校准体模进行SPECT/CT扫描,然后对每个断层数据依次采用4种重建方法（FBP、OSEM、OSEM+AC、OSEM+AC+SC）进行重建,并据此计算校准因子。将小圆柱作为活度定量的对象进行定量误差计算。OSEM+AC和OSEM+AC+SC的平均相对定量误差均小于10%,FBP和OSEM的平均相对定量误差均大于20%。OSEM+AC的平均相对定量误差在采用小圆柱做校准体模时与OSEM+AC+SC无显著差异,而在采用大圆柱和点源时,分别较OSEM+AC+SC的小3.38%和6.48%（P<0.05）。3种体模的对比中,采用OSEM+AC时差异不显著,采用其他重建方法时差异显著。采用OSEM+AC+SC时,小圆柱作校准体模的定量误差较大圆柱和点源的结果分别小3.92%和6.42%（P<0.05）。结果表明,基于CT和迭代算法的衰减校正可有效提升活度定量准确性,但散射校正的效果不佳;校准体模应尽可能与目标定量对象相似。合理选择校准体模和重建方法,可有效提升SPECT/CT的活度定量准确性。     

利用旋转极坐标法提高CT重建速度

图像重建速度是评判CT重建算法的一个重要性能指标.对CT重建区域按照极坐标进行划分,改进了传统卷积反投影(FBP)重建算法的流程,极大的提高了图像重建的速度.     

Comparison of Hotelling observer models and human observers indefect detection from myocardial SPECT imaging

The objective of this study was to compare defect detection performance using a channelized Hotelling observer with radially symmetric channel (RSC) and oriented channels (OC) to that found in a previously reported human observer ROC study (see K.J. LaCroix and B.M.W. Tsui, “An evaluation ofthe effect of nonuniform attenuation compensation on defect detection for Tc-99m myocardial SPECT images,” J. Nucl. Med., vol. 38, p. 19P, 1997). The observer's task involved the detection of left-ventricular myocardial perfusion defects for Tc-99m sestamibi myocardial perfusion SPECT images. The images were reconstructed using the filtered-backprojection (FBP) algorithm without attenuation compensation or the maximum-likelihood expectation-maximization (ML-EM) algorithm with non-uniform attenuation compensation (AC). This was performed for cases with and without significant attenuation artifacts. The areas under the ROC curves for the Hotelling observers were calculated and compared to those for the human observers. The ML-EM reconstructed images (with AC) had high defect detectability across all anatomy types, while with FBP, a lower detectability was found for cases where the reconstructed images contained attenuation artifacts in the myocardium. Similar trends between the channelized Hotelling observer and those from the human observer study were found with both radially symmetric channel (RSC) and oriented-channel (OC) models. Further investigation of the channel models is needed to determine the number and alignment of orientations and the number and cutoff of frequency bands to improve agreement between human and Hotelling observer results     

Range Condition and ML-EM Checkerboard Artifacts

The expectation maximization (EM) algorithm for the maximum likelihood (ML) image reconstruction criterion generates severe checkerboard artifacts in the presence of noise. A classical remedy is to impose an a priori constraint for a penalized ML or maximum a posteriori probability solution. The penalty reduces the checkerboard artifacts and also introduces uncertainty because a priori information is usually unknown in clinic. Recent theoretical investigation reveals that the noise can be divided into two components: one is called null-space noise and the other is range-space noise. The null-space noise can be numerically estimated using filtered backprojection (FBP) algorithm. By the FBP algorithm, the null-space noise annihilates in the reconstruction while the range-space noise propagates into the reconstructed image. The aim of this work is to investigate the relation between the null-space noise and the checkerboard artifacts in the ML-EM reconstruction from noisy projection data. Our study suggests that removing the null-space noise from the projection data could improve the signal-to-noise ratio of the projection data and, therefore, reduce the checkerboard artifacts in the ML-EM reconstructed images. This study reveals an in-depth understanding of the different noise propagations in analytical and iterative image reconstructions, which may be useful to single photon emission computed tomography, where the noise has been a major factor for image degradation. The reduction of the ML-EM checkerboard artifacts by removing the null-space noise avoids the uncertainty of using a priori penalty.     

Practical use of the modified Bronnikov algorithm in micro-CT

Through the years, the resolution of X-ray Computed Tomography (CT) systems has increased rapidly, in particular for the newer micro- and nano-CT systems. With this increasing resolution, the limits of absorption contrast CT are being reached. At the same time, a new type of contrast becomes visible: phase contrast. Mainly for low-absorbing objects such as insects and wood, phase contrast can lead to a new type of CT reconstruction using the modified Bronnikov algorithm (MBA) [A. Groso, R. Abela, M. Stampanoni, Implementation of a fast method for high 297 resolution phase contrast tomography, Opt. Express 14 (18) (2006) 8103.] Despite it’s theoretical limitation to pure phase objects, the algorithm has some clear advantages with respect to filtered back-projection (FBP). The MBA is therefore commonly used at the Centre for X-ray Tomography of the Ghent University (UGCT) to obtain additional information for optimal scanning results.     

Improvements to conventional X-ray tube-based cone-beam computed tomography system

Conventional X-ray tube-based cone-beam computed tomography(CX-CBCT) systems have great potential in industrial applications. Such systems can rapidly obtain a three-dimensional(3D) image of an object.Conventional X-ray tubes fulfill the requirements for industrial applications, because of their high tube voltage and power. Continuous improvements have been made to CX-CBCT systems, such as imaging time shortening,acquisition strategy optimization, and imaging software development, etc. In this study, a CX-CBCT system is developed. Additionally, some improvements to the CX-CBCT system are proposed based on the hardware conditions of the X-ray tube and detector. A near-detector(ND)geometry condition is employed to obtain a sharper image and larger detection area. An improved acquisition strategy is proposed to simplify operations and reduce total imaging time. In the ND geometry condition, a simplified method called FBP slice stacking(SS-FBP) is proposed, which can be applied to 3D image reconstruction. SS-FBP is timesaving relative to traditional methods. Furthermore, imaging software for the CX-CBCT system is developed in the MATLAB environment. Several imaging experiments were performed. The results suggest that the CX-CBCT system works properly, and that the above improvements are feasible and practical.