Measurement of spatial resolution of the micro-CT system

The performance test is an important and necessary work for the micro-CT （computed tomography） system. The focal spot size of the micro focus X-ray tube is measured. The method of measuring the spatial resolution of micro-CT is introduced. A line-pair resolution of 28.2 lp/mm at the 10% modulation transfer function （MTF） level can be achieved with 14.7 μm spot size, 12.3 μm voxel size and a 25 mm field of view. In addition, a tungsten wire with the diameter of 5 μm can be detected by the system.     

辐射照相系统中转换屏的分辨率研究

 在高能X光辐射照相系统中，通常使用闪烁体材料的转换屏将X光转换为可见光进行探测。建立了转换屏空间分辨率的计算模型，模拟了转换屏的空间分辨率随屏的厚度、材料及X光子能量的变化关系，为系统的设计提供了参数。     

双近贴聚焦微光像增强器分辨力理论极限问题研究

分辨力和MTF是微光像增强器的2个重要参数。根据线性系统傅里叶频谱理论,分析了微光像增强器的MTF和分辨力特性。 计算出理想条件下,基于光阴极/MCP/荧光屏3部件结构以及带内电子增益机制的光阴极/荧光屏2部件结构的近贴聚焦像管的理论极限分辨力。它们分别是96.6lp/mm和98.1lp/mm。该结果可供人们改进像管MTF及分辨力特性时参考。     

分幅变像管动态空间分辨率的标定

为了提高激光惯性约束聚变实验二维成像诊断的精密化程度, 提出了分幅变像管动态空间分辨率的标定方法. 标定原理是以直边函数为物, 经光学系统成像后求解系统的调制传递函数, 从而获得系统的空间分辨率. 在神光Ⅱ装置上利用八路激光打靶产生1-3.5 keV能区的连续X 射线标定源, 照射高Z刀边材料, 并成像到分幅变像管阴极上, 分幅变像管采用脉冲选通工作模式获得动态像. 对分幅变像管采集的动态图像进行处理得到系统的调制传递函数. 根据调制传递函数为0.1时对应的空间截止频率, 得到系统的空间分辨率为20 lp/mm. 根据分幅变像管的动态空间分辨理论, 计算系统的极限空间分辨率为22.8 lp/mm. 标定结果略低于极限空间分辨率, 与理论基本吻合. 根据传统标定方法得到该分幅变像管的静态空间分辨率为22 lp/mm, 比动态空间分辨率略高. 在二维成像诊断时, 分幅变像管工作于动态选通模式, 故动态空间分辨率的标定结果更能真实地反映其成像诊断能力.     

中子半影成像的闪烁体阵列空间分辨力模拟

为了比较3种闪烁体探测器的性能,利用蒙特卡罗方法计算了不同光纤直径的闪烁体阵列的空间分辨和能量沉积。模拟结果表明:相同光纤直径的普通液体闪烁体阵列空间分辨力比塑料闪烁体阵列提高了约0.1 mm,而氘代液体闪烁体阵列空间分辨力约为普通液体闪烁体阵列的1/2;富氢闪烁体的能量沉积比氘代闪烁体高;闪烁体光纤直径越小,分辨力越好;闪烁体越厚,光产额越高。     

三代微光像增强器分辨力计算理论模型

分辨力和传递函数MTF是微光像增强器的2个重要参数。长期以来，人们对于三代微光像增强器阴极发出的电子初能量分布没有统一的认识，从而没有一个公认的分辨力和MTF计算模型。通过理论分析和假设，给出一定条件下一个分辨力计算模型。把实际测得的第一近贴距、第二近贴距、阴极电压和荧光屏电压等数值代入分辨力计算模型中，可以得到分辨力理论值。经与实际测量值进行比对，发现二者偏差值在12.3%以内，此理论模型基本符合实际需求。该分析方法和所得结果有一定实用价值，可作为设计三代微光像增强器的技术参考。     

Measurement of the spatial resolution and the relative density resolution in an industrial cone-beam micro computed tomography system

The spatial resolution and the relative density resolution are the two most critical indicators in CT system. The method recommended in the ASTM E1695-95 and GJB 5311-2004 is only suitable to the fan-beam CT system. In this paper, for industrial cone-beam micro CT system, we will adopt the edge response function (ERF) created by the step edges of a steel ball to measure the system 3D PSF and MTF. To describe the contrast discrimination function more accurately, we will first propose to extend the two-dimensional measurement region to the three-dimensional space. Our experimental spatial resolution is (55.56±0.56) lp/mm and the relative density resolution is 1% within 300 μm×300 μm×300 μm according to the 3σ rule.     

The measurement of the electrical field distribution by external electro-optic measuring system with submicrometre spatial resolution

A GaAs solid immersion lens has been applied to the external electric-optic measuring system. The spatial resolution of the system is improved to 0.7 μm because of the increased effective number aperture. We measured the electrical field distribution of ceramic microstrip lines transversely. The variation of electrical field with a submicrometre interval has been revealed experimentally and the results are in good agreement with the theoretical analysis.     

Research of spatial resolution in external electro-optic probing

A new method, based on zero point of longitudinal electric field, was used to determine the spatial resolution of external electro-optic (EO) probing equipment. Considering the diffraction of Gauss beam, the result of external EO probing was simulated which was in accordance with the experiment. A spatial resolution <1 μm was demonstrated initially in our equipment using 650 nm laser diode as probe beam and semi-insulating GaP as probe tip.     

Beam hardening correction for a cone-beam CT system and its effect on spatial resolution

In this paper, we present a beam hardening correction (BHC) method in three-dimension space for a cone-beam computed tomography (CBCT) system in a mono-material case and investigate its effect on the spatial resolution. Due to the polychromatic character of the X-ray spectrum used, cupping and streak artifacts called beam hardening artifacts arise in the reconstructed CT images, causing reduced image quality. In addition, enhanced edges are introduced in the reconstructed CT images because of the beam hardening effect. The spatial resolution of the CBCT system is calculated from the edge response function (ERF) on different planes in space. Thus, in the CT images with beam hardening artifacts, enhanced ERFs will be extracted to calculate the modulation transfer function (MTF), obtaining a better spatial resolution that deviates from the real value. Reasonable spatial resolution can be obtained after reducing the artifacts. The 10% MTF value and the full width at half maximum (FWHM) of the point spread function with and without BHC are presented.     

微扫描对空间分辨率的影响

在详细分析使用微扫描技术减少混淆效应的基础上，给出一种利用微扫描技术进行空间分辨率影响分析的像素传递函数（PTF）方法，并基于2×2和4×4两种微扫描形式对该函数进行分析计算和讨论。计算结果表明，在焦平面阵列给定的情况下，微扫描技术能适当提高焦平面空间的分辨率，有效减小图像混淆，明显改善成像质量。指出在没有高空间分辨率成像器件的情况下，利用微扫描技术和低分辨率成像器件来获得较高空间分辨率的图像是完全可能的。     

一种提高CCD像元分辨率方法的初步探讨

提出了一种面阵CCD成像的对角钱错位合成方法。该方法将两幅沿对角线方向错位拍摄的CCD图像迭加成一幅合成的图像。给出了两种合成计算公式 ,并分析讨论了合成图像的空间分辨率。分析表明 ,此种方法能充分利用CCD像元本身的探测能力 ,将合成图像的分辨率提高到原来的 1 4倍 ,而数据量仅为原来的 2倍 ,在遥感测量中具有非常实用的意义。将两幅实验拍摄的合成图像与单幅图像进行了比较 ,定性地验证了分析结果     

基于显微CT图像的岩芯孔隙分形特征

采用国内自主开发的高分辨率显微CT设备,对岩芯样本进行图像采集,运用数字图像分析方法获得图像中的岩芯孔隙目标,并以此为基础重建三维模型。然后基于分形理论,分别从二维图像和重建的三维模型角度计算孔隙的分形维数。最后,再采用基于多孔介质的分形模型对岩芯孔隙分形特征进行验证,得出岩芯的二维分形维数和三维分形维数之间的差值均值为1.000 3,最大偏差为0.004,很好地满足多孔介质分形模型中关于二维和三维分形维数的关系。     

Evaluation of the improved three‐dimensional resolution of a synchrotron radiation computed tomograph using a micro‐fabricated test pattern

A micro test pattern prepared by focused ion beam milling was used to evaluate the three‐dimensional resolution of a microtomograph at the BL20B2 beamline of SPring‐8. The resolutions along the direction within the tomographic slice plane and perpendicular to it were determined from the modulation transfer functions. The through‐plane resolution perpendicular to the tomographic slice was evaluated to be 8 µm, which corresponds to the spatial resolution of two‐dimensional radiographs. In contrast, the in‐plane resolution within the slice was evaluated to be 12 µm. Real‐space interpolation was performed prior to the tomographic reconstruction, giving an improved in‐plane resolution of 8.5 µm. However, the 8 µm pitch pattern was resolved in the interpolated slice image. To reflect this result, another resolution measure from the peak‐to‐valley difference plot was introduced. This resolution measure gave resolution limits of 7.4 µm for the in‐plane direction and 6.1 µm for the through‐plane direction. The three‐dimensional test pattern along with the interpolated reconstruction enables the quantitative evaluation of the spatial resolution of microtomographs.     

Design study of hard X-ray tomography system to obtain a spatial resolution of 100 nm

An optic-based X-ray tomography system of a high spatial resolution using a conventional X-ray tube was proposed. The system had several X-ray optics: multilayer mirror for monochromatic X-ray, capillary optic for focusing X-ray onto a sample, and objective zone plate. The X-ray tomography system was designed for obtaining a spatial resolution of 100 nm. Design parameters for each optic were determined and optimized by ray tracing in considering X-ray intensity and reflectivity. The X-ray tomography system with a spatial resolution of 100 nm will provide a good inspect tool in bio-medical field and semiconductor applications.     

Electro-optic measurement system with high spatial resolution utilizing poled polymer film as external probe tip

A new external electro-optic probing technology has been first demonstrated using a poling electro-optic (EO) polymer film, spin-coated on 20 nm thick grounding perspective aluminum layer which sputtered on a piece of ITO glass as a probe tip, the aluminum layer which has 30% reflectance ratio is also a reference coating. A interdigital electrode was measured, and the spatial resolution of less than was obtained. Voltage sensitivity was approximately . The probing beam reflected from the metal line is phase-modulated by the signal electric field in the EO polymer film, and then converted to amplitude modulation by interference with the reference beam reflected from the 30% reflective coating. The reference electrode makes sure that the most signal voltage drops down in the EO polymer film.     

Optimization of the in-line X-ray phase-contrast imaging setup considering edge-contrast enhancement and spatial resolution

Employing the approximation theory based on refraction and the definition of the total point-spread-function of the imaging system, the variation in the edge contrast of simple model samples is discussed with different source-to-sample and sample-to-detector distances, which actually means different spatial resolutions of the imaging system. The experiments were carried out with the Beamline 4W1A imaging setup at the Beijing Synchrotron Radiation Facility for simple model and insect samples. The results show that to obtain clear phase-contrast images of biologic tissues for the X-ray in-line imaging setup, with determined parameters such as the size of the X-ray source, the pixel size of the detector and the fixed source-to-sample distance, there is a range of optimized sample-to-detector distances. The analysis method discussed in this article can be helpful in optimizing the setup of X-ray in-line phase-contrast imaging.     

遥感影像信息量与空间分辨率的关系研究

目前,关于影像信息量的研究大多是注重信息量的计算模型,很少涉及空间分辨率与信息量之间的定量关系。为了对不同空间分辨率的遥感影像进行定量化评定,以信息论和模糊数学为理论基础,信息熵为测度,通过计算不同空间分辨率水平的全色影像和多光谱影像的信息量,对信息量与空间分辨率的关系进行直接量化模拟。结果表明,影像信息量随着空间分辨率的降低呈指数降低,空间分辨率在原影像基础上每增加一倍,影像信息量相应增加3~5倍。     

X光能点、放大倍率及针孔尺寸对空间分辨的影响

X光针孔成像是惯性约束聚变(ICF)研究中重要的诊断方法,对其点扩散函数的计算可用于图像重建和系统空间分辨的判断。对菲涅耳衍射公式进行了化简,分析了X光能点、针孔尺寸及放大倍率对针孔点扩散函数的影响。实验在保证成像能获得足够高信噪比的条件下,通过模拟获得在最佳空间分辨时所要的针孔大小、放大倍率和X光能点等参数。在流体力学不稳定性的静态样品定标实验中,通过模拟获得了针孔的调制传递函数(MTF),结合实验测量的结果反推获得分幅相机本身的MTF值。同时采用测刀边函数的方法获得了分幅相机本身的刀边函数,进而得到相机在各空间频率下的MTF值。两种方法得到的分幅相机MTF值一致,验证了通过菲涅耳衍射模拟X光针孔成像的可行性。     

Study of measuring methods on spatial resolution of a GEM imaging detector

In this paper, the limitations of the common method measuring intrinsic spatial resolution of the GEM imaging detector are presented. Through theoretical analysis and experimental verification, we have improved the common method to avoid these limitations. Using these improved methods, a more precise measurement of intrinsic spatial resolutions are obtained.