X射线光场成像技术研究

X射线三维成像技术是目前国内外X射线成像研究领域的一个研究热点.但针对一些特殊成像目标,传统X射线计算层析(CT)成像模式易出现投影信息缺失等问题,影响CT重建的图像质量,使得CT成像的应用受到一定的限制.本文主要研究了基于光场成像理论的X射线三维立体成像技术.首先从同步辐射光源模型出发,对X射线光场成像进行建模;然后,基于光场成像数字重聚焦理论,对成像目标场在深度方向上进行切片重建.结果表明:该方法可以实现对成像目标任一视角下任一深度的内部切片重建,但是由于光学聚焦过程中的离焦现象,会引入较为严重的背景噪声.当对其原始数据进行滤波后,再进行X射线光场重聚焦,可以有效消除重建伪影,提高图像的重建质量.本研究既有算法理论意义,又可应用于工业、医疗等较复杂目标的快速检测,具有较大的应用价值.     

复合组分材料的X射线定量相衬成像研究

对复合组分材料的应用和需求日益广泛,但如何精确地测量其定量结构信息仍是一个亟待解决的难题.建立了复合组分结构模型,利用X射线同轴相衬成像和相位恢复方法,分别进行了计算机模拟和实验研究,系统地分析了复合组分材料不同的密度差异对X射线相衬成像和相位恢复精度的影响以及噪声对定量相位恢复的影响.实验结果表明,利用X射线定量相衬...     

Toward one nanometer X-ray focusing: a complex refractive lens design

We report a design for one nanometer X-ray focusing by a complex refractive lens, which is capable of focusing 20 keV X-rays down to a lateral size of 0.92 nm （full-width at half-maximum （FWHM）） and an axial size of 98 nm （FWHM） with intensity gain of 49050. This complex refractive lens is comprised of a series of kinoform lenses, whose aperture is gradually matched to the converging trace of the X-ray beam so as to increase the numerical aperture （NA）. The theoretical principle of the proposed complex refractive lens is presented. The NAs of these lenses are calculated. The numerical simulation results demonstrate that the proposed design can focus the X-ray beam into sub-nanometer while remaining high gain.     

基于迭代重构算法改进晶体衍射分光X射线鬼成像的图像质量研究

X射线鬼成像是一种低剂量、非定域成像方法,对医疗诊断和生物成像具有重要意义.在基于晶体劳厄衍射分光的X射线鬼成像中,晶体振动会造成衍射光路上散斑的模糊,进而导致利用关联方法重构图像衬度和空间分辨的降低.本文系统分析了衍射光路上散斑图像的模糊程度对归一化二阶关联函数g(2)的最大值和半高全。宽的影响.模糊程度的增强会导致g(2)最大值的减小和半高全宽的展宽,在理论上证明了模糊程度会引起重构图像的衬度和分辨能力的降低.为解决上述问题,本文在衍射光路和直通光路的直接关联方法(CLH)的基础上提出C_LHE方法(CLH enhanced method).模拟实验表明C_LHE算法能同时改善图像衬度和提高重构分辨率,并且模糊程度增强时,G_LHE算法重构图像的峰值信噪比与先对直通光路的散斑图像进行高斯滤波处理再进行双光路关联计算方法(GLL)的差距扩大,同时保证其对噪声的鲁棒性.本文为晶体衍射分光的X射线鬼成像的实际应用提供可行的思路.     

Typical Microstructures of Chinese Medicines with X-Ray Microscopy in Phase Contrast

Due to the low absorption contrast of plant tissues, traditional x-ray radiography has not been included in the microscopic techniques used in the identification of traditional Chinese medicines （TCMs）. With the development of x-ray phase contrast imaging （XPCI） in recent years, weakly absorbing materials could also be imaged by x- rays. Here we investigate microstructures of TCMs utilizing XPCI based on a nano-focus x-ray tube. The results demonstrated that XPCI is capable of revealing the microstructures of TCMs used as judging criteria in the identification of TCMs. The major advantages of the new method are nondestructivity, no special demand for sample preparation and suitability for thick samples.     

Outline Imaging by THz Time Domain Spectroscopy

Outline imaging by THz time domain spectroscopy is proposed. Spectroscopic splitting at interface is reported, The principle of outline imaging is put forward. Experimental results demonstrate the feasibility of outline imaging by spectroscopic splitting, It is shown that clear out：line image of sample interface could be achieved easily by this technique. The spatial resolution is about 0.6mm. The THz-beam focus, the scanning step and the THz pulse width are the critical foctors affecting the imaging resolution. The signal-to-noise ratio of this technique could be improved greatly compared to the conventional transsion imaging.     

A Method for Quantitative Analysis of Chemical Mixtures with THz Time Domain Spectroscopy

A method for analysing chemical mixtures quantitatively with terahertz time domain spectroscopy is proposed. The experimental results demonstrate the feasibility of this technique. Transmission coefficient of THz wave at the sample surface is taken into account to improve the analytic precision, lsomer mixtures are chosen as the experimental samples. Compared to similar techniques, the analytic precision could be improved evidently in this method.     

利用定量相衬成像消除X射线同轴轮廓成像中散射的影响

在所有的相衬成像方法中，X射线同轴轮廓成像由于光路简单、不需要任何光学元件而备受关注.其缺点是无法直接消除散射的影响，从而限制了它在生物医学等领域中的应用.利用数字模拟方法研究了引入散射前后轮廓像的质量随样品到探测器距离的变化情况.模拟结果表明直接轮廓成像存在一个最佳成像距离，因而无法通过改变样品到探测器距离来减小散射的影响.利用定量相衬成像不受成像距离限制的特点，研究了远距离成像时散射的影响.结果表明，样品到探测器的距离增大到一个临界值时，散射对重构像的影响可降到一个极值，此时成像质量得到了明显改善. 关键词： 散射 X射线同轴轮廓成像 定量相衬成像     

利用数字重现电子全息图观测微电磁场分布

采用数字方法重构电子全息图，分别研究了荷电乳剂小球(0.31μm)的微电场分布及强磁材料中磁畴的磁力线分布精细结构.利用噪声消除及位相差放大技术提高了重现分辨率，并获得了一些新结果. 关键词：     

X射线全息记录过程中影响分辨率的主要因素分析

分析了Ｘ射线全息记录过程中影响分辨率的一些主要因素。在完全相干的条件下，Ｘ射线无透镜傅里叶变换全息图的最小分辨距离不可能小于记录时用的Ｘ射线聚束器的焦斑或滤波小孔的半径，而Ｘ射线同轴全息图不可能获得比记录介质的截止频率更高的分辨率。在部分相干的条件下，Ｘ射线无透镜傅里叶变换全息所要求的相干长度和分辨率与样品半径成二次线型关系。Ｙ射线同轴全息所要求的相干长度和分辨率的平方以及样品到全息图的距离成正比，而与样品尺寸无关。随着Ｘ射线全息图分辨率的提高，其所要求的相干长度将大幅度增长。 关键词：