金属圆柱腔体中使用非均一背景增强微波断层成像

针对基于圆柱金属腔体的微波断层成像系统,提出了一种利用非均一背景增强系统获取目标信息能力的方法.该方法通过在腔体内放置已知物体构成非均一背景,这样不但能利用背景的先验信息,而且可以增加等效辐射源对目标进行探测.首先,利用矩量法计算圆柱金属腔体内非均一背景的格林函数和离散积分算子,并对离散积分算子进行奇异值谱和条件数分析,在理论上证明该方法的可行性;然后,利用基于有限元的对比源逆成像法对均一背景、有耗非均一背景和无耗非均一背景三种情况进行仿真研究;最后对仿真结果进行了误差分析和比较.仿真结果表明,该方法可以提高反演收敛速度和结果准确度,有耗非均一背景略优于无耗非均一背景.该方法可以在不改变硬件系统和算法的情况下得到更准确的反演结果,可应用于医学成像与工业无损探测.     

基于交替隐式有限差分法的快速早期乳腺癌时域微波断层成像

采用时域微波断层成像技术进行早期乳腺癌检测能够准确地获得乳房的电参数分布,具有明确的物理解释和医学诊断价值.临床应用讲究即时性,为了提高检测的速度,本文将交替隐式有限差分法应用到乳腺癌检测中,基于正反演时间步进成像算法进行成像分析,结果显示在保证精度的前提下,采用交替隐式有限差分法的成像时间可缩短为传统时域有限差分法的23%,提高了微波断层成像技术的临床可应用性.     

基于随机场照射的最优微波成像

近年来,电磁计算成像的理论和技术得到了广泛的研究和发展,其中基于随机场照射的微波成像引起了诸多关注.与传统成像方法的连续波照射不同,基于随机场照射的成像方法以随机照射的方式获取多组非相关的目标散射测量值,经过反演计算就能提取散射目标体的轮廓和形状等信息.基于阵列天线理论,本文理论分析并实验验证了一种最优的二维微波成像系统,能够使用最少的天线单元实现随机照射,通过最少的测量次数完成矩阵求逆并得到重建图像.该系统主要有以下两个创新点:完全随机照射的获取和成像系统最优参数的选取.与基于超材料的成像系统相比,本文通过对1 bit相位调制器随机相位调制的方式获取随机场照射,使得每个天线单元都处于工作状态,因此整个系统的能量效率更高.此外,所述单频成像系统还具有频谱效率高、结构简单、成本低等优点,在安检、室内定位等不同场景中具有潜在的应用价值.     

一种优化区域知识先验的稀疏角锥束X射线发光断层成像方法

锥束X射线发光断层（CB-XLCT）成像是一种可在生物体外对早期肿瘤进行有效检测的新型医学成像技术。稀疏角CB-XLCT成像加速了CB-XLCT技术的实时成像转化进程。然而,相对于传统多角度成像,稀疏角CB-XLCT成像的逆问题病态性明显加剧,这对传统成像方法的有效扩展提出了挑战。基于稀疏非凸L_p（01范数和L₀范数的代表算法验证所提方法的有效性和稳健性。实验结果表明,所提方法不仅可有效求解稀疏角CB-XLCT成像逆问题,还具有良好的可扩展性。     

一种基于非锐化掩蔽模型的无偏振片成像技术

液晶透镜是一种新兴的可以电控调焦的液晶器件,无需机械移动就可以实现对焦、变焦和深度测量,因此被广泛应用于摄影摄像、显微成像、虚拟现实等领域。提出一种优化的液晶透镜无偏振片成像技术。该技术结合非锐化掩蔽模型,通过分析图像像素值的变化,估算得到环境光中寻常光分量的占比,并使用非对焦图像和对焦图像进行处理,获得高质量图像。实验结果表明,优化后的技术能够有效增强图像对比度,获得优质图像。     

一种用于非制冷红外热成像系统的图像增强方法

在基于微悬臂梁的光学读出红外成像系统中,获得的红外图像有明显噪声,甚至有连续噪点组成孔洞,让目标难以辨识出来,因此提出基于特征模板卷积的红外图像增强方法。利用Hough变换根据微悬臂梁结构的特点,获得特征卷积模板的尺寸信息,根据成像系统特点建立卷积模板。让模板在图像内逐点卷积,建立评价参数阈值消除图像内噪声。进行均值滤波来填补噪声点及FPA单元的间隔,获得增强后的红外图像。实验结果表明,方法不仅能够有效增强光学读出红外成像系统的成像质量,对于普通存在噪声的图像也有良好的噪声消除效果。     

一种用于中子散射成像的快速反投影重建方法

针对中子散射成像建立了一种快速反投影重建方法,这种方法首先根据每一个散射事件确定粒子可能所在的空间范围,然后该空间范围中进行重建,大大减少了重建的运行时间。应用所建立的方法对模拟的成像数据进行处理,结果表明:重建源与实际源的位向一致,对1000个散射数据进行处理,用时约3 s;对5探测单元成像得到的模拟数据处理,得到重建后点源的位向分辨为8.0°;重建源的位向分辨不随设定重建平面的位置而改变,但重建平面距探测平面越近,重建速度越快;当重建平面达到一定尺寸时,继续增加大重建平面尺寸,重建的运行时间增加不明显,该方法在大视场空间探测成像应用中,具有较高的重建效率。     

一种用于中子散射成像的快速反投影重建方法

针对中子散射成像建立了一种快速反投影重建方法,这种方法首先根据每一个散射事件确定粒子可能所在的空间范围,然后该空间范围中进行重建,大大减少了重建的运行时间。应用所建立的方法对模拟的成像数据进行处理,结果表明：重建源与实际源的位向一致,对1000个散射数据进行处理,用时约3 s;对5探测单元成像得到的模拟数据处理,得到重建后点源的位向分辨为8.0;重建源的位向分辨不随设定重建平面的位置而改变,但重建平面距探测平面越近,重建速度越快;当重建平面达到一定尺寸时,继续增加大重建平面尺寸,重建的运行时间增加不明显,该方法在大视场空间探测成像应用中,具有较高的重建效率。     

一种乳腺癌检测的改进微波共焦成像方法

尝试引入因媒质不均匀而产生的折射效应,改进原有算法.共焦过程选用鲁棒的Capon波束成形（RCB）算法.乳房模型选用较为简单的三维（3-D）半球,为了更好地描述人体组织电参数的色散特性,各组织建模为多极柯尔-柯尔（Cole-Cole）媒质.在超宽带（UWB）平面波激励下,利用时域有限差分（FDTD）法模拟电波传播.数值应用中,乳房植入两个半径3 mm球状肿瘤,分别应用原有微波共焦成像方法和改进方法检测乳腺肿瘤.仿真结果对比显示：改进方法在复杂度略微增加的同时,提高了计算精度.     

Systematic distortion in cosmic microwave background maps

To minimize instrumentally the induced systematic errors, cosmic microwave background (CMB) anisotropy experiments measure temperature differences across the sky using pairs of horn antennas, temperature map is recovered from temperature difference obtained in sky survey through a map-making procedure. To inspect and calibrate residual systematic errors in the recovered temperature maps is important as most previous studies of cosmology are based on these maps. By analyzing pixel-ring coupling and latitude dependence of CMB temperatures, we find notable systematic deviation from CMB Gaussianity in released Wilkinson Microwave Anisotropy Probe (WMAP) maps. The detected deviation cannot be explained by the best-fit LCDM cosmological model at a confidence level above 99% and cannot be ignored for a precision cosmology study. Supported by the National Natural Science Foundation of China (Grant No. 10533020), the National Basic Research Program of China (Grant No. 2009CB-824800), and the Directional Research Project of the Chinese Academy of Sciences (Grant No. KJCX2-YW-T03) Contributed by LI TiPei     

Recent advances in bioluminescence tomography: methodology and system as well as application

Optical molecular imaging has been rapidly developed to noninvasively visualize in vivo physiological and pathological processes involved in normal and suffering organisms at the cellular and molecular levels, in which advanced optical imaging technology and modern molecular biology are being combined to provide a state‐of‐the‐art tool for preclinical biomedical research. Among optical molecular imaging modalities, bioluminescence tomography (BLT) has experienced considerable growth and attracted much attention in recent years for its excellent performance, unique advantages, and high cost‐effectiveness. This article focuses on the genesis and development of BLT, especially for its computational methodology, imaging system, and biomedical application. An overview of the advantages and challenges of the conventional planar bioluminescence imaging technique is first described in comparison with currently available molecular imaging modalities. The imaging algorithms for inverse source reconstruction are classified and summarized according to different a priori knowledge, followed by a simple depiction of the uniqueness theorems of BLT solution. Diverse imaging systems for obtaining three‐dimensional quantitative information of internal bioluminescent sources are then reviewed. The latest application examples of BLT in tumor study and drug discovery are introduced and compared with other mature imaging technologies. Finally, the paper is concluded and an attractive prospect for BLT is predicted.     

An optical fiber sensor based on cladding photoluminescence for high power microwave plasma ultraviolet lamps used in water treatment

Low-pressure mercury lamps are commonly used for germicidal applications such as water and wastewater sterilisation. The germicidal effect is due to the emission of light at 254 nm, which leads to the destruction of most waterborne bacteria. The Microwave plasma ultraviolet lamp (MPUVL) is a new technology for generating a high intensity ultraviolet (UV) light. A Fluorescent optical fiber based sensor is presented which is used for monitoring the output of a high power microwave UV light source and its control. This sensor is a fiber which has had its cladding removed and been coated with a phosphor doped polymer. This paper was originally presented at the 2001 International Conference (2nd Joint OSJ-SPIE Conference) on Optical Engineering for Sensing and Nanotechnology, ICOSN 2001 which was held June 6–8, 2001 at the Pacifico-Yokohama Conference Center, Yokohama, Japan.