Lensless imaging of magnetic nanostructures by X-ray spectro-holography

Our knowledge of the structure of matter is largely based on X-ray diffraction studies of periodic structures and the successful transformation (inversion) of the diffraction patterns into real-space atomic maps. But the determination of non-periodic nanoscale structures by X-rays is much more difficult. Inversion of the measured diffuse X-ray intensity patterns suffers from the intrinsic loss of phase information, and direct imaging methods are limited in resolution by the available X-ray optics. Here we demonstrate a versatile technique for imaging nanostructures, based on the use of resonantly tuned soft X-rays for scattering contrast and the direct Fourier inversion of a holographically formed interference pattern. Our implementation places the sample behind a lithographically manufactured mask with a micrometre-sized sample aperture and a nanometre-sized hole that defines a reference beam. As an example, we have used the resonant X-ray magnetic circular dichroism effect to image the random magnetic domain structure in a Co/Pt multilayer film with a spatial resolution of 50 nm. Our technique, which is a form of Fourier transform holography, is transferable to a wide variety of specimens, appears scalable to diffraction-limited resolution, and is well suited for ultrafast single-shot imaging with coherent X-ray free-electron laser sources.     

Nanoscale imaging magnetometry with diamond spins under ambient conditions

Magnetic resonance imaging and optical microscopy are key technologies in the life sciences. For microbiological studies, especially of the inner workings of single cells, optical microscopy is normally used because it easily achieves resolution close to the optical wavelength. But in conventional microscopy, diffraction limits the resolution to about half the wavelength. Recently, it was shown that this limit can be partly overcome by nonlinear imaging techniques, but there is still a barrier to reaching the molecular scale. In contrast, in magnetic resonance imaging the spatial resolution is not determined by diffraction; rather, it is limited by magnetic field sensitivity, and so can in principle go well below the optical wavelength. The sensitivity of magnetic resonance imaging has recently been improved enough to image single cells, and magnetic resonance force microscopy has succeeded in detecting single electrons and small nuclear spin ensembles. However, this technique currently requires cryogenic temperatures, which limit most potential biological applications. Alternatively, single-electron spin states can be detected optically, even at room temperature in some systems. Here we show how magneto-optical spin detection can be used to determine the location of a spin associated with a single nitrogen-vacancy centre in diamond with nanometre resolution under ambient conditions. By placing these nitrogen-vacancy spins in functionalized diamond nanocrystals, biologically specific magnetofluorescent spin markers can be produced. Significantly, we show that this nanometre-scale resolution can be achieved without any probes located closer than typical cell dimensions. Furthermore, we demonstrate the use of a single diamond spin as a scanning probe magnetometer to map nanoscale magnetic field variations. The potential impact of single-spin imaging at room temperature is far-reaching. It could lead to the capability to probe biologically relevant spins in living cells.     

基于全变差正则化的压缩感知毫米波成像方法

毫米波成像技术在人体安检领域有着重要的应用,它采用合成孔径雷达成像原理、宽带信号扫描方式实现三维高分辨率成像。针对其采集空域和频域数据冗余造成的信息和成本浪费问题,提出了在三维毫米波全息成像算法的基础上,采用一种傅里叶操作算子化的频率测量方法,从而实现压缩感知稀疏成像。同时依据成像场景,取图像差分域先验信息,引入了第三维频率维稀疏先验,利用三维全变差L1范数正则化方法将图像重构。实验通过真实回波数据成像效果的展示,证明了拥有高分辨率的三维毫米波图像恢复效果优异,并且与二维全变差正则化方法相比,三维全变差正则化方法重构的图像效果更佳,从而证明了所提方法的有效性。     

生物电阻抗复合检测及成像系统设计

根据临床应用中对疾病快速检测及定位的需求,提出了磁感应结合电阻抗的复合检测方式,利用磁感应方式无须直接接触,测量效率高.而采用加密和交叉测量的电阻抗测量方式,检测深度大,定位准确.实现了便携的一体化硬件设计,稳定的双恒流源激励,可加密的复合检测方式,交叉平面数据获取,三维图像重构成像等,通过复合电阻抗成像物理模型分析两种方式相结合后场域内电导率、分辨率、相对位置误差等,结合灵敏度关系分析该方式的特点,形成了包括精准前端采集、高效图像处理、适用范围广的软硬件系统,能够获得微弱的生理信号采集,满足床旁实时动态监测,快速医疗诊断,以及社区医疗初步筛查等需求.     

基于空间频率和小波变换的图像融合方法

为了更好的对多光谱图像和高分辨图像进行融合，根据小波变换有三个方向的高频细节这．特点，提出了一种计算空间频率的新方法。利用这种空间频率、IHS和小波变换方法对多光谱图像和高分辨图像进行了融合，得到了具有较好的空间分辨率和光谱信息的融合图像，并对融合图像进行了评价。实验结果表明该方法得到的融合图像优于传统IHS变换法和传统小波变换方法。     

IKONOS高分辨率遥感影像融合方法比较研究

由于应用需求的驱动,高分辨率遥感影像融合技术已成为卫星遥感信息处理领域的重要研究方向和热点课题.以贵阳地区2002年12月23日的IKONOS高分辨率遥感影像为实验数据,利用ENVI 4.3、PCI 9.0、ERDAS 9.1 3种遥感图像处理软件中的一些常用融合方法进行了融合实验,并对相应的融合结果进行了讨论和分析.结果表明,ERDAS 9.1中的PCA法融合效果最好.     

采用不同融合方法对土地利用现状进行自动分类的研究

LandsatTM图像在土地利用上的应用极为广泛,但TM图像的空间分辨率比较低,因此单独采用TM图像进行土地利用分类的精度也较低。通过融合高空间分辨率全色图像的高频纹理信息来提高TM图像的空间分辨率,使融合后的图像既保留TM图像的多光谱特性,又具有高空间分辨率的特性,易于图像的解译,达到提高自动分类的精度,减少自动分类的误差的目的。笔者运用IHS和KL融合方法,并对生成的新图像作分类精度比较研究,探讨融合图像在土地利用中的应用。     

基于正则化的SPACE-RIP并行磁共振成像重建算法

采用并行磁共振成像可以提高成像速度和图像分辨率,但这是以牺牲重建图像的信噪比为代价的。为此,该文提出了一种基于正则化的并行磁共振成像重建算法,降低由于阵列线圈的几何相关而造成的信噪比损失。以预扫描图像作为最后重建图像的先验信息,用L曲线方法求解最佳正则化参数。实验表明,该方法能较大限度地减弱噪声对重建结果的影响,当SPACE-RIP并行成像技术的加速因子达到4时,仍可得到高质量的高分辨率重建影像。重建后的图像质量良好,对临床诊断具有较高实用价值。     

基于正则化的SPACE-RIP并行磁共振成像重建算法

采用并行磁共振成像可以提高成像速度和图像分辨率,但这是以牺牲重建图像的信噪比为代价的。为此,该文提出了一种基于正则化的并行磁共振成像重建算法,降低由于阵列线圈的几何相关而造成的信噪比损失。以预扫描图像作为最后重建图像的先验信息,用L曲线方法求解最佳正则化参数。实验表明,该方法能较大限度地减弱噪声对重建结果的影响,当SPACE-RIP并行成像技术的加速因子达到4时,仍可得到高质量的高分辨率重建影像。重建后的图像质量良好,对临床诊断具有较高实用价值。     

一种基于非降采样Contourlet变换的遥感图像融合方法

给出了一种非降采样Contourlet变换和HIS变换相结合的遥感图像融合算法.非降采样Contourlet变换是一种平移不变的小波变换方法,且具有良好的方向选择性,其对图像做多分辨率分析得到的高频子带,有效地表达了图像中的细节特征信息.结合HIS变换,非降采样Contourlet变换将细节注入到多光谱图像得到的融合图像,不但具有较高的空间分辨率,而且有效保持了多光谱图像的光谱特征.实际的SPOT全色图像和TM多光谱波段融合结果表明,所提议方法的性能优于目前广泛使用的小波域方法如离散小波变换和A Trous小波变换以及Contourlet变换等融合方法.     

不同视角下海量高分辨率视频图像数据挖掘方法研究

当前高分辨率视频图像数据挖掘方法容易受到外界环境的干扰,提取的视频图像特征不可靠,且不同视角下提取的特征值有很大差异,导致视频图像数据挖掘精度大大降低。为此,提出一种新的不同视角下海量高分辨率视频图像数据挖掘方法,通过Harris角点检测方法对待挖掘高分辨率视频图像数据时空特征进行提取,依据高分辨率视频图像数据时空特征,通过自相关矩阵建立相同事物不同视角下的递归图,将递归图看作一幅图像,通过计算像素点的梯度向量构建递归特征描述符,对相同事物不同视角下的关联性进行挖掘,将具有相同递归图梯度特征的高分辨率视频图像数据汇聚在一起,实现数据挖掘。实验结果表明,所提方法挖掘精度高。     

Massively parallel manipulation of single cells and microparticles using optical images

The ability to manipulate biological cells and micrometre-scale particles plays an important role in many biological and colloidal science applications. However, conventional manipulation techniques--including optical tweezers, electrokinetic forces (electrophoresis, dielectrophoresis, travelling-wave dielectrophoresis), magnetic tweezers, acoustic traps and hydrodynamic flows--cannot achieve high resolution and high throughput at the same time. Optical tweezers offer high resolution for trapping single particles, but have a limited manipulation area owing to tight focusing requirements; on the other hand, electrokinetic forces and other mechanisms provide high throughput, but lack the flexibility or the spatial resolution necessary for controlling individual cells. Here we present an optical image-driven dielectrophoresis technique that permits high-resolution patterning of electric fields on a photoconductive surface for manipulating single particles. It requires 100,000 times less optical intensity than optical tweezers. Using an incoherent light source (a light-emitting diode or a halogen lamp) and a digital micromirror spatial light modulator, we have demonstrated parallel manipulation of 15,000 particle traps on a 1.3 x 1.0 mm2 area. With direct optical imaging control, multiple manipulation functions are combined to achieve complex, multi-step manipulation protocols.     

太赫兹成像和光谱在医疗领域的应用综述

在医疗领域中,人们对于太赫兹成像与光谱的研究早已不再停留于几年前的基础研究了,而是深入到了以组织、细胞、皮肤成像以及中医药学检测分析等的集中研究.相比传统意义上的医疗手段,如超声波、X光、核磁共振及红外线等,太赫兹波技术具有更加显著的优势,主要体现在宽带光谱分析能力强、分辨率高及耗能低等方面.围绕着太赫兹成像和光谱技术...     

基于双重字典及联合特征的遥感图像超分辨率算法

为了解决低分辨率遥感图像超分辨重建的问题,本文提出了一种基于双重字典及联合特征的遥感图像超分辨率算法.超分辨率重建技术目的就是根据低分辨率图像重建出原始高分辨率图像的高频信息.本文将图像的高频信息分解成为主高频信息和残差高频信息两个部分,然后针对主高频信息和残差高频信息,分别训练主高频字典和残差高频字典,并结合稀疏表示方法对图像进行重构.同时,为了建立更能反映图像内部结构信息的字典,本文联合图像的不同的结构特征,建立统一的字典.本文算法对图像取得较好的复原效果,复原出的高分辨率图像更接近于真实图像,与其他方法相比具有更好的主观和客观质量.     

Sparse Representation over Shared Coefficients in Multispectral Pansharpening

The pansharpening process is for obtaining an enhanced image with both high spatial and high spectral resolutions by fusing a panchromatic(PAN) image and a low spatial resolution multispectral(MS) image. Sparse Principal Component Analysis(SPCA) method has been proposed as a pansharpening method, which utilizes sparse coefficients and over-complete dictionaries to represent the remote sensing data. However, this method still has some drawbacks, such as the existence of the block effect. In this paper, based on SPCA, we propose the Sparse over Shared Coefficients(SSC), in which patches are extracted with a sliding distance of 1 pixel from a PAN image, and the MS image shares the sparse representation coefficients trained from the PAN image independently.The fused high-resolution MS image is reconstructed by K-SVD algorithm and iterations, and residual compensation is applied when the down-sampling constraint is not satisfied. The simulated experiment results demonstrate that the proposed SSC method outperforms SPCA and improves the overall effectiveness.     

A novel endorectal RF coil for high resolution MRI and spectroscopy of the prostate

The diagnosis of prostate diseases by magnetic resonance imaging (MRI) in vivo is sometimes difficult for the lower signal to noise ratio (SNR). To increase the SNR of the prostate image, we designed a RF coil that can be inserted into rectum and was named endorectal coil. The properties of RF coil were evaluated using a network analyzer. Moreover the images and spectroscopy of a special phantom were acquired and the results were compared to those of the commercial TORSO coil (G.E. Medical Systems, USA). Our coil gave a significantly higher SNR at the region of interest (ROI). The achieved high local SNR and resulting high spatial resolution would add more anatomic and biochemical information to the diagnosis of prostate diseases.     

A novel endorectal RF coil for high resolution MRI and spectroscopy of the prostate

MRI is a non invasive powerful imaging tool andhas been used in the diagnosis of various prostate dis eases. The excellent soft tissue contrast provided byMRI allows improved visualization of the prostateanatomy, surrounding critical structures (such as theneurovascular bundles and periurethral zone), and theextent of tumor spread. This improved contrast reso lution presents a distinct advantage over otherprostate imaging modalities such as transrectal ultra sound and comp…     

基于最小二乘法的卫星相机MTF测量

对于对地观察卫星而言,为了定量评定其成像质量,对其MTF进行测量是非常重要的,它为比较不同卫星的性能提供了理论依据。一般的在轨MTF测量主要是对已知目标进行成像,由于天气和图像混叠的影响,这种方法对星载程序带来了很大限制。本文提出使用最小二乘法测量星载相机的MTF．对同一景物两次成像．一次采用高分辨率模式．另一次使用低分辨率模式,当两者分辨率比值足够高时,就可以通过将高分辨率图像与一个点扩散函数卷积和乏采样模拟得到低分辨率图像．并通过迭代使模拟图像与实测低分辨率图像的差在最小二乘意义下达到最小,以此得到点扩散函数。一旦迭代过程收敛,通过对点扩散函数进行傅立叶变换即可得到待测低分辨率图像的MTF。     

一种具有安全特性的压缩全息成像方法

本文提出一种具有安全特性的压缩全息成像技术来解决当下存在于全息成像方面的安全问题.该方法可以在全息成像场景过程中实现光学加密、光学隐藏和光学压缩功能,能够在保护图像信息安全的同时,实现对数据的压缩.该方法将主对象引入经典Mach-Zehnder干涉仪的参考路径中,实现参考波的空间调制,形成参考光场的二维空间分布.之后,对象信息被加密并隐藏到菲涅耳域中目标光束和参考光束的相干成像过程中的主目标信息中,实现对图像的安全保护;同时,安全物体全息图被进一步压缩采样,单像素检测器只需记录较少数据,就可表示原始成像对象.该技术大大减少了对象的数据采集量,可以在纯光系统下安全地获得压缩对象,这是全息成像方法的一大突破,也有望突破全息影像在3DTV、医学诊断、实时全息TV等领域中,影像数据量受限的瓶颈.凭借全光学手段实现光学安全的可行性,本文提出的方法对实现全光网络、近地和星际激光通信链路等方面也有重要参考意义.     

光声成像技术及其医学应用进展

光声成像技术是一种具有广泛应用前景的无损生物医学成像技术,其结合了纯光学成像高选择特性和纯超声成像中深穿透特性的优点,克服了光在组织中的高散射限制,实现了对活体深层组织的高分辨、高对比度成像．近年,光声成像技术得到了飞速发展,从技术层面到应用层面都在不断突破．文中将阐述光声成像技术的基本原理,介绍各种光声成像方法模式的发展现状,总结光声成像技术的优点并展望其在生物医学领域的应用前景及面临的挑战．