菲涅耳波带板无运动卷积全息术

提出了菲涅耳波带板(FZP)无运动卷积全息术.该技术使用均匀扩展光源，使得从光源不同位置发出的光在经过FZP编码孔径之后，在物体上形成多个菲涅耳波带板投影叠加.物体的全息图是FZP投影光强分布函数与物体的光强分布函数的卷积，无需机械运动便得到物体的扫描全息图.采用数字相关解码方法实现全息图的再现.用蒙特卡罗方法模拟了菲涅耳波带板入射光束在经过散射介质以后，其出射光强分布随散射介质厚度的变化规律.结果表明:当散射介质厚度为5 cm时，出射光束依然基本保持菲涅耳波带板形式的光强分布.对嵌埋在浓度为1%的Intralipid散射溶液中直径为0.4mm的金属丝进行成像实验，分别得到当散射介质厚度为1cm、3cm和5cm时的再现像，实验验证了菲涅耳波带板无运动卷积全息术用于高散射介质中物体成像的可行性.     

菲涅耳波带板无运动卷积偏振选通成像研究

提出了菲涅耳波带板(FZP)无运动卷积偏振选通全息术,该技术的原理与菲涅耳波带板扫描全息术相同,但在成像系统结构上作了重大改进,改进内容主要有两个方面:第一,使用扩展光源,用多个菲涅耳波带板在物体上的投影叠加形成卷积运算来取代机械扫描,克服了扫描造成的系统不稳定性和限制实际应用的耗时问题;第二,用CCD取代光电倍增管,使物体上所有的点都同时成像在CCD靶面上,达到实时采集整个全息图的目的。对线偏振光和圆偏振光经过散射介质脂肪乳剂(Intralipid)溶液后偏振度的变化规律进行了实验研究,研究表明,在米氏散射区,圆偏振光比线偏振光更容易保持偏振态。应用菲涅耳波带板无运动卷积偏振选通成像系统,采用圆偏振光作为入射光,对嵌埋在浓度为1%、深度为2 cm的脂肪乳剂溶液中的金属丝(直径0.4 mm)进行了成像实验,结果表明,菲涅耳波带板无运动卷积偏振选通全息术原理是可行的。     

基于菲涅耳波带板扫描全息术的光学层析成像

基于光学扫描全息术原理和编码孔径层析成像技术,提出了一种三维物体层析成像技术——菲涅耳波带板扫描全息术。该技术通过将物体的光强分布函数与菲涅耳波带板的光强分布函数进行卷积运算来得到物体的扫描全息图,通过相关解卷积的方法来进行扫描全息图的数字重建。依据该技术原理设计了实验系统,系统结构简单紧凑,具有三维物体层析成像功能。提出用数字高通滤波器来减少重建图像的背景噪声。计算机仿真及对实物的扫描记录和重建实验结果表明,该技术原理正确,用于三维物体层析成像是可行的,用数字高通滤波的方法提高重建图像的对比度是有效的。     

应用反射型球面菲涅耳波带片的成像物镜设计

设计了一种应用球面菲涅耳波带反射面与非球面反射面结合的成像物镜。对球面结构的菲涅耳波带反射面进行分析,推导了球面菲涅耳波带反射面近似替代非球面的方法,采用单片球面菲涅耳波带反射面和三片非球面反射面设计成像物镜,在放大倍数100×、视场角120°、菲涅耳数2.5情况下,调制传递函数在放大成像侧可实现0.6 lp/mm的40%以上,畸变小于2.2%。该设计方法为菲涅耳波带片应用于可见光成像提供了参考,并随着菲涅耳器件加工技术的不断发展具有良好的应用前景。     

复合扫描全息术及透过强散射介质三维成像研究

应用菲涅耳波带片光学扫描全息术原理，研究强散射介质中吸收体的三维成像.针对由成像物体强散射背景产生的背景噪音，提出复合扫描全息术成像方法.实验中应用这一方法，对嵌埋在浓度为1%，深度为1.7 cm的脂肪乳剂中的吸收体成像，得到了信噪比和对比度较好的再现像.在此基础上，对复合扫描全息成像系统的信噪比，对比度及分辨率等性能进行了深入的理论分析和实验测试.研究表明，与单一模式相比，复合扫描全息术在信噪比和对比度方面有较大改善，但分辨率还需进一步提高.     

计算全息显示技术的研究

基于电寻址液晶光阀实验系统,利用计算像面全息法制作全息图并实现像的再现.综合比较物点散射法、层析法和主菲涅耳波带法3种计算全息方法的优劣,选择物点散射法以四级迂回相位编码的方式,得到三维物体的计算全息图.通过烟雾散射的丁达尔效应观察圆柱体的全息像,采用空心立方体优化成像的清晰度和对比度.     

相位型波带板应用于大尺度X射线源成像的分析与模拟

针对大尺度物体的keV-X射线高分辨成像,分析了相位型菲涅耳波带板(FPZP)对物平面1mm区域内点源的成像,确定像的空间分布具有不变性,提出了一种FPZP对扩展光源成像的计算方法.使用这一方法,模拟了放大倍数为10的典型实验条件下最外环宽0.35 μm的FPZ对扩展单色光源的成像.结果表明,随着扩展光源尺度的增加,像的对比度降低.FPZP的负1级和0级衍射是导致像的背景增强和对比度降低的主要因素,并相应导致成像对物方的空间分辨能力下降.对于强度空间分布为正弦调制、对比度为1的1mm尺度方形光源,像的对比度低于0.4,物方分辨能力为0.75 μm.     

菲涅耳波带板X射线成像的快速计算方法

菲涅耳波带板直接成像,应用到激光等离子体或惯性约束聚变靶的X射线成像诊断,可实现μm甚至亚μm的空间分辨能力。在对成像进行数值模拟时,考虑到光源的光谱带宽和几何尺度对成像的影响,要进行菲涅耳-基尔霍夫衍射积分与卷积等数值计算,需占用大量计算机内存并且耗费运行机时。改进了数值计算方法,采用了蒙特卡罗积分法和新的卷积算法。模拟了菲涅耳波带板对大尺度多色X射线源的二维成像,新算法与以往算法相比,可显著减少运算机时,在台式机上实现模拟成像的快速计算。结果表明随着光源尺度增大、光谱带宽增加,像的背景增强,导致反衬度与成像质量下降。     

KB镜成像模拟以及与菲涅耳波带板成像的比较

采用坐标变换方法自编光线追迹程序模拟了Kirkpatrick-Baez镜在X射线波段的掠入射成像,获得了视场、分辨率等结果.比较了给定参量条件下Kirkpatrick-Baez镜与菲涅耳波带板两种高分辨X射线成像的特性,给出两者各自适用范围.Kirkpatrick-Baez镜成像有比较高的系统效率,在视场中心的空间分辨能力可达0.71μm,但偏离视场中心±200μm,空间分辨能力显著下降至6μm,适用于较小视场的成像.菲涅耳波带板成像不仅在视场中心可以实现0.39μm的空间分辨能力,偏离视场中心达±13 mm,空间分辨能力也几乎不变,可实现大视场高分辨成像.     

KB镜成像模拟以及与菲涅耳波带板成像的比较

采用坐标变换方法自编光线追迹程序模拟了Kirkpatrick-Baez镜在X射线波段的掠入射成像,获得了视场、分辨率等结果.比较了给定参量条件下Kirkpatrick-Baez镜与菲涅耳波带板两种高分辨X射线成像的特性,给出两者各自适用范围.Kirkpatrick-Baez镜成像有比较高的系统效率,在视场中心的空间分辨能力可达0.71 μm,但偏离视场中心±200 μm,空间分辨能力显著下降至6 μm,适用于较小视场的成像.菲涅耳波带板成像不仅在视场中心可以实现0.39 μm的空间分辨能力,偏离视场中心达±13 mm,空间分辨能力也几乎不变,可实现大视场高分辨成像.     

Quantitative assessment of effects of phase aberration and noise on high-frame-rate imaging

The goal of this paper is to quantitatively study effects of phase aberration and noise on high-frame-rate (HFR) imaging using a set of traditional and new parameters. These parameters include the traditional −6-dB lateral resolution, and new parameters called the energy ratio (ER) and the sidelobe ratio (SR). ER is the ratio between the total energy of sidelobe and the total energy of mainlobe of a point spread function (PSF) of an imaging system. SR is the ratio between the peak value of the sidelobe and the peak value of the mainlobe of the PSF. In the paper, both simulation and experiment are conducted for a quantitative assessment and comparison of the effects of phase aberration and noise on the HFR and the conventional delay-and-sum (D&S) imaging methods with the set of parameters. In the HFR imaging method, steered plane waves (SPWs) and limited-diffraction beams (LDBs) are used in transmission, and received signals are processed with the Fast Fourier Transform to reconstruct images. In the D&S imaging method, beams focused at a fixed depth are used in transmission and dynamically focused beams are used in reception for image reconstruction.The simulation results show that the average differences between the −6-dB lateral beam widths of the HFR imaging and the D&S imaging methods are −0.1337 mm for SPW and −0.1481 mm for LDB, which means that the HFR imaging method has a higher lateral image resolution than the D&S imaging method since the values are negative. In experiments, the average differences are also negative, i.e., −0.2804 mm for SPW and −0.3365 mm for LDB. The results for the changes of ER and SR between the HFR and the D&S imaging methods have negative values, too. After introducing phase aberration and noise, both simulations and experiments show that the HFR imaging method has also less change in the −6-dB lateral resolution, ER, and SR as compared to the conventional D&S imaging method. This means that the HFR imaging method is less sensitive to the phase aberration and noise.Based on the study of the new parameters on the HFR and the D&S imaging methods, it is expected that the new parameters can also be applied to assess quality of other imaging methods.     

红外目标湍流退化图像的优化复原算法

提出了基于最速下降法的湍流退化图像盲目复原算法。将图像转换到频域中，建立一个基于目标图像和点扩展函数频谱的目标函数，通过迭代方式采用最速下降优化方法来极小化该目标函数，并利用傅里叶变换和反变换将目标图像和点扩展函数在频域和空域之间进行变换，在每次迭代中交替加入约束条件进行反复修正，以便取得预期的图像恢复效果，增强算法的稳定性和抗噪能力。针对红外目标湍流退化图像，在微机上对算法进行了一系列复原验证实验。实验结果表明：该文算法复原效果稳定，抗噪能力强，具有实用价值。     

中子半影成像的散射中子对点扩展函数的影响

基于ICF中子半影成像分辨力的要求,利用蒙特卡罗方法,模拟了4种系统模型的点扩展函数,分析半影孔装置、靶室和中子束流通道的钢管、高密度内爆靶丸的散射中子对点扩展函数的影响;模拟了平面中子源在4种模型中的半影成像,并用维纳滤波方法重建,分析了散射中子对中子半影成像诊断的影响。模拟结果表明:半影孔装置、靶室等的散射中子不会造成点扩展函数的变形,仅仅增加本底,对诊断的影响可以忽略;高密度内爆靶丸的散射中子会造成点扩展函数的平滑,但对诊断的影响有限。     

A robust algorithm for high-resolution dynamic MRI based on the partially separable functions model

A recently developed partially separable functions (PSF) model can be used to generate high-resolution dynamic magnetic resonance imaging (MRI). However, this method could not robustly reconstruct high-quality MR images because the estimation of the PSF parameters is often interfered by the noise of the sampled MR data. To improve the robustness of MRI reconstruction using the PSF model, we proposed a new algorithm to estimate the PSF parameters by jointly using robust principal component analysis and modified truncated singular value decomposition regularization methods, instead of using the least square fitting method in the original PSF model. The experiment results of in vivo cardiac MRI demonstrated that the proposed algorithm can robustly reconstruct dynamic MR images with higher signal-to-noise ratio and clearer anatomical structures in comparison with the previous PSF model.     

Effects of mask-alignment error on point spread function for multi-level Fresnel diffractive lenses

The full aperture complex amplitude transmittance function of a multi-level diffraction lens with maskalignment errors was derived based on scalar diffraction theory. The point spread function(PSF) was calculated by the Kirchhoff diffraction integral. It is found that the radius of the Airy disk increases with the increase of the error in the direction of misalignment, and the image center shifts along the direction of misalignment. A fourlevel diffractive lens with a diameter of 80 mm was fabricated, and its PSF and diffraction efficiency of +1 st order were calculated and measured. The distribution of PSF is consistent with the calculated results, and the tested diffraction efficiency is slightly smaller than the calculated value; the relative error is 5.71%.     

基于目标和点扩展函数联合估计的点源目标图像近视解卷积

在传统的基于波前探测的解卷积方法中,由波前探测得到的点扩展函数被认为是精确的,并用维纳滤波进行复原,但是点扩展函数不可避免地存在误差,所以最终的复原目标图像质量不佳.为了解决该难题,提出了基于目标和点扩展函数联合估计的图像近视解卷积算法.它运用了点扩展函数和目标的先验信息,对点扩展函数和目标进行了规整和进一步约束,从而得到更优的恢复图像质量.对该方法的原理和实现过程进行了阐述,并将其运用于室内点源目标数据中.实验结果证明,与维纳滤波方法相比,该方法使图像恢复的效果得到明显改善.     

气动光学效应降晰函数辨识的最小二乘法研究

在对由气动光学效应引起的图像模糊进行理论分析的基础上,提出了用最小二乘法(LS)对气动光学效应降晰函数进行辨识的方法。利用所建的模型对试验图像进行图像复原,提高了复原图像的信噪比,减小了复原以后的图像误差。     

PET image reconstruction with a system matrix containing point spread function derived from single photon incidence response

A point spread function(PSF)for the blurring component in positron emission tomography(PET)is studied.The PSF matrix is derived from the single photon incidence response function.A statistical iterative reconstruction(IR)method based on the system matrix containing the PSF is developed.More specifically,the gamma photon incidence upon a crystal array is simulated by Monte Carlo(MC)simulation,and then the single photon incidence response functions are calculated.Subsequently,the single photon incidence response functions are used to compute the coincidence blurring factor according to the physical process of PET coincidence detection.Through weighting the ordinary system matrix response by the coincidence blurring factors,the IR system matrix containing the PSF is finally established.By using this system matrix,the image is reconstructed by an ordered subset expectation maximization(OSEM)algorithm.The experimental results show that the proposed system matrix can substantially improve the image radial resolution,contrast,and noise property.Furthermore,the simulated single gamma-ray incidence response function depends only on the crystal configuration,so the method could be extended to any PET scanner with the same detector crystal configuration.     

Spatial resolution in echo planar imaging: shifting the acquisition window in k-space

Single-shot echo planar imaging (EPI) is one of the most suitable techniques for very fast image acquisition, especially in functional MRI. In standard EPI schemes the k-space center is sampled in the middle of the acquisition train. This leads to longer echo times for higher spatial resolutions, as well as reduced signal intensity and signal-to-noise ratio. Therefore, echo shifting to lower echo times is often used. After a brief overview on the theoretical background of various point-spread-functions (PSF) computational simulations are presented, which quantify the modulation amplitude of a binary test object sampled with either standard, zero-filled or shifted k-space acquisition. The results suggest that echo-shifting with zero-filling is not advantageous, not even with small matrix sizes, and that echo-shifting with additional acquisition of outer k-space lines decreases the modulation amplitude only slightly. Simulations were also performed on noise-corrupted test objects, indicating that the use of the echo-shifted scheme causes resolution loss of up to 30% compared to the standard scheme for a 128 by 128 pixel matrix at a noise level of 20%. Finally, in vivo experiments using different echo shifts are presented and the characteristics of signal and noise with varying TE are quantified.     

基于图像复原的高光谱图像前向像移补偿

为了提高高光谱图像空间维的图像分辨力,针对航空遥感器成像时由前向像移造成的图像模糊提出了像移补偿方法。分析了航空遥感器前向像移造成图像模糊的退化机制,对运动模糊图像进行了预处理;估计了点扩散函数和噪声功率,使用改进的维纳滤波算法对图像进行复原并以绝对平均误差、峰值信噪比作为评价标准进行了实验。在估计出模糊图像点扩散函数和噪声功率的情况下得到的结果显示:与传统的维纳滤波复原算法相比,改进的维纳滤波复原算法的图像绝对平均误差降低了9.31%,峰值信噪比提高了13.98%,表明提出的算法能够有效改善高光谱图像的像质。