血液灌注率动态变化的光学监测

研究了利用激光散斑测速原理结合CCD成像技术对大鼠肠系膜上血液灌注变化进行监测的技术。设计了用于监测大鼠肠系膜上微血管血流速度的激光散斑测量系统,通过模型实验对该测量系统的技术参数、测试精度进行分析,在此基础上,对热作用下大鼠肠系膜上微血管血流速度的变化进行动态监测,结合CCD成像技术,监测血管直径的变化,从而获得不同温度下血液灌注率的变化。     

Laser Doppler perfusion imaging by dynamic light scattering

A laser Doppler perfusion imaging technique based on dynamic light scattering in tissue is reported. When a laser beam sequentially scans the tissue (maximal area approximately 12 cm×12 cm), moving blood cells generate Doppler components in the backscattered light. A fraction of this light is detected by a remote photodiode and converted into an electrical signal. In the signal processor, a signal proportional to the tissue perfusion at each measurement point is calculated and stored. When the scanning procedure is completed, the system generates a color-coded perfusion image on a monitor. A perfusion image is typically built up of data from 4096 measurement sites, recorded during a time period of 4 min. This image has a spatial resolution of about 2 mm. A theory for the system inherent amplification factor dependence on the distance between individual measurement points and detector is proposed and correction measures are presented. Performance results for the laser Doppler perfusion imager obtained with a flow simulator are presented. The advantages of the method are discussed     

New insights into image processing of cortical blood flow monitors using laser speckle imaging

Laser speckle imaging has increasingly become a viable technique for real-time medical imaging. However, the computational intricacies and the viewing experience involved limit its usefulness for real-time monitors such as those intended for neurosurgical applications. In this paper, we propose a new technique, tLASCA, which processes statistics primarily in the temporal direction using the laser speckle contrast analysis (LASCA) equation, proposed by Briers and Webster. This technique is thoroughly compared with the existing techniques for signal processing of laser speckle images, including, the spatial-based sLASCA and the temporal-based modified laser speckle imaging (mLSI) techniques. sLASCA is an improvement of the basic LASCA technique. In sLASCA, the derived contrasts are further averaged over a predetermined number of raw speckle images. mLSI, on the other hand, is the technique in which temporal statistics are processed using the equation described by Ohtsubo and Asakura. tLASCA preserves the original image resolution similar to mLSI. tLASCA outperforms sLASCA (window size M = 5) with faster convergence of K values (5.32 versus 20.56 s), shorter per-frame processing time (0.34 versus 2.51 s), and better subjective and objective quality evaluations of contrast images. tLASCA also outperforms mLSI with faster convergence of K values (5.32 s) compared to N values (10.44 s), shorter per-frame processing time (0.34 versus 0.91 s), smaller intensity fluctuations among frames (8%-10% versus 15%-35%), and better subjective and objective quality evaluations of contrast images. As laser speckle imaging becomes an important tool for real-time monitoring of blood flows and vascular perfusion, tLASCA is proven to be the technique of choice.     

Efficient Processing of Laser Speckle Contrast Images

Though laser speckle contrast imaging enables the measurement of scattering particle dynamics with high temporal resolution, the subsequent processing has previously been much slower. In prior studies, generating a laser speckle contrast image required about 1 s to process a raw image potentially collected in 10 ms or less. In this paper, novel algorithms are described which are demonstrated to convert 291 raw images per second to laser speckle contrast images and as many as 410 laser speckle contrast images per second to relative correlation time images. As long as image processing occurs during image acquisition, these algorithms render processing time irrelevant in most circumstances and enable real-time imaging of blood flow dynamics.      

Confocal laser speckle autocorrelation imaging of dynamic flow in microvasculature

Laser speckle imaging has been widely used for in-vivo visualization of blood perfusion in biological tissues.However,existing laser speckle imaging techniques suffer from limited quantification accuracy and spatial resolution.Here we re-port a novel design and implementation of a powerful laser speckle imaging platform to solve the two critical limitations.The core technique of our platform is a combination of line scan confocal microscopy with laser speckle autocorrelation imaging,which is termed Line Scan Laser Speckle Autocorrelation Imaging(LS-LSAI).The technical advantages of LS-LSAI include high spatial resolution(~4.4μm)for visualizing and quantifying blood flow in microvessels,as well as video-rate imaging speed for tracing dynamic flow.     

Anisotropic processing of laser speckle images improves spatiotemporal resolution

Laser speckle contrast imaging (LSCI) is a full field optical imaging technique, capable of imaging blood flow without the introduction of any exogenous dyes. Spatial and temporal resolution in LSCI images depend on how pixels are chosen from the raw image stack for contrast processing. However, all processing schemes are based on isotropic treatment of the spatial neighborhood about each pixel, restricting further improvement in spatiotemporal resolution and image quality. We present a novel spatiotemporal processing scheme for LSCI where the spatial neighborhood is anisotropic, that is, restricted along a specific direction that matches direction of blood flow. The technique allows for a significant increase in temporal resolution, from conventionally used 40 or 80 frames to just three frames; while simultaneously achieving 23% and 47% higher signal-to-noise ratios over concurrent spatiotemporal schemes, when imaging rapid and slow functional changes in blood flow, respectively. We present the concept, justification, and performance evaluation of the novel scheme and demonstrate its suitability for imaging rapid changes in blood flow. Anisotropic LSCI was able to monitor the heart rate associated fluctuations in intravascular blood flow and showed them to be as high as 28% of the mean.     

基于光纤振动的激光散斑抑制方法的研究

为了解决激光显微成像系统中散斑的抑制问题,采用散斑暗区比方法研究了光纤振动对显微散斑图像的影响。实验中采用波长为532nm的激光作为显微系统光源,利用光纤振动对激光显微图像散斑进行抑制;同时采用CCD图像传感采集系统对样品表面进行的显微成像,并对光纤在不同振动电压下的显微图像暗区比进行了分析。结果表明,随着振动电压的增大,图像的散斑暗区比会逐渐减小,当电压为2.6V时,图像散斑暗区比达到5.64%,散斑对比度为4.17%,接近人眼分辨率4%,可达到良好的散斑抑制效果。     

计算光学成像在散射中的应用

自然界中普遍存在光散射现象。如何通过散射介质实现高分辨率成像是光学成像领域亟待解决的重要问题。在早期研究中,多重光散射被认为是雾霾、云层、生物组织等复杂介质成像中的障碍。然而,最近研究表明,散射并不是成像的基本限制:光子在经过多次散射后仍然包含了大量信息。为了深入了解新兴的计算光学成像是如何解决多重光散射问题的,文中主要介绍了波前整形、散斑相关及深度学习等方法在散射成像领域中的研究进展。最新的研究成果表明:波前整形可以实现动态散射介质内部的高分辨率快速聚焦;散斑相关能够利用单帧散斑实现非侵入式成像;基于深度学习的成像技术能恢复出隐藏在光学厚度为13.4的白色聚苯乙烯平板背后的物体。     

激光片光三维传感中提高深度分辨率的方法

提出了两种在激光片光三维传感中降低散斑噪声、提高深度分辨率的方法。第1种方法采用宏观上相同、微观上受物体微结构面元影响的多帧散斑图像叠加,用于三维测量系统的标定。第2种方法利用动态采集方式,使CCD对微结构元进行时间积分,可有效地降低散斑噪声的影响。实验证明,综合利用这两种方式,深度分辨率可以得到有效的提高。     

基于光纤振动的激光散斑控制

散斑噪声的存在使得图像灰度剧烈变化,降低了图像分辨率,影响成像质量。为了控制散斑噪声,使用波长为405nm的激光作为显微系统照明光源,利用音圈电机振动光纤,通过对抛光玻璃显微成像,用CCD图像采集卡采集图像后进行了散斑噪声对比度分析。结果表明,在光纤振动幅度不变、振动频率在4Hz~55Hz内逐渐增加时,图像散斑对比度在0.0326~0.1197范围内逐渐变小;当频率大于51Hz时,图像散斑对比度曲线趋于平稳且对比度在0.0326处获得了最小值,图像清晰,达到良好的散斑控制。     

动态主观散斑的时间相关性研究

根据散射屏移动时动态主观散斑时间相关公式,分析了成像系统主要参数对动态主观散斑时间相关性的影响：一般情况下屏表面参数对散斑的时间相关性影响较小;激光光斑大于成像系统物面分辨斑时,散斑的时间相关性由透镜孔径大小决定;激光光斑小于成像系统物面分辨斑的尺寸时,减小激光光斑尺寸能减弱散斑时间相关性。对于以上结果进行了相关的理论模拟和部分实验验证,通过模拟发现,激光光斑小于成像系统物面分辨斑时,散斑时间相关长度和光斑尺寸大小成正比。结论对于激光投影系统中利用时间平均进行的散斑抑制具有指导意义。     

环形光纤激光器自混合散斑自相关测速的研究

研究了一种基于强度自相关函数的光纤激光器自混合散斑速度测量方法.基于环形激光器光反馈理论,对自混合散斑信号进行自相关分析,推导出自混合散斑信号的自相关频率与表面粗糙物体运动速度之间的关系式.利用构建的环形掺铒光纤(EDF)激光器自混合散斑测速实验系统,对不同速度下的运动物体进行了实验测试,验证了自相关频率与物体运动速度...     

Interventional 4-D C-arm CT perfusion imaging using interleaved scanning and partial reconstruction interpolation

Tissue perfusion measurement during catheter-guided stroke treatment in the interventional suite is currently not possible. In this work, we present a novel approach that uses a C-arm angiography system capable of computed tomography (CT)-like imaging (C-arm CT) for this purpose. With C-arm CT one reconstructed volume can be obtained every 4-6 s which makes it challenging to measure the flow of an injected contrast bolus. We have developed an interleaved scanning (IS) protocol that uses several scan sequences to increase temporal sampling. Using a dedicated 4-D reconstruction approach based on partial reconstruction interpolation (PRI) we can optimally process our data. We evaluated our combined approach (IS-PRI) with simulations and a study in five healthy pigs. In our simulations, the cerebral blood flow values (unit: ml/100 g/min) were 60 (healthy tissue) and 20 (pathological tissue). For one scan sequence the values were estimated with standard deviations of 14.3 and 2.9, respectively. For two interleaved sequences the standard deviations decreased to 3.6 and 1.5, respectively. We used perfusion CT to validate the in vivo results. With two interleaved sequences we achieved promising correlations ranging from r=0.63 to r=0.94. The results suggest that C-arm CT tissue perfusion imaging is feasible with two interleaved scan sequences.     

一种激光搜跟器的光学设计

为提高激光搜跟器对地目标的搜索范围和成像分辨率,提出了一种机载平台下的共孔径激光搜跟器扫搜和跟踪目标的方法,并进行了光学系统的设计。激光搜跟器采用捷联的方式固定于飞行器上,提高了其稳定性;激光的出射和回波的接收,采用共孔径的R-C式反射望远系统实现,缩小了其整体尺寸,并提高了成像分辨率;扫描搜索目标采用双光楔组件实现,并提高了搜索频率和扩大了搜索视场;给出了双光楔旋转角和出射光偏转角之间的关系。设计结果表明,当系统通光孔径为φ300 mm,焦距为2 100 mm时,总体尺寸为685 mm,可扫描搜索视场为±5°,成像视场为±0.08°,成像点弥散斑最大为2.417 μm,系统MTF值在50 lp/mm时大于0.4,满足成像要求;当目标距离为3 km时,可搜索范围达到526 m,可实现对4 m大小目标的成像,成像分辨率为2″。     

光盘信息符统计特性的激光散斑测试

采用激光散斑的方法研究了CD光盘的刻录质量.由于标志光盘信息符的凹凸结构导致了光盘表面微结构的光学粗糙性,光盘不同区域被激光照射后在测量空间形成散斑图像,通过分析光盘不同区域产生的散斑图的统计相关性及对比度值的变化,对光盘的刻录质量进行了定性研究.结果显示,刻录质量好的光盘,其不同区域的散斑相关性好,散斑对比度值高且起...     

激光成像系统图像散斑抑制算法比较

CO2激光相干成像系统具有分辨率高、抗干扰能力强、能三维成像等特点,但其所成图像易受到散斑噪声的污染造成分辨率下降,因此研究适用于此成像系统图像散斑噪声抑制的算法具有重要的实用价值。文中对常用的噪声抑制算法:中值滤波、同态均值滤波和Lee滤波进行了介绍,并将其应用于CO2脉冲激光相干成像系统图像的散斑噪声抑制处理,比较了三种算法的处理结果。结果表明,采用小窗口、不迭代Lee滤波进行处理时,既明显抑制了散斑噪声,又有效保持了图像的边缘信息,所以用它进行激光成像系统图像散斑噪声抑制处理是合适的。     

利用激光散斑成像监测光动力治疗的血管损伤效应

激光散斑衬比成像(LSCI)技术作为一种高时空分辨的血流流速分布监测技术，无需扫描即可实时地全场记录微循环血流的时空变化特性。鸡胚尿囊膜(CAM)是用于在体研究光动力治疗(PDT)血管损伤效应的理想动物模型。以发育10天鸡胚尿囊膜为模型，使用光敏剂——焦脱镁叶绿酸(pyropheophorbide acid，pyro-acid)，激光照射波长为656．5nm，光照射功率为40mW／cm^2，研究了肿瘤周围血管在激光照射下的血管管径变化和血流速度分布变化。研究表明，通过对血管管径和血流速度的监测，激光散斑衬比成像技术可以用于评估光动力治疗过程中的肿瘤周围血管损伤效应。     

Research on dynamic measurement method of speckle in laser display

Laser display technology is the most promising display technology in the market and is widely used in many fields. However, laser speckle has been troubling the application and expansion of this technology in some fields. In order to better evaluate the speckle, speckle measurement methods must be studied. In this study, a dynamic measurement method for laser speckles is proposed according to the optical superposition characteristics of speckle, which can reduce the influence of non-coherent factors on the speckle measurement results. The feasibility of the dynamic speckle measurement method is verified by designing an experimental scheme.     

Near‐Infrared IIb Fluorescence Imaging of Vascular Regeneration with Dynamic Tissue Perfusion Measurement and High Spatial Resolution

Real‐time optical imaging is a promising approach for visualizing in vivo hemodynamics and vascular structure in mice with experimentally induced peripheral arterial disease (PAD). The application of a novel fluorescence‐based all‐optical imaging approach in the near‐infrared IIb (NIR‐IIb, 1500–1700 nm emission) window, for imaging hindlimb microvasculature and blood perfusion in a mouse model of PAD is reported. In phantom studies, lead sulfide/cadmium sulfide (PbS/CdS) quantum dots show better retention of image clarity, in comparison with single‐walled nanotube (SWNT) NIR‐IIa (1000–1400 nm) dye, at varying depths of penetration. When systemically injected to mice, PbS/CdS demonstrates improved clarity of the vasculature, compared to SWNTs, as well as higher spatial resolution than in vivo microscopic computed tomography. In a mouse model of PAD, NIR‐IIb imaging of the ischemic hindlimb vasculature shows significant improvement in blood perfusion over the course of 10 days (P < 0.05), as well as a significant increase in microvascular density over the first 7 days after induction of PAD. In conclusion, NIR‐IIb imaging of PbS/CdS vascular contrast agent is a useful multifunctional imaging approach for high spatial resolution imaging of the microvasculature and quantification of blood perfusion recovery.     

直接成像技术在PCB中的应用

电子产品日趋小型化、轻量化、多功能化，使电路板线路密度增加，从而对电路板的制作技术有了更高的要求，普通的接触曝光成像技术不能满足高密度电路的要求，激光直接成像（LDI）技术正迎合了精细线路的要求，而在PCB制作中得到应用。介绍了LDI的成像原理、存在的优缺点及其在PCB制作中的应用。