近红外光谱无创血糖检测中有效信号提取方法的研究

糖尿病严重危害人类健康,无创血糖检测是医患双方的期望。人体生理背景成分复杂、易变,各种组织信息混杂,导致直接测量人体的近红外光谱很难真实反映血液中血糖浓度变化信息。提出血流容积差光谱相减法,即利用血流容积一直在变而人体组织背景和血液成分含量短时间不变的事实,通过相似背景扣除,有效消除人体组织背景干扰,获得反映血液成分信息的有效光谱信号。为验证方法的有效性,自行研制相关实验系统,获得系统噪声好于20 μAU,并在波长1 250 nm处取得信噪比为20 000∶1的有效光谱信号,阐明现有条件下血流容积差光谱相减法在近红外无创血糖检验临床应用的可行性和优势。     

双散射光合成场动态散斑的统计性质

本文研究了在两束高斯光束照明条件下,由旋转散射体产生的双散射光合成的远场动态散斑的统计性质.这种动态散斑的统计性质由它的强度涨落的空-时相关函数描述.文中推导了这个函数的解析表达式,并采用了光子计算及光子相关技术,从实验上证实了这个表达式的正确性.     

大气压介质阻挡放电中的自组织斑图结构

采用水作为电极,对大气压介质阻挡放电中的自组织斑图结构进行了研究,观测到了规则的斑图结构(包括准六边形斑图和条带状斑图)和不规则的斑图结构.实验发现斑图中放电丝的密度随着电介质层厚度的增加及放电气隙宽度变大而减小,而随外加电压及频率增大而增大.采用空间相关函数的方法分析了准六边形斑图结构中的放电丝分布与驱动电源电压的关系 关键词： 介质阻挡放电 自组织斑图 放电丝密度 空间相关函数     

超声调制介质中漫散射光自相关性质研究

研究了超声调制随机介质中漫散射光自相关性质,推导出均匀无限介质中有超声场调制时漫散射光时间自相关函数的表达式,讨论了调制参数、调制幅度及其衰减与超声参数、光散射参数等的关系.用Monte Carlo方法研究了随机介质中隐含异物成像的可行性.结果表明,正常生物组织和病变生物组织的超声调制自相关函数有明显的差别,该方法为光学医学诊断提供了一种新参考 关键词： 自相关 漫散射光 超声调制 光学成像     

基于数字散斑相关法的岩石材料力学性能的测试

岩石在外力作用下会发生形变,发现和了解岩石材料的形变、应力分布等对避免灾害会起到重要的预警作用。采用高精度的数字散斑相关技术,对岩石材料形变、应力和应变进行了非接触式测量。为验证实验结果的有效性,电阻应变计贴附于采集区附近并且实验结果与电测结果吻合较好。表明数字散斑相关测量技术能够用于岩石等材料的形变检测,预报变形信息,结果可以定量和定性显示。     

基于二维相关中红外光谱技术的无创血糖检测特异性研究

葡萄糖的特异性是实现血糖浓度检测的前提,也是论证一种血糖检测方法可行性的基础。二维相关光谱技术以其高分辨率和便捷的时序规则(Noda规则)两大优势被广泛地应用在分子间(内)反应、物质相变以及物质信息提取等研究领域。旨在应用二维相关光谱技术验证中红外光谱法无创血糖检测技术的葡萄糖特异性,首先通过分析各种离体溶液样本的二维相关光谱证明方法的理论可行性,然后开展了人体手指的中红外ATR光谱采集实验,参考OGTT方法调节实验过程中人体的血糖水平,并运用二维相关光谱技术验证所得人体光谱中的葡萄糖特征信息,从而论证中红外光谱无创血糖检测技术的可行性。     

近背向散射能量空间分布的时间分辨测量技术

基于神光Ⅲ原型激光装置上建成的近背向散射诊断系统,设计了一种可探测近背向散射能量空间分布的时间过程的采集方法,并通过静态实验对该方法的可行性进行了验证。结果表明:通过一维转二维传像束,将二维图像记录成一维信息,然后通过数据后处理还原成二维图像信息的方法可以实现能量空间分布的时间分辨测量。将该方法用于近背向散射光诊断系统,可以得到近背向散射光能量空间分布随时间变化的信息,为深入分析激光等离子体相互作用实验中近背向散射光构成及变化过程提供重要数据。     

预测搜索算法在图像相关中的应用

数字散斑相关方法在亚像素测量过程中运算量大,在对实时性要求较高的系统中该方法的应用受到了限制。提出了一种原理简单、搜索速度快、精度高的预测搜索算法,介绍了预测搜索算法的原理,并给出预测位移的公式。通过实验验证了对算法的精度、效率和鲁棒性,说明对数字散斑相关方法进行优化后,既不损失亚像素位移的计算精度又提高了图像处理的效率。     

基于直接检测相干光时域反射计的高分辨率分布式光纤传感技术

研究了基于瑞利散射的高性能定量检测分布式光纤传感技术。在相位敏感光时域反射计(Φ-OTDR)的基础上,用窄线宽激光器和微波电光调制实现对光频移的精确控制,构成直接检测相干光时域反射计(COTDR)传感系统。通过分析光频移产生的传感光纤瑞利散射光干涉图样的变化,得到了传感量(温度或应变)的定量信息。对直接检测COTDR传感系统进行了理论分析,并进行了COTDR工作过程和散射信号相关特性的仿真分析,验证了高分辨率分布式光纤传感原理。在此理论分析基础上,采用微波电光调制得到了可变光频移,组建了直接检测COTDR实验系统,实现了25 km分布式光纤温度传感实验,可测量到25 km光纤末端0.1℃的温度变化。     

数字图像相关中的散斑区域自动提取研究

数字图像相关测量中,相关计算前会人工选取散斑区域进行区域限定。随着工业自动化的发展,面对散斑区域形状越来越复杂以及大量散斑图片的测量需求,找到一种散斑区域自动提取方法至关重要。本文根据散斑的特征,对比多种常规边缘检测方法,提出了一种基于二阶梯度熵函数的散斑区域自动提取判定函数,并通过分析不同的散斑图片,确定了最佳子区熵尺寸区间以及在不同散斑图中的自适应阈值区间,最终通过连通区域分割完成对散斑区域的自动提取。文中采用实际拍摄的散斑图对该方法进行验证,实验结果表明:子区熵尺寸取10 pixel以上,该算法对散斑区域表现敏感;自适应阈值取图中最大梯度熵值的Q-1. 25至Q范围内时,可以将散斑区域与背景区域有效分割。基本能完成对散斑区域的自动提取,达到了相关计算前散斑区域选择的目的。     

Improvement of ultrasound speckle image velocimetry using image enhancement techniques

Ultrasound-based techniques have been developed and widely used in noninvasive measurement of blood velocity. Speckle image velocimetry (SIV), which applies a cross-correlation algorithm to consecutive B-mode images of blood flow has often been employed owing to its better spatial resolution compared with conventional Doppler-based measurement techniques. The SIV technique utilizes speckles backscattered from red blood cell (RBC) aggregates as flow tracers. Hence, the intensity and size of such speckles are highly dependent on hemodynamic conditions. The grayscale intensity of speckle images varies along the radial direction of blood vessels because of the shear rate dependence of RBC aggregation. This inhomogeneous distribution of echo speckles decreases the signal-to-noise ratio (SNR) of a cross-correlation analysis and produces spurious results. In the present study, image-enhancement techniques such as contrast-limited adaptive histogram equalization (CLAHE), min/max technique, and subtraction of background image (SB) method were applied to speckle images to achieve a more accurate SIV measurement. A mechanical sector ultrasound scanner was used to obtain ultrasound speckle images from rat blood under steady and pulsatile flows. The effects of the image-enhancement techniques on SIV analysis were evaluated by comparing image intensities, velocities, and cross-correlation maps. The velocity profiles and wall shear rate (WSR) obtained from RBC suspension images were compared with the analytical solution for validation. In addition, the image-enhancement techniques were applied to in vivo measurement of blood flow in human vein. The experimental results of both in vitro and in vivo SIV measurements show that the intensity gradient in heterogeneous speckles has substantial influence on the cross-correlation analysis. The image-enhancement techniques used in this study can minimize errors encountered in ultrasound SIV measurement in which RBCs are used as flow tracers instead of exogenous contrast agents.     

Frame-rate analysis of arterial blood flow in human and rat using laser speckle image sensing

In imaging of blood flow by means of a laser speckle technique, we have proposed so far an estimation parameter based on the spatial contrast of speckle patterns observed for the blood flow in skin tissue and a blood vessel. This parameter enable us to image a relative blood flow distribution from a single speckle pattern, thus, it analyzes the blood flow with a frame-rate of an imaging device used. In this study, we investigated availability of this parameter for detecting changes in arterial blood flow caused by medication and cold stimulation to the skin tissue. Experiments were conducted for an anesthetized rat and a human wrist to confirm the feasibility of the present parameter.     

Effects of red blood cell aggregates dissociation on the estimation of ultrasound speckle image velocimetry

Ultrasound speckle image of blood is mainly attributed by red blood cells (RBCs) which tend to form RBC aggregates. RBC aggregates are separated into individual cells when the shear force is over a certain value. The dissociation of RBC aggregates has an influence on the performance of ultrasound speckle image velocimetry (SIV) technique in which a cross-correlation algorithm is applied to the speckle images to get the velocity field information. The present study aims to investigate the effect of the dissociation of RBC aggregates on the estimation quality of SIV technique. Ultrasound B-mode images were captured from the porcine blood circulating in a mock-up flow loop with varying flow rate. To verify the measurement performance of SIV technique, the centerline velocity measured by the SIV technique was compared with that measured by Doppler spectrograms. The dissociation of RBC aggregates was estimated by using decorrelation of speckle patterns in which the subsequent window was shifted as much as the speckle displacement to compensate decorrelation caused by in-plane loss of speckle patterns. The decorrelation of speckles is considerably increased according to shear rate. Its variations are different along the radial direction. Because the dissociation of RBC aggregates changes ultrasound speckles, the estimation quality of SIV technique is significantly correlated with the decorrelation of speckles. This degradation of measurement quality may be improved by increasing the data acquisition rate. This study would be useful for simultaneous measurement of hemodynamic and hemorheological information of blood flows using only speckle images.     

Optical coherence Doppler tomography quantifies laser speckle contrast imaging for blood flow imaging in the rat cerebral cortex

A dual-imaging modality is demonstrated for high-resolution quantitative imaging of local cerebral blood flow in the rat cortex by combining simultaneous spectral-domain Doppler optical coherence tomography (SDOCT) and full-field laser speckle contrast imaging (LSCI). Preliminary studies in tissue flow phantom and cocaine-induced cerebral blood flow changes indicated that by correlating coregistered cortical arterial blood flow, the relative measurement of flow changes by LSCI could be accurately calibrated by the absolute flow imaging provided by SDOCT (least square fit, r(2) approximately 0.96). Quantitative LSCI of cerebral blood flow is crucial to the quantitative analyses of the spatiotemporal hemodynamics of functional brain activations and thus improved understanding of neural process.     

Blood Flow Analyses of Skin Tissue Under the Sacrum Using Laser Speckle Flowgraphy

A new version of the Laser Speckle Flowgraphy was developed to study the dependence of the blood flow of the skin tissue under the sacrum and the supporting pressure against the sacrum. The measuring unit consists of the laser diode, imaging system, line sensor, scanning mirror, and one-board microcomputer. The speckle signal is analyzed and sent to a personal computer, where the blood flow in a tissue area of 19 cm × 25 cm is evaluated and displayed on a 2-D color map. It was found that the blood flow in the skin tissue sharply decreased under the sacrum when it was supported by a hard surface, while the decrease became negligible when the surface was replaced by a soft airbag.     

半导体激光器的自混合散斑干涉测量流体速度

提出了一种简便的激光自混合散斑干涉测量流体速度的方法。根据散斑和法布里-珀罗腔的理论,提出了半导体激光器的自混合散斑干涉模型。研究了流体运动时在半导体激光器内产生的自混合散斑干涉效应(SMPI),给出了激光器输出增益的变化及其概率密度分布。得到了激光自混合散斑干涉平均频率与流体速度之间的关系。模拟计算和实验结果验证了这个关系。利用散斑干涉的平均频率与流体速度的关系测量了高分子材料溶液的速度,并在溶液浓度和背景光变化时,对流体速度进行了测量、比较和分析。实验表明。在溶液浓度不太低时,测量误差小于8％。     

New Laser Speckle Flowgraphy System Using CCD Camera

A new technique is developed to visualize the blood flow map of the human retina using laser speckle phenomena. Despite use of an ordinary CCD camera as the detector, the performance of laser speckle flowgraphy system for the analysis of ocular blood circulation is greatly improved to achieve higher resolution and a wider field of view for blood flow mapping. It is shown that the quality of the blood flow map is influenced by the sampling format of the pixel points in the space- and time-varying speckle field.     

Enhancement in sensitivity of a blood perfusion parameter for frame-rate analysis of bio-speckle image

We have previously presented a blood perfusion parameter by means of the spatial contrast of speckle patterns observed for blood perfusion in skin tissue and a blood vessel. This parameter permits us to visualize a relative blood perfusion distribution from a single speckle pattern. Therefore, it can estimate the blood perfusion with a frame rate of an imaging device employed. This parameter is, however, dependent on the speckle size and the condition of image processing of speckle patterns. In the present study, we estimated this condition with relation to the speckle size for obtaining high sensitivity and good linearity of the parameter to the blood perfusion. Experiments were conducted for ground-glass model, flow model and human wrist to investigate perfusion sensing characteristics of the present parameter.

     

用激光散斑跨零法监测皮肤血流变化

由皮肤散射形成的动态激光散斑携带了皮肤血流的信息.由于来自运动着的红血球的散射光两次经过皮肤表面,因而受到三次随机调制.本文根据串级散斑的快速时间涨落的特点,提出了用激光散斑的胯零率测量皮肤血流的新方法,给出了跨零率与血流速度参数之间的关系式和实验结果.     

Improvement of estimation parameters in bio-speckle blood flow imaging

Two novel estimation parameters are proposed for bio-speckle blood flow imaging in skin tissue with reducing effects of a speckle contrast and random noises. Estimation parameters are introduced to reduce the effect of the speckle contrast on the sensitivity of the blood flow sensing and to eliminate an offset component due to random noises superimposed on the speckle images. Experiments were conducted for a sample model using ground-glass plates, human vein and finger to confirm the feasibility of the proposed parameters.