【作者】 邱建军；

【导师】 骆清铭；

【作者基本信息】 华中科技大学 ， 生物医学工程， 2010， 博士

【摘要】 激光散斑衬比成像方法以其快速、高分辨、无需扫描即可实现大范围内二维流速成像的特点,在脑组织、皮肤、眼底视网膜、关节以及肠系膜等生物组织血流检测中取得了重要应用,为反映生物组织功能活动、揭示重大疾病产生机制以及药效评价提供了重要的研究工具。同时,该方法以其快速、非接触、系统结构简单等特点在种子活力快速检测中具有重要的潜在应用价值,为农业生产中选种、育种以及作物储藏研究提供了潜在的检测手段。然而激光散斑衬比成像方法无论在方法学还是应用层面都存在诸多问题需要解决、改进和深入研究。因此,本文选择从方法学和应用两方面对激光散斑衬比成像方法展开研究。在方法学层面,从理论计算、数值模拟和模型实验等方面对激光散斑衬比成像中涉及的若干重要问题展开探讨,包括：空间分辨率与衬比测量准确性的关系；成像系统噪声对衬比测量准确性的影响；速度测量线性范围；散斑尺寸对静态散斑衬比和动态散斑衬比的影响；几种衬比分析方法性能的比较。在应用层面,对激光散斑衬比成像方法应用于种子活性检测的有效性进行实验验证,对几种激光散斑数据分析方法的性能及各自的成像条件进行比较和分析。本文取得的主要研究结果如下：(1)针对现有的激光散斑模拟方法的局限性,发展了基于变量相关的时间积分动态散斑模拟方法,并将该方法与模型实验相结合,对激光散斑衬比成像系统性能进行了分析：指出在保证速度测量准确性的前提下,当不考虑CCD像素尺寸对空间分辨率影响时,激光散斑衬比成像空间分辨率一般为光学系统最高分辨率的一半；CCD噪声中光散粒噪声和直流噪声和对弱光下的衬比测量准确性影响较大,在平均光强低于200 counts时衬比测量误差可达10%以上；布朗运动的差异导致成像系统对不同散射样品的速度测量线性范围不同。(2)研究了散斑尺寸对激光散斑衬比成像的影响。提出了局域静态散斑空间衬比与散斑尺寸和空间窗长度关系的近似表达式,为激光散斑衬比成像中合理的散斑尺寸的选取提供了指导；对动态散斑的研究表明,不同散斑尺寸下CCD像素空间积分效应对空间衬比和时间衬比的影响具有等价性,但散斑尺寸对空间域上有效统计像素数的影响较大,而对时间域上有效统计像素数的影响较小,从而解释了激光散斑衬比成像在血流速度测量中,时间衬比分析方法比空间衬比分析方法需要更少的统计像素数即可获得准确的衬比均值的原因。(3)比较了已有的几种基于时间统计与空间统计相结合的衬比分析方法。数值模拟和动物实验研究均表明,时空联合衬比分析方法(stLASCA)的衬比均值最大测量误差约5%,而时间平均的空间衬比分析方法(sLASCA)和空间平均的时间衬比分析方法(tLASCA)的衬比均值最大测量误差为13%以上,而三种方法的统计噪声相当,表明在各态历经条件下stLASCA方法统计准确性高于sLASCA和tLASCA方法。(4)对吸胀的玉米种子散斑图像处理结果表明,激光散斑衬比分析方法(sLASCA和tLASCA)和激光散斑时间微分方法可在10s以内完成单个种子活力检测,获得的图像对比度分别为0.26、0.32和0.57。对发芽初期的玉米种子散斑图像处理结果表明,激光散斑时间微分方法在5 ms曝光时间下获得的图像对比度最高,但难以获取运动速度的细节差异,而激光散斑衬比分析方法在500 ms以上曝光时间下,可以明显显示胚轴与其他部位的流速差异。更多还原

【Abstract】 Laser speckle contrast imaging (LSCI) has been widely used in detecting blood flow changes in brain, skin, retina, arthrosis and mesentery with the advantages of fast processing, high spatial and temporal resolution, full-field imaging without scanning, providing important tool in investigating functional activities of tissues, exploring mechanisms of diseases and evaluating drug efficiency. Meanwhile, LSCI has significant potential application in detecting seed vigour with the advantages of fast imaging, non-contact and simple system structure, thus provides potential tool for seed breeding and crop store. However, many problems deserve addressed, improved and investigated intensively, either in the methodology and the application aspects of LSCI.Therefore, this thesis investigates problems in LSCI in both the methodology and the application aspects. In the methodology aspect, we investigate some important problems in LSCI through theoretical arithmetic, numerical simulation and phantom experiments, including:the relation between spatial resolution of LSCI and statistical accuracy; impact of noises in imaging system on statistical accuracy of speckle contrast; linear response range of LSCI in speed estimation; impact of speckle size on static and dynamic speckle contrast values; comparisons among the existing speckle contrast analysis methods. In the application aspect, we verify the vaidity of LSCI in seed vigour test, and investigate the performances of some laser speckle image processing methods and the optimum imaging conditions for these methods. The main results of this thesis include:(1) To overcome limitations of the existing laser speckle simulation methods, we develop a time-integrated dynamic image speckle simulation method based on copula. Combining this method with phantom experiments, we obtain the following results:We point out that in the precondition of maintaining statistical accuracy, spatial resolution of LSCI can only be as high as the half of the maximum spatial resolution of the optical imaging system; Shot noise and DC noise have significant impacts on the statistical accuracy of speckle contrast under weak light illumination. The relative error in speckle contrast can be higher than 10% when the mean intensity is lower than 200 counts. Differences in Brownian motion lead to linear response range of LSCI for different scattering samples.(2) We investigate impacts of speckle size on LSCI. We present an approximative relation among local speckle contrast of static speckle, speckle size and length of spatial window, providing guidance for selecting the optimum speckle size in LSCI. Investigations on dynamic speckle show that spatial integration effect of CCD pixels has equal impact on spatial and temporal contrast. However, speckle size significantly affects effective statistical numbers in spatial domain, but has little impact on effective statistical numbers in temporal domain, which explains why temporal contrast analysis requires fewer statistical numbers than spatial contrast analysis does to achieve accurate speckle contrast.(3) We compare the existing speckle contrast analysis methods whih are based on combination of spatial and temporal statistics. Both simulation and animal experiment results show that the maximum relative error in contrast for spatio-temporal speckle contrast analysis method (stLASCA) is 5%, but such measure can be higher than 13% for both temporal averaged spatial speckle contrast analysis method (sLASCA) and spatial averaged temporal speckle contrast analysis mehotd (tLASCA). The statistical noises of these three methods are in the same level. The above results suggest that stLASCA achieves higher statistical accuracy than sLASCA and tLASCA do.(4) Image processing results for the speckle images of soaked corn seeds show that LSCI (specifically sLASCA and tLASCA) and laser speckle time-difference imaging method achieve fast seed vigour detection within 10 s, with image contast of 0.26,0.32 and 0.57, respectively. Image processing results for the speckle images of corn seed in early germination state show that the laser speckle time-difference imaging method achieves the highest image contrast when setting exposure time to 5 ms, but it is unable to differentiate the detailed differences in speeds. On the contrary, difference in flow speeds between hypocotyls and other parts of the embryo can be discriminated using LSCI when setting exposure time to 500 ms and higher.更多还原