激光散斑衬比度成像中的噪声影响及修正方法

发布时间：2018-05-19 22:26

本文选题：激光散斑衬比度成像 + 光散粒噪声　；参考：《南京理工大学》2017年硕士论文

【摘要】：激光散斑衬比度成像方法作为一种可用于血流监测的光学成像方法,具有非接触、时空分辨率高、简易性等优点,已经在视网膜和脑皮层血流监测领域有所应用。然而成像系统中的噪声影响以及生物组织中多次散射对散斑动态变化影响的研究尚不深入,还有诸多问题需要解决。本文从理论分析、数值模拟和实验测量三方面对激光散斑衬比度成像中的CCD噪声影响展开了讨论。鉴于激光散斑成像系统中的光散粒噪声作为CCD固有噪声难以消除,亦是成像系统的主要噪声来源,文中首先对光散粒噪声对衬比度测量的影响进行了理论分析,认为由于光散粒噪声的存在使得衬比度测量结果偏差值会随着光强的减小而增大。之后,运用基于变量相关的动态散斑模拟方法得到了散斑图像,并对模拟散斑图像进行衬比分析,从而验证了理论分析的正确性。进而实验结果表明:光散粒噪声在弱光条件下对衬比度测量准确性的影响较大;且通过实验测量获得了表征CCD散粒噪声的参数——转换增益γ。结合光散粒噪声和暗噪声给出了散斑衬比度CCD噪声影响的修正公式。考虑到CCD噪声修正方法可应用于多次散射的散斑衬比度成像研究领域,因而从理论公式推导和实验研究两方面对其进行研究。首先根据扩散相关谱理论,推导了基于多次散射理论的扩散散斑衬比度的理论计算公式,给出了扩散散斑衬比度与曝光时间、光源-探测器距离和布朗运动扩散系数关系的解析解。之后,构建了扩散散斑衬比度成像的实验装置,并对实验结果修正了散粒噪声影响,进而分别根据两种关系:曝光时间一定时,衬比度随光源-探测器距离变化的关系;光源-探测器距离一定时,衬比度随曝光时间变化的关系,通过拟合求解得到扩散系数值,并与理论值进行比较,从而验证了利用扩散散斑衬比度成像方法进行定量测量的有效性。本文的研究结果可为提高激光散斑衬比度成像方法的测量准确性提供参考。
[Abstract]:As an optical imaging method for blood flow monitoring, laser speckle contrast imaging has many advantages, such as non-contact, high spatial and temporal resolution, simplicity and so on. It has been applied in the field of retinal and cerebral cortex blood flow monitoring. However, the effects of noise and multiple scattering in biological tissues on the dynamic change of speckle are not well studied, and there are still many problems to be solved. In this paper, the influence of CCD noise in laser speckle contrast imaging is discussed from three aspects: theoretical analysis, numerical simulation and experimental measurement. As the inherent noise of CCD is difficult to eliminate in the laser speckle imaging system, it is also the main noise source of the imaging system. In this paper, the influence of the laser speckle noise on the contrast measurement is analyzed theoretically. It is considered that the deviation value of contrast measurement results will increase with the decrease of light intensity due to the existence of particle noise. After that, the dynamic speckle simulation method based on variable correlation is used to obtain the speckle image, and the contrast ratio of the simulated speckle image is analyzed, which verifies the correctness of the theoretical analysis. The experimental results show that the accuracy of contrast measurement is greatly affected by the light shot noise under the condition of low light, and the parameter-conversion gain 纬 which characterizes the CCD shot noise is obtained by experimental measurement. The correction formula of speckle contrast ratio CCD noise is given by combining the light speckle noise and dark noise. Considering that the CCD noise correction method can be used in the field of speckle contrast imaging with multiple scattering, the theoretical formula and the experimental study are studied. Based on the diffusion correlation spectrum theory, the theoretical formula of diffusive speckle contrast ratio based on multiple scattering theory is derived, and the diffusive speckle contrast ratio and exposure time are given. The analytical solution of the relation between the distance between the light source and the detector and the diffusion coefficient of the Brownian motion. Then, an experimental device for diffusive speckle contrast imaging is constructed, and the effect of shot noise on the experimental results is corrected, which is based on two relationships: the relation of contrast ratio with the distance between light source and detector when the exposure time is constant; When the distance between the light source and the detector is constant, the contrast ratio varies with the exposure time, and the diffusion coefficient is obtained by fitting, and compared with the theoretical value. The effectiveness of quantitative measurement using diffusion-speckle contrast imaging method is verified. The results of this paper can be used to improve the accuracy of laser speckle contrast imaging.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN249

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