基于液晶自适应光学的高对比度视网膜微血管成像

发布时间：2018-10-17 21:32

【摘要】：通过视网膜微血管形态检查可以早期诊断内分泌疾病。但是，由于人眼像差的存在，使临床所用检眼镜的分辨率大幅下降，不能直接看到10μm以下的微细血管。自适应光学技术能够实时补偿人眼像差，得到接近衍射极限的视网膜视觉细胞图像，但对视网膜微细血管成像时还存在一些问题。本论文针对准确定位微细血管困难、图像对比度难以达到临床要求等问题，结合人眼的光学特性，进行了一系列光学系统的创新设计。采用视标盯视方法进行眼底方位定位。根据人眼焦深、调节误差、视觉锐度和对颜色的敏感度，设计视标的位置、形状、照明波长等：确定眼前1D处的视标满足准确性、普适性的要求；设计马耳他十字视标，调节支臂可满足不同视力的人眼盯视；采用人眼最敏感的绿光照射视标，有利于提高人眼盯视能力。根据视网膜结构，定位方法分三步：1）选择小凹中心为定位的基准，2）横向定位之后，按照系统放大倍率，将成像相机进行轴向位移，聚焦到位于视网膜内部几层的血管，3）找到较粗血管后，可沿血管走势有意识控制横向定位，直至寻找到10μm以下微细血管。设计了具有微细血管搜寻定位的自适应光学成像系统。根据视网膜血管的吸收波长，，确定了高对比度视网膜血管的成像方法：1）先用785nm红外光搜寻，以避免绿光长时曝光对人眼的强烈刺激，2）再使用561nm绿光数毫秒曝光成像。通过理论计算得到具体的有利于提高对比度的途径。利用血液与周围组织结构偏振性的差异，设计液晶偏振自适应光学系统，利用微细血管的消偏光成像，对比度达到0.25，较原来提高约1.2倍。针对实际光路中由于光学器件的加工和光学系统装调中的误差，极限分辨率远远达不到理想设计值的问题，设计简易化自适应光学系统，大大减少所使用的光学元器件的个数。在保证系统校正功能的基础上，提高了系统的能量利用率和调制传递函数。利用图像配准与叠加消除噪声以提高对比度，使得获得的图像具有更高的临床使用价值。
[Abstract]:Early diagnosis of endocrine diseases can be made by microvascular morphology of retina. However, due to the existence of human aberration, the resolution of ophthalmoscope used in clinic is greatly reduced, and the fine blood vessels below 10 渭 m can not be seen directly. Adaptive optics can compensate human eye aberration in real time and obtain retinal visual cell images close to the diffraction limit. However, there are still some problems in retinal microvascular imaging. In this paper, a series of innovative design of optical system is carried out based on the optical characteristics of human eyes in view of the difficulty of accurately locating fine blood vessels and the difficulty of image contrast meeting the clinical requirements. The eye fundus orientation was carried out by using the method of visual standard staring. According to the depth of human eye focus, adjustment error, visual acuity and sensitivity to color, design the position, shape, lighting wavelength, etc.; determine that the visual standard at 1D in front meets the requirements of accuracy and universality; design the Maltese cross visual standard, Adjusting the supporting arm can satisfy the different visual acuity of human eyes, and using the most sensitive green light to illuminate the visual standard is helpful to improve the ability of human eyes to stare. According to the structure of the retina, the localization method is divided into three steps: 1) selecting the fovea center as the datum for the location, 2) after the lateral positioning, the imaging camera is rotated in axial direction according to the magnification rate of the system. Focusing on the vessels located in several layers of the retina, 3) after finding the thicker vessels, we can consciously control the lateral orientation along the trend of the vessels until we find the microvessels below 10 渭 m. An adaptive optical imaging system with micro vascular search and location is designed. According to the absorption wavelength of retinal vessels, the imaging methods of high contrast retinal vessels were determined as follows: 1) search with 785nm infrared light first to avoid strong stimulation of human eyes by long exposure of green light, 2) then use 561nm green light in millisecond exposure imaging. Through theoretical calculation, a specific way is obtained to improve the contrast. Based on the polarization difference between blood and surrounding tissue structure, a liquid crystal polarization adaptive optical system is designed. The contrast is 0.25, which is about 1.2 times higher than that before, using depolarizing imaging of fine blood vessels. In order to solve the problem that the limit resolution is far from the ideal design value due to the processing of optical devices and the errors in optical system installation in the practical optical path, a simplified adaptive optical system is designed, which greatly reduces the number of optical components used. On the basis of ensuring the correction function of the system, the energy utilization ratio and modulation transfer function of the system are improved. Image registration and superposition are used to eliminate noise in order to improve the contrast and make the images have higher clinical value.
【学位授予单位】：中国科学院研究生院(长春光学精密机械与物理研究所)
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O439;R774.1

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