基于液晶自适应光学的高对比度视网膜血管成像

	基于液晶自适应光学的高对比度视网膜血管成像
	刘瑞雪
学位类型	博士
导师	宣丽
	2014-07
学位授予单位	中国科学院大学
学位专业	光学工程
摘要	通过视网膜血管形态可以早期诊断内分泌疾病的发生，因此对眼底成像是许多疾病检查必不可少的一步。但是传统检眼镜由于人眼像差的存在，分辨率不高，不能及时看到血管细微的变化。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图像。本课题组也使用液晶自适应光学系统成功得到了高分辨率的视觉细胞图像。但对人眼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、没有专门用于血管成像自适应光学系统、图像对比度还难以达到临床应用等问题，结合人眼的光学特性，进行了一系列光学系统的创新设计。针对非麻痹人眼，采用视标令人眼盯视。根据人眼焦深、调节误差、视觉锐度和对颜色的敏感度，确定和设计视标的位置、形状、照明波长等方面。确定眼前1 D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明，即便有微弱的绿光照射视标，人眼也能敏锐的分别出来，有利于提高盯视能力。根据视网膜结构，确定整个定位方法，分三步：1）选择中心凹最中心为定位的基准， 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，此即轴向等位的过程。3）找到血管位置后，可沿血管的走势有意识控制横向的定位，以便于寻找病灶位置，也有益于后期血管的拼接和处理。讨论分析了这三步定位的准确度，并在光路上进行新的设计，保证系统能达到足够的精度。设计了具有微细血管搜寻定位的自适应光学成像系统。根据血管的分布特征，设计能够实现大范围搜寻血管的盯视系统。根据视网膜血管的光学特性，设计探测与成像光源分离的照明系统。为了达到较好的成像效果,必须实现光源与成像相机联动。根据统计的人眼眼轴数据，计算系统的轴向放大倍率，确定光源和相机移动的范围和精度，并以此标准选择合适的位移台。最后实现了眼底视网膜血管追迹成像。视标引导的血管追迹成像可有针对性沿血管走势确定下一幅图像的位置，成功获得了沿血管轨迹行进的图像。但这种方法也需要被测者的配合，为此，设计眼底扫描成像系统，作为人眼盯视系统的补充，并成功实现了对视网膜血管的扫描成像。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，基本达到临床使用的要求，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的设计值的问题，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。根据所获得视网膜血管图像，采用多种图像处理方法提高对比度。利用图像配准与叠加消除噪声以提高对比度，依据血管流动构建血管形态，使得获得的图像具有更高的临床使用价值。
其他摘要	Fundus examination is a necessary step to diagnos many diseases, for that the morphology of retinal vessels can early represent many endocrine diseases. However, due to the existence of ocular aberrations, the resolution of the traditional ophthalmoscope is not so high to observe changes of vascular subtle timely. Adaptive optics is a novel technology to compensate aberrations of human eye for retinal imaging, which can reach close to the diffraction limit. This research group has been employed a liquid crystal adaptive optics system successfully for high resolution imaging of retinal photoreceptor cells. However, there are still some problems on human vascular imaging, including accurate positioning of micro vascular difficulties, not specifically for vascular imaging adaptive optics system, the image contrast is difficult to achieve the clinical application. In this paper, combined with the optical properties of the eye, several measures would be taken on the innovation design a series of optical system. For non-paralysis eye, a target was employed for eyes staring. According to human focal depth, the eye accommodation error, visual acuity and color sensitivity, the visual target location, shape, illumination wavelength were identified and designed. The distance of 1 D target from the human pupil met the accuracy requirements of the system. The design of Malta cross target shape, regulating arm can meet different visual acuity eyes stare. The most sensitive wavelength is green lighting. Even if a faint green light was illuminated to the target, the human eye can also clearly distinguish details, which is beneficial to improve the ability to stare. Based on retinal structures, the location method was determined to divide into three steps: 1) selecting foveal most center positioning reference, 2) lateral positioning, in accordance with the system magnification, the imaging camera axial displacement, focusing in the inner layers of the retina blood vessel; this is a process of axial. 3) Find the vessel position, along the vascular trend conscious control of lateral positioning, in order to find the location of the lesion, splicing and processing also has the benefit of late vascular. An adaptive optical imaging system with micro vascular searching and locating was designed. According to the distribution characteristics of vessels, a stare system can realize large range for searching vessels. According to the optical characteristics of retinal blood vessels, the illumination system contains two sources, including detection and imaging light source. In order to achieve good imaging results, the linkage of light source and camera should be realized. With the analyzed statistics of the human eye axis data and calculated axial magnification, the movement of source and camera can be confirmed accurately. Specific ways to improve images contrast had been theoretical calculated and discussed. Using the difference polarization characteristics between blood and other tissues, a polarization liquid crystal adaptive optics system had been designed. With the help of polarized light imaging of micro blood vessels, the imaging contrast can be improved to 0.25, which was increased by about 1.2 times and basically reached the requirements for clinical use. In view of the actual optical path due to the processing and optical devices installed in the resolution limit error adjustment, as far from the ideal design value, design of simple adaptive optical system, greatly reduce the number of optical components used in the. Based on obtained retinal vascular images, a variety of image processing methods were used for improving contrast. Image registration was employed for noise elimination to improve contrast. In accordance with the blood flow, the vascular morphology was reconstructed, which made the obtained images with higher clinical value.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/41440
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	刘瑞雪. 基于液晶自适应光学的高对比度视网膜血管成像[D]. 中国科学院大学,2014.

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