Image Distortion of Optical Coherence Tomography

A kind of image distortion in Optical Coherence Tomography (OCT) resulted from average refractive index changes between structures of bio tissue is discussed for the first time.Analysis is given on following situations:1) Exact refraction index changes between microstructures;2)The gradient of average refractive index change between different tissue layers is parallel to the probe beam;3) The gradient of average refractive index change is vertical to the probe beam.The results show that the image distortion of situation 1) is usually negligible;in situation 2) there is a spread or shrink effect without relative location error; however,in situation 3) there is a significant image error inducing relative location displacement between different structures.Preliminary design to eliminate the distortion is presented,the method of which mainly based on the image classification and pixel array re arrangement.

APPLICATION OF DOPPLER OPTICAL COHERENCE TOMOGRAPHY IN RHEOLOGICAL STUDIES:BLOOD FLOW AND VESSELS MECHANICAL PROPERTIES EVALUATION

Doppler Optical Coherence Tomography(DOCT)is a noninvasive optical diagnostic technique,which is well suited for the quantitative mapping of microflow velocity profiles and the analysis of flow-vessel interactions.The noninvasive imaging and quantitative analysis of blood flow in the complex-structured vascular bed is required in many biomedical applications,including those where the determination of mechanical properties of vessels or the knowledge of the mechanic interactions between the flow and the housing medium plays a key role.The change of microvessel wall elasticity could be a potential indicator of cardiovascular disease at the very early stage,whilst monitoring the blood flow dynamics and associated temporal and spatial variations in vessel’s wall shear stress could help predicting the possible rupture of atherosclerotic plaques.The results of feasibility studies of application of DOCT for the evaluation of mechanical properties of elastic vessel model are presented.The technique has also been applied for imaging of sub-cranial rat blood flow in vivo.

AB077. Optical coherence tomography angiography

Optical coherence tomography(OCT)angiography is a new non-invasive imaging modality which is providing clinicians with an alternative to traditional dye-based angiography.The images are obtained using the concept of motion contrast and provide a quicker safer way to image the retinal and choroidal circulation.Not only are there practical aspects to support its integration but new insights are being made into the path;hysiology of various retinal choroidal diseases due to its ability to provide a 3-dimensional view of the vasculature which can be segmented in many ways to focus in on the circulation of a given anatomic region of the retina.We are currently in the phase of integration of this new technology into our practices.

基于端到端深度神经网络和图搜索的OCT图像视网膜层边界分割方法

视网膜层边界的形态变化是眼部视网膜疾病出现的重要标志,光学相干断层扫描(optical coherence tomography,OCT)图像可以捕捉其细微变化,基于OCT图像的视网膜层边界分割能够辅助相关疾病的临床判断.在OCT图像中,由于视网膜层边界的形态变化多样,其中与边界相关的关键信息如上下文信息和显著性边界信息等对层边界的判断和分割至关重要.然而已有分割方法缺乏对以上信息的考虑,导致边界不完整和不连续.针对以上问题,提出一种“由粗到细”的基于端到端深度神经网络和图搜索(graph search,GS)的OCT图像视网膜层边界分割方法,避免了非端到端方法中普遍存在的“断层”现象.在粗分割阶段,提出一种端到端的深度神经网络—注意力全局残差网络(attention global residual network,AGR-Net),以更充分和有效的方式提取上述关键信息.具体地,首先设计一个全局特征模块(global feature module,GFM),通过从图像的4个方向扫描以捕获OCT图像的全局上下文信息;其次,进一步将通道注意力模块(channel attention module,CAM)与全局特征模块串行组合并嵌入到主干网络中,以实现视网膜层及其边界的上下文信息的显著性建模,有效解决OCT图像中由于视网膜层形变和信息提取不充分所导致的误分割问题.在细分割阶段,采用图搜索算法去除AGR-Net粗分割结果中的孤立区域或和孔洞等,保持边界的固定拓扑结构和连续平滑,以实现整体分割结果的进一步优化,为医学临床的诊断提供更完整的参考.最后,在两个公开数据集上从不同的角度对所提出的方法进行性能评估,并与最新方法进行比较.对比实验结果也表明所提方法在分割精度和稳定性方面均优于现有方法.

基于改进MobileNetV2神经网络的视网膜OCT图像多分类

光学相干断层成像(optical coherence tomography,OCT)是一种具有无接触、高分辨率等特点的新型眼科医学诊断方法,现在已经作为医生临床诊断眼科疾病的重要参考物,但人工分类疾病费时费力,视网膜病变的早期发现和临床诊断至关重要.为了解决该类问题,本文提出了一种基于改进MobileNetV2神经网络对视网膜OCT图像多分类识别方法.此方法利用特征融合技术处理图像并设计增加注意力机制改进网络模型,二者在极大程度上提高OCT图像的分类准确率.与原有算法相比,分类效果具有明显提升,本文模型的分类准确率、召回值、精确度、F1值分别达到98.3%、98.44%、98.94%、98.69%,已经超越人工分类的准确率.此类方法不仅在实际诊断中加快诊断流程、降低医生负担、提高诊断质量,同时也为眼科医疗研究提供新的方向.

Dynamic Analysis of Mental Sweating by the Time-Sequential Piled-Up En-Face OCT Images

In this paper, the dynamic analysis of mental sweating for sound stimulus of a few tens of eccrine sweat glands is performed by the time-sequential piled-up en-face optical coherence tomography (OCT) images with the frame spacing of 3.3 sec. In the experiment, the amount of excess sweat can be evaluated simultaneously for a few tens of sweat glands by piling up of all the en-face OCT images. Strong non-uniformity is observed in mental sweating where the amount of sweat in response to sound stimulus is different for each sweat gland. Furthermore, the amount of sweat is significantly increased in proportion to the strength of the stimulus.

基于结构相似约束生成对抗网络的视网膜OCT图像去噪算法

光学相干断层扫描(OCT)图像中存在的散斑噪声会掩盖视网膜重要的形态学细节,妨碍视网膜病变的观察和临床诊断。提出了一种基于结构相似约束生成对抗网络的视网膜OCT图像去噪算法,基于残差策略改进生成对抗网络模型结构,并融合结构相似性损失约束模型优化,实现散斑噪声抑制,同时增强对视网膜结构细节的保留。在杜克大学发布的SD-OCT公开数据集上的实验表明,所提算法的峰值信噪比和边缘保持指数分别为28.08和0.960,优于所对比的其他去噪方法,且适用于其他来自A2A SD-OCT研究的公开数据集。

Anisotropic Total Variation Regularization Based NAS-RIF Blind Restoration Method for OCT Image

Based on anisotropic total variation regularization(ATVR), a nonnegativity and support constraints recursive inverse filtering(NAS-RIF) blind restoration method is proposed to enhance the quality of optical coherence tomography(OCT) image. First, ATVR is introduced into the cost function of NAS-RIF to improve the noise robustness and retain the details in the image.Since the split Bregman iterative is used to optimize the ATVR based cost function, the ATVR based NAS-RIF blind restoration method is then constructed. Furthermore, combined with the geometric nonlinear diffusion filter and the Poisson-distribution-based minimum error thresholding, the ATVR based NAS-RIF blind restoration method is used to realize the blind OCT image restoration. The experimental results demonstrate that the ATVR based NAS-RIF blind restoration method can successfully retain the details in the OCT images. In addition, the signal-to-noise ratio of the blind restored OCT images can be improved, along with the noise robustness.

眼底病变OCT图像的轻量化识别算法

为了准确、方便地识别多类型眼底病变,提出光学相干断层扫描技术(OCT)图像的轻量化分类模型MB-CNN.降低卷积核的使用个数,调节每个阶段卷积块的使用比例,设计轻量化主干网络L-Resnet,通过加深网络深度增强对深层语义信息的提取.使用深度可分离卷积设计多尺度卷积块MultiBlock,利用MultiBloc深度挖掘病灶区域的特征,使用不同的卷积核提取不同尺寸病变的特征,提高网络对病变OCT图像的识别能力.构建特征融合模块FFM,融合浅层信息和深层信息,充分提取病变特征的纹理和语义信息,提高对小目标病变的识别能力.实验结果显示,MB-CNN在UCSD、 Duke和NEH3个数据集上的总体分类精度分别达到97.2%、 99.92%和94.37%,模型参数量明显降低,所提模型能够针对眼底的多种病变进行分类.

SDOCT IMAGE RECONSTRUCTION BY INTERFEROMETRIC SYNTHETIC APERTURE MICROSCOPY

Spectral domain optical coherence tomography(SDOCT)is a noninvasive,cross-sectional imaging technique that measures depth resolved reflectance of tissue by Fourier transforming the spectral interferogram with the scanning of the reference avoided.Interferometric synthetic aperture microscopy(ISAM)is an optical microscopy computed-imaging technique for measuring the optical properties of biological tissues,which can overcome the compromise between depth of focus and transverse resolution.This paper describes the principle of SDOCT and ISAM,which multiplexes raw acquisitions to provide quantitatively meaningful data with reliable spatially invariant resolution at all depths.A mathematical model for a coherent microscope with a planar scanning geometry and spectral detection was described.The two-dimensional fast Fourier transform(FFT)of spectral data in the transverse directions was calculated.Then the nonuniform ISAM resampling and filtering was implemented to yield the scattering potential within the scalar model.Inverse FFT was used to obtain the ISAM reconstruction.One scatterer,multiple scatterers,and noisy simulations were implemented by use of ISAM to catch spatially invariant resolution.ISAM images were compared to those obtained using standard optical coherence tomography(OCT)methods.The high quality of the results validates the rationality of the founded model and that diffraction limited resolution can be achieved outside the focal plane.

Line-field confocal optical coherence tomography for three-dimensional skin imaging

This paper reports on the latest advances in line-field confocal optical cohere nee tomography(LC-OCT),a recently invented imaging technology that now allows the generation of either horizontal(x×y)section images at an adjustable depth or vertical(x×z)section images at an adjustable lateral position,as well as thre dimensional images.For both two-dimensional imaging modes,images are acquired in real-time,with real-time control of the depth and lateral positions.Three-dimensional(x×y×z)images are acquired from a stack of horizontal section images.The device is in the form of a portable probe.The handle of the probe has a button and a scroll wheel allowing the user to control the imaging modes.Using a supercontinuum laser as a broadband light source and a high numerical microscope objective,an isotropic spatial resolution of^1|im is achieved.The field of view of the three-dimensional images is 1.2 mm×0.5 mm×0.5 mm(x×y×z).Images of skin tissues are presented to demonstrate the potential of the technology in dermatology.

小波变换对OCT图像的降噪处理

通过分析光学相干层析成像系统中的噪音源以及不同噪音对成像质量的影响,利用小波变换的方法,结合软阈值滤波对图像去噪,消除噪音对图像的干扰,处理后图像变得清晰了,图像质量得以改善,表明该方法能达到减小图像噪音的目的·

In-vivo retinal imaging by optical coherence tomography using an RSOD-based phase modulator

Fourier-domain rapid scanning optical delay line (RSOD) was introduced for phase modulation and depth scanning in a time-domain optical coherence tomography (TD-OCT) system. Investigation of parameter optimization of RSOD was conducted. Experiments for RSOD characterization at different parameters of the groove pitch, focal length, galvomirror size, etc. were performed. By implementing the optimized RSOD in our established TD-OCT system with a broadband light source centered at 840 nm with 50 nm bandwidth, in vivo retina imaging of a rabbit was presented, demonstrating the feasibility of high-quality TD-OCT imaging using an RSOD-based phase modulator.

应用多级维纳滤波的OCT图像除噪方法

设计了基于维纳滤波和对比度增强的OCT图像处理方法。对OCT图像的噪声进行了分析，通过多尺度维纳滤波器对图像进行滤波处理来去除噪声干扰，然后根据区域特性采用对比度增强方法提高图像对比度。实验结果表明：经该方法处理后图像的背景方差（BV）较原始图像降低了2～6倍，细节方差和背景方差之比（DV／BV）提高了2～5倍。该方法不仅有效地去除了OCT图像的噪声，而且视觉效果良好，是一种有效的图像后处理方法。

基于旋转扫描探头的OCT内窥成像系统设计

为了同时获取样品的表面和深度信息,研究光学相干层析的成像原理,建立了基于光学相干层析技术的内窥系统,实现了旋转扫描成像,系统的工作波长为1310nm,工作带宽为80nm.理论推导及计算机仿真得到了系统信噪比与干涉仪的分光比、反射率之间的关系并分析了理论分辨率和探测深度.提出外径为5mm的内窥镜扫描探头,聚焦距离为12mm,数值孔径NA为0.47,折射率分布常量A=0.2187.利用微型电机驱动直角棱镜实现扫描,旋转速度为25rpm,旋转一周得到640个采样点.采用多层盖玻片和洋葱表皮作为样品进行实验分析,得到了盖玻片和洋葱的图像,横向分辨率和纵向分辨率分别为10μm和15μm.结果表明,设计的光学相干层析内窥系统能够用于旋转扫描成像,获取更多的组织信息.

利用Monte Carlo模拟技术研究OCT图像对比度

建立了光在生物组织中传播的模型,利用MonteCarlo模拟技术快速计算和可移植性的优点,研究了OCT图像对比度与显微物镜数值孔径、焦距深度、时间门参数的关系,并给出它们的关系曲线。通过在所建立的模型基础上加入透镜透过率函数和光学传递函数,弥补了以往程序只能模拟光在生物组织中传播行为的缺点。该模型不仅可以分析生物组织图像与生物光学特性的关系,而且还可以指导OCT结构的完善和创新。模拟结果表明:在构建OCT时,参考臂与样品臂的这两个显微物镜的数值孔径越大,生物组织的采样深度越浅,处理信号的时间门宽度越小(但时间门宽度不能小于激光脉冲时间),混浊生物组织图像对比度越好。

基于波原子阈值算法的OCT图像降噪技术

为了消除或缓解光学相干断层成像方法中散斑等噪声对OCT图像像质退化的影响,提出了基于波原子阈值去噪算法。波原子变换是一种新型的二维多尺度变换,且满足曲线波的抛物比例尺度关系和各向异性征;波原子适用于模式的任意局部方向,能够对轴方向的各向异性模式稀疏展开。本文利用波原子阈值去噪算法,对人眼眼底组织和手指指尖皮肤的OCT图像进行降噪处理,并与传统的小波阈值算法和快速曲波算法对OCT样品图像去噪效果进行对比分析。结果表明,基于波原子阈值去噪方法能够有效地抑制OCT图像散斑噪声,并能保持图像边缘细节特征。

复谱频域OCT成像的研究

采用频域技术的OCT系统,深度扫描信息由背向散射光谱的傅立叶反变换获得,简化了轴向扫描过程,从而使快速OCT成像成为可能.为了实现复杂生物组织的OCT快速成像,消除谱频域OCT的"混叠"现象、重建样品的真实层析结构,本文引入了相移干涉技术,构建了一套满量程复谱频域OCT实验系统,并为系统设计了特殊的分束镜和移相器,为最终实现复杂生物组织的OCT快速成像提供了条件.

基于一种新小波变换的OCT图像去噪方法

散斑在OCT图像中既是信息载体,也是一种严重的噪声。针对OCT图像的这一特点,提出一种基于小波变换和维纳滤波相结合的OCT图像去噪方法。通过对OCT图像进行小波分解,得到四个不同频带的子图像,保持低频部分不变,对另外三个高频细节图像进行维纳滤波,将低频子图像和三个滤波后的高频细节子图像进行小波反变换,得到去噪后的图像。实验结果表明小波变换和维纳滤波相结合的方法对OCT图像有比较理想的去噪效果。

EDISD-OCT的眼科应用

频域相干光断层深度增强成像(EDI SD-OCT)是在频域相干光断层成像技术(SD-OCT)的基础上通过深度增强成像,可以清楚的观察脉络膜组织形态的变化及对脉络膜厚度进行测量。目前,对EDI SD-OCT的应用主要是在测量脉络膜厚度上,这样,对许多波及脉络膜的眼部疾病有辅助诊断作用,如:高度近视眼、年龄相关性黄斑变性、青光眼、中心性浆液性脉络膜视网膜病变、各种脉络膜肿瘤等;此外对多种疾病的鉴别诊断和疗效的随诊观察有很大的应用价值。