眼科光学相干断层(OCT)成像设备的计量研究

正光学相干层析(Optical Coherence Tomography,OCT)成像是一种新型三维断层成像技术,已经成为眼科无损成像的研究热点,相应的商业化进程也迅速展开。一、眼科OCT国际与国内标准研究现状根据美国Markets and Markets调研机构报告显示,2012年全世界OCT设备市场份额达到了8亿美元,而且预期至2018年其市场规模将增至10亿美元。与之形成鲜明对比的是,关于OCT技术的各项标准严重匮乏,不论是国际标准还是国内标准都尚未发布,极大     

快速高分辨率的频谱光学相干层析成像系统研究

光学相干层析成像（OCT）是一种用于生物组织成像的新型技术.该技术在非接触及无创成像方面的分辨率可达到微米量级.目前,大多数的OCT系统主要为时域OCT,为获取深度图像,需要对参考臂的光程进行长度扫描,采集速度受到了限制.为此研制了一套频谱OCT系统,由于该系统避免了参考扫描,故可实现极高的采集速度（1 000线/s）,使实时成像成为可能;分析了频谱OCT的理论探测深度（6.26 mm）和分辨率（13μm）;应用该系统对50μm厚的塑料薄膜进行了成像,实验证明实际分辨率高于50 μm.     

采用频域快速延迟线的光学相干层析系统的研制

建立了一套单模光纤型光学相干层析(OCT)成像系统。系统采用了不同于国内其他组的新型频域快速扫描延迟线(FD-ODL)和外差平衡接受技术,采取了一系列提高系统信噪比的方法,成功地实现高信噪比(113dB)、高分辨率、大成像深度的层析图像的提取,获得了纵向分辨率9μm、横向分辨率10μm、深度2.88μm的清晰的皮肤OCT图像。该系统比传统的采用时域延迟线的OCT在信噪比上高出了一个量级。     

无损检测新工具——扫描激光声学显微镜

许多年来,超声检验已广泛用作无损检验的一个手段。对于大多数大型结构,由于受有限的频率范围(1～10MHz)限制,无法检测宏观缺陷。 随着材料技术的进展,需要研制高分辨率的无损检测设备。近年来,扫描激光声学显微镜研制成功,并开始进入实用阶段。扫描激光声学显微镜(SLAM)是一种高频超声映象装置,它可以使在光学上不透明材料的内部产生放大的图象。它具有10～500MHz的广阔的频率范围,能够检验大型零件的内部缺陷,也可以用于小型零件的探测。由于高频范围,使显微镜结构探测进入微观范围。高频能力可使扫描激光声学     

基于OCT成像的淡水无核珍珠内部缺陷自动检测方法

光学相干层析技术(OCT)作为一种高分辨率的无损光学检测手段,已被用于珍珠的内部质量检测。针对淡水无核珍珠质层内部缺陷检测的需求,提出一种通过光学相干层析图像实现淡水无核珍珠内部缺陷自动检测的方法。根据珠层灰度变化的特点,识别图像中缺陷区域的梯度特征和缺陷位置变化特征,并利用缺陷特征建立反向传播神经网络模型。实验中采集了内部无缺陷和内部有多种类型缺陷淡水无核珍珠的光学相干层析图像各20幅,对图像进行预处理并提取特征,利用K-means算法检测样本类型与所提取特征的匹配度,用特征与类型相匹配的样本特征训练反向传播神经网络模型,使用反向传播网络模型对淡水无核珍珠内部缺陷层进行分类识别。实验结果表明该方法提取特征的匹配度为92.5%,分类准确率达到100%,验证了该方法的可行性和有效性,提出的方法能够作为淡水无核珍珠内部缺陷识别和自动分类的有效手段。     

光学相干层析技术在眼科手术导航方面的研究进展

在眼科显微手术中,传统的术中成像方式由于缺少深度信息,限制了内部结构和手术器械的可视化。光学相干层析成像技术(OCT)是一种非接触式断层成像技术,由于其能提供深度信息、非侵入、成像快、分辨率高等优点,被广泛应用于眼科手术的术中导航。典型的OCT设备可分为手持OCT和显微镜集成OCT。本文简要介绍了时域OCT和频域OCT的原理和发展,回顾了OCT眼科手术导航设备的发展历程,并对各个类别中有代表性的OCT系统进行了介绍,对其成像原理、性能、优缺点等进行了描述和对比,最后对该技术在眼科手术中的应用做出了总结和展望。     

线聚焦光学相干层析术的研究

提出了一种高速光学相干层析(OCT)成像技术方案。利用柱面镜的成像特性将传统OCT的点聚焦成像模式改变为线聚焦成像模式,从而降低二维OCT图像的扫描维数,达到提高成像速度的目的。利用ZEMAX光学软件对系统进行光线追迹获得光束经过柱面镜后的聚焦情况。随后采用635nm的激光光源和柱面镜构建了实验系统,实验结果很好地验证了光线追迹仿真结果。     

基于共聚焦的基因生物成像系统设计

针对常规基因生物成像系统无法满足快速高分辨率基因成像需求等实际问题,该文设计了一种基于共聚焦的基因生物成像系统。根据基因生物成像的基本原理设计一种基于共聚焦结构、采用落射照明方式的实时荧光生物成像光学结构,通过仿真分析确定光学结构,优化系统参数,采用2路激光作为激发光源搭建试验验测试装置。结果表明,该文设计的基因生物成像系统的分辨率小于或等于10μm/px,最低检出限小于10个荧光分子/μm²,样本检测重复性小于或等于10%,与传统的生物成像系统相比,该系统提高了扫描效率且保证了高分辨率成像,同时更好地实现了光学系统均匀照明的功能。     

切变照相—一种实用的无损检验新方法

切变照相(Shearography)是在原先为应变测量而研制的图象—切变照相机的基础上发展起来的一种新型无损检验技术。1982年,美国Oakland大学Y·Y·Hung研究了一种应变测量的新的光学方法,即激光光学方法。随后改进成为切变照相技术。它等同于全场应变测量仪,可以在大面积上观测应变,从而揭示表面裂纹和内部裂纹。     

光纤型偏振OCT系统中光偏振特性的研究

建立了偏振光在生物组织中传播的模型,并利用该模型模拟了偏振光在生物组织中传播的过程,重建了多种偏振态输入光的情况下光偏振态在生物组织中的分布及生物组织的偏振特性模型.分析了光偏振度与光被生物组织散射次数的关系,阐明了由于偏振光在组织中传播,其偏振态逐渐改变而造成的偏振OCT 干涉计两臂光束失去相干性及偏振OCT 图像质量下降现象.通过分析斯托克斯(Stokes)矢量和穆勒(Muller)矩阵在光纤型偏振OCT系统中的应用,说明Muller 矩阵不受输入光偏振态的影响,因此它比Stokes 矢量更适用于光纤型偏振OCT 系统研究.     

Unbalanced versus balanced operation in an optical coherence tomography system

The choice of a balanced optical coherence tomography (OCT) configuration versus an unbalanced OCT configuration with optimized reference-arm attenuation is discussed. The choice depends on the receiver noise, the fiber-end reflection R, and the power to the object. When OCT is used to investigate biological tissue an equivalent R? can be evaluated as the compound reflected light from tissue. In this case an additional parameter has to be considered: the confocal optical sectioning interval of the OCT system.     

Dispersion in a grating-based optical delay line for optical coherence tomography

Optical coherence tomography (OCT) is a high-resolution imaging technology based on low-coherence interferometry. When OCT imaging is performed in biological tissue, dispersion almost inevitably occurs. We quantify the group-velocity dispersion that a grating-based optical delay line may induce and its contribution to the axial point-spread function of OCT. Among the practical reasons for modeling the dispersion in grating-based optical delay line is that, at maximum compensation, it can provide insight into the dispersive properties of tissues.     

Depth-resolved two-dimensional stokes vectors of backscattered light and mueller matrices of biological tissue measured with optical coherence tomography

Mueller matrices provide a complete characterization of the optical polarization properties of biological tissue. A polarization-sensitive optical coherence tomography (OCT) system was built and used to investigate the optical polarization properties of biological tissues and other turbid media. The apparent degree of polarization (DOP) of the backscattered light was measured with both liquid and solid scattering samples. The DOP maintains the value of unity within the detectable depth for the solid sample, whereas the DOP decreases with the optical depth for the liquid sample. Two-dimensional depth-resolved images of both the Stokes vectors of the backscattered light and the full Mueller matrices of biological tissue were measured with this system. These polarization measurements revealed some tissue structures that are not perceptible with standard OCT.     

Lensed fiber probes designed as an alternative to bulk probes in optical coherence tomography

We demonstrate a compact all-fiber sampling probe for an optical coherence tomography (OCT) system. By forming a focusing lens directly on the tip of an optical fiber, a compact sampling probe could be implemented. To simultaneously achieve a sufficiently long working distance and a good lateral resolution, we employed a large-mode area photonic crystal fiber (PCF) and a coreless silica fiber (CSF) of the same diameters. A working distance of up to 1270 microm, a 3 dB distance range of 2210 microm, and a transverse resolution of 14.2 microm were achieved with the implemented PCF lensed fiber; these values are comparable to those obtainable with a conventional objective lens having an NA of 0.25 (10 x). The performance of the OCT system equipped with the proposed PCF lensed fiber is presented by showing the OCT images of a rat finger as a biological sample and a pearl as an in-depth sample.     

复谱频域OCT系统高分辨率图像重建

为了提高复杂多层样品层析图像的分辨率,构建了复谱频域光学相干层析成像(CSOCT)系统.由于其在低亮度和高速成像方面相对于时域OCT具有更高的灵敏度,因此在光学相干层析成像系统中具有重要的作用.本文对测试样品二层盖波片进行成像实验,基于光学相干层析基本理论,采用五帧相移算法,最终获得测试样品的复谱频域OCT图像.实验结果表明,该系统可以消除谱频域OCT图像中的寄生项和镜像,改善和提高层析图像的分辨率.     

Dispersion compensation in high-speed optical coherence tomography by acousto-optic modulation

We report studies of the analyses of and compensation for group dispersion to improve the axial resolution of high-speed optical coherence tomography (OCT) by acousto-optic modulation (AOM). Theoretical modeling and experiments reveal that the high-order group dispersion induced by acousto-optic crystals broadens the measured coherence length (Lc) and thus degrades the axial resolution of OCT imaging. Based on our experimental studies, we can compensate for the dispersion to less than 50% broadening of the source Lc by adjusting the grating-lens-based optical delay in the reference arm and can further eliminate it by inserting like acousto-optic crystals in the sample arm of the OCT system. The results demonstrate that this AOM-mediated OCT system permits high-performance OCT imaging at A-scan rates of as much as 4 kHz by use of a resonant scanner. Because of its ultrastable direct frequency modulation, this AOM-mediated OCT system can potentially improve the performance of high-speed Doppler OCT techniques.     

Optimization of dual-band continuum light source for ultrahigh-resolution optical coherence tomography

We demonstrate a dual-band continuum light source centered at 830 and 1300 nm for optical coherence tomography (OCT) generated by pumping a photonic crystal fiber having two closely spaced zero-dispersion wavelengths with a femtosecond laser at 1059 nm. By use of polarization control, sidelobe suppression can be improved up to approximately 7.7 dB. By employing compression of the pump pulses, the generated spectrum is smooth and near-Gaussian, resulting in a point-spread function with negligible sidelobes. We demonstrate ultrahigh-resolution OCT imaging of biological tissue in vivo and in vitro using this light source and compare it with conventional-resolution OCT imaging at 1300 nm.     

Theoretical model of optical coherence tomography for system optimization and characterization

We present a detailed analytical model to describe optical coherence tomography (OCT) systems, which considers the propagation of the optical field within a scattering medium in the framework of the extended Huygens-Fresnel principle. The model includes use of the discrete-particle model and the fractal approach in treating biological tissue as being packed with scattering particles with a power-law distribution. In contrast to previous models, an imaginary lens proximal to the tissue surface is introduced that approximates the real focusing lens in the sample arm of the OCT system. This treatment avoids the consideration of backscattering light as traveling in the free space between the focusing lens and the tissue surface before mixing with the reference beam. Experiments on tissue phantoms were carried out to verify the validity of this model.     

Speckle properties of the logarithmically transformed signal in optical coherence tomography

We discuss the statistical properties of speckle of the logarithmically transformed signal in optical coherence tomography (OCT) both theoretically and experimentally. OCT signals of Intralipid solution with different volume particle concentrations ρ (correspondingly, scattering coefficient μ(s) ranges from 1.25 to 25.11 mm(-1)) were measured and analyzed under two different focusing conditions [numerical apertures (NAs) of the objective lens of 0.13 and 0.25]. We found that the effect of the speckle noise can be suppressed by displaying OCT images in the logarithmic scale and by using the objective lens with a higher NA. We also found that the speckle properties are correlated with the scattering properties of the sample, which may be used to characterize the scattering properties of biological tissue. The simulated OCT image and the in vitro OCT image of a rat liver are used as examples to demonstrate the feasibility of the method.     

Wide-Field Three-Dimensional Depth-Invariant Cellular-Resolution Imaging of the Human Retina

Three-dimensional (3D) cellular-resolution imaging of the living human retina over a large field of view will bring a great impact in clinical ophthalmology, potentially finding new biomarkers for early diagnosis and improving the pathophysiological understanding of ocular diseases. While hardware-based and computational adaptive optics (AO) optical coherence tomography (OCT) have been developed to achieve cellular-resolution retinal imaging, these approaches support limited 3D imaging fields, and their high cost and intrinsic hardware complexity limit their practical utility. Here, this work demonstrates 3D depth-invariant cellular-resolution imaging of the living human retina over a 3 × 3 mm field of view using the first intrinsically phase-stable multi-MHz retinal swept-source OCT and novel computational defocus and aberration correction methods. Single-acquisition imaging of photoreceptor cells, retinal nerve fiber layer, and retinal capillaries is presented across unprecedented imaging fields. By providing wide-field 3D cellular-resolution imaging in the human retina using a standard point-scan architecture routinely used in the clinic, this platform proposes a strategy for expanded utilization of high-resolution retinal imaging in both research and clinical settings.