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。     

Speckle reduction by I-divergence regularization in optical coherence tomography

For optical coherence tomography (OCT), ultrasound, synthetic-aperture radar, and other coherent ranging methods, speckle can cause spurious detail that detracts from the utility of the image. It is a problem inherent to imaging densely scattering objects with limited bandwidth. Using a method of regularization by minimizing Csiszar's I-divergence measure, we derive a method of speckle minimization that produces an image that both is consistent with the known data and extrapolates additional detail based on constraints on the magnitude of the image. This method is demonstrated on a test image and on an OCT image of a Xenopus laevis tadpole.     

基于CCD探测器的全视场层析成像方法研究

由正弦信号驱动PZT调制参考镜以实现参考光相位调制,CCD光探测器的曝光时间为正弦驱动信号的四分之一周期,利用频率-同步探测技术,在一个参考光调制周期共提取四帧全视场参考光与样品反射和散射光干涉图像.为了获得最优的参考光信号调制参数,一种基于PID控制器的闭环控制技术与数字移相相结合的方法用于调制系统,采用50Hz的理想正弦曲线的数字离散量来控制PZT的调制幅度,数字移相电路调整PZT的振动相位来保证最优调制参数的获得.CCD(频率f=200Hz)由软件驱动,采用积分算法,实现了由CCD探测器提取微弱全视场层析信号的方法.     

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。     

Speckle reduction in optical coherence tomography images using digital filtering

Speckle noise is a ubiquitous artifact that limits the interpretation of optical coherence tomography images. Here we apply various speckle-reduction digital filters to optical coherence tomography images and compare their performance. Our results indicate that shift-invariant, nonorthogonal wavelet-transform-based filters together with enhanced Lee and adaptive Wiener filters can significantly reduce speckle and increase the signal-to-noise ratio, while preserving strong edges. The speckle reduction capabilities of these filters are also compared with speckle reduction from incoherent angular compounding. Our results suggest that by using these digital filters, the number of individual angles required to attain a certain level of speckle reduction can be decreased.     

Polypyrrole nanoparticles: a potential optical coherence tomography contrast agent for cancer imaging

A near-infrared (NIR) absorbing contrast agent based on polypyrrole nanoparticles is described. Quantitative optical coherence tomography studies on tissue phantoms and Mie scattering calculations indicate their potential application for early-stage cancer diagnosis.     

Enhancement of intrinsic optical signal recording with split spectrum optical coherence tomography

Functional optical coherence tomography (OCT) of stimulus-evoked intrinsic optical signal (IOS) promises to be a new methodology for high-resolution mapping of retinal neural dysfunctions. However, its practical applications for non-invasive examination of retinal function have been hindered by the low signal-to-noise ratio (SNR) and small magnitude of IOSs. Split spectrum amplitude-decorrelation has been demonstrated to improve the image quality of OCT angiography. In this study, we exploited split spectrum strategy to improve the sensitivity of IOS recording. The full OCT spectrum was split into multiple spectral bands and IOSs from each sub-band were calculated separately and then combined to generate a single IOS image sequence. The algorithm was tested on in vivo images of frog retinas. It significantly improved both IOS magnitude and SNR, which are essential for practical applications of functional IOS imaging.     

SS-OCTA对黑色素瘤皮肤结构和血管的成像实验

扫频源光学相干层析血管成像(SS-OCTA)是一种基于分频幅去相关血管造影法(SSADA)的新型血管成像技术,在肿瘤等疾病的早期诊断方面拥有较大前景。本文在5.12 mm×5.12 mm成像视场、标准图像最大信噪比34.3dB的SS-OCTA成像平台,对黑色素瘤C57BL6小鼠进行皮肤结构和血管成像采集。结果表明在皮肤科疾病的早期诊断方面,利用SS-OCTA系统进行血管成像优于结构成像。     

A lightweight deep learning model for retinal optical coherence tomography image classification

Automated retinal disease detection and grading is one of the most researched areas in medical image analysis. In recent years, Deep Learning models have attracted much attention in this field. Hence, in this paper, we present a Deep Learning-based, lightweight, fully automated end-to-end diagnostic system for the detection of the two major retinal diseases, namely diabetic macular oedema (DME) and drusen macular degeneration (DMD). Early detection of these diseases is important to prevent vision impairment. Optical coherence tomography (OCT) is the main imaging technique for detecting these diseases. The model proposed in this work is based on residual blocks and channel attention modules. The performance of the model is evaluated using the publicly available Mendeley OCT dataset and the Duke dataset. We were able to achieve a classification accuracy of 99.5% in the Mendeley test dataset and 94.9% in the Duke dataset with the proposed model. For the application, we performed an extensive evaluation of pre-trained models (LeNet, AlexNet, VGG-16, ResNet50 and SE-ResNet). The proposed model has a much smaller number of trainable parameters and shows superior performance compared to existing methods.     

基于字典算法的OCT图像散斑稀疏降噪

光学相干层析扫描(OCT)作为一种新型无创高分辨率扫描方式,在临床上得到广泛应用,但是OCT图像本身存在严重的散斑噪声,这大大影响了疾病的诊断。本文针对OCT图像中的乘性散斑噪声,改进了两种原始字典降噪算法。该算法首先对OCT图像进行对数变换,采用正交匹配追踪算法进行稀疏编码,以及K奇异值分解学习算法进行自适应字典的更新,最后通过加权平均以及指数变换回到空域。实验结果表明,本文改进的两种字典算法能有效降低OCT图像中的散斑噪声,获得良好的视觉效果。并通过均方误差(MSE)、峰值信噪比(PSNR)、结构相似性(SSIM)以及边缘保持指数(EPI)四个指标评价降噪效果,与两种原始字典降噪算法和传统滤波算法相比,两种改进字典算法降噪效果优于其他算法,其中自适应字典算法表现更好。     

Coupling efficiency of optical coherence tomography system with gradient refractive index rod lens as reference arm

The coupling efficiency equation of an optical coherence tomography system with a gradient refractive index rod lens as the reference arm is established and discussed theoretically and experimentally. The experimental result is consistent with the theoretical result. The higher coupling efficiency of the OCT system can be obtained if θ, which is the angle between the mirror and the y axis, is smaller than 0.5°.     

Reduction of speckle noise from optical coherence tomography images using multi-frame weighted nuclear norm minimization method

In this paper, we propose a speckle noise reduction method for spectral-domain optical coherence tomography (SD-OCT) images called multi-frame weighted nuclear norm minimization (MWNNM). This method is a direct extension of weighted nuclear norm minimization (WNNM) in the multi-frame framework since an adequately denoised image could not be achieved with single-frame denoising methods. The MWNNM method exploits multiple B-scans collected from a small area of a SD-OCT volumetric image, and then denoises and averages them together to obtain a high signal-to-noise ratio B-scan. The results show that the image quality metrics obtained by denoising and averaging only five nearby B-scans with MWNNM method is considerably better than those of the average image obtained by registering and averaging 40 azimuthally repeated B-scans.     

Determining elastic properties of skin by measuring surface waves from an impulse mechanical stimulus using phase-sensitive optical coherence tomography

The mechanical properties of skin are important tissue parameters that are useful for understanding skin patho-physiology, which can aid disease diagnosis and treatment. This paper presents an innovative method that employs phase-sensitive spectral-domain optical coherence tomography (PhS-OCT) to characterize the biomechanical properties of skin by measuring surface waves induced by short impulses from a home-made shaker. Experiments are carried out on single and double-layer agar–agar phantoms, of different concentrations and thickness, and on in vivo human skin, at the forearm and the palm. For each experiment, the surface wave phase-velocity dispersion curves were calculated, from which the elasticity of each layer of the sample was determined. It is demonstrated that the experimental results agree well with previous work. This study provides a novel combination of PhS-OCT technology with a simple and an inexpensive mechanical impulse surface wave stimulation that can be used to non-invasively evaluate the mechanical properties of skin in vivo, and may offer potential use in clinical situations.     

A novel optical coherence tomography-based micro-indentation technique for mechanical characterization of hydrogels.

Depth-sensing micro-indentation has been well recognized as a powerful tool for characterizing mechanical properties of solid materials due to its non-destructive approach. Based on the depth-sensing principle, we have developed a new indentation method combined with a high-resolution imaging technique, optical coherence tomography, which can accurately measure the deformation of hydrogels under a spherical indenter at constant force. The Hertz contact theory has been applied for quantitatively correlating the indentation force and the deformation with the mechanical properties of the materials. Young's moduli of hydrogels estimated by the new method are comparable with those measured by conventional depth-sensing micro-indentation. The advantages of this new method include its capability to characterize mechanical properties of bulk soft materials and amenability to perform creeping tests. More importantly, the measurement can be performed under sterile conditions allowing non-destructive, in situ and real-time investigations on the changes in mechanical properties of soft materials (e.g. hydrogel). This unique character can be applied for various biomechanical investigations such as monitoring reconstruction of engineered tissues.     

Evaluation of art subjects implemented in the marquetry technique by the optical coherence microscopy method

Evaluation of internal microstructure of decorative and applied art objects implemented in the intarsia and marquetry techniques by the optical coherence tomography method is considered. The high resolving optical coherence microscope with a radiation source with tunable wavelength in the range of 1305 ± 75 nm was applied. The ability to analyse layered microstructure of wood object surface layer in intarsia regions is demonstrated. The geometric features evaluation of the object's microstructure in the areas of interest was conducted. Systematisation of layers structure and typical defects inherent in intarsia regions was performed considering the structural features that may be important for restoration of such objects. Examples of experimentally obtained B‐scans and three‐dimensional representations of sample fragments of microstructure studied by the optical coherence microscopy method are given.     

基于数字希尔伯特变换的OCT信号处理与系统实现

信号处理方法的选择是光学相干层析(OpticalCoherenceTomography,OCT)系统研制的重要环节,直接决定着OCT系统的硬件构建和实现。应用硬件实现OCT信号处理的方法虽然速度快,但存在硬件开销大,系统配置可调节性差等缺点。进而采用了基于数字希尔伯特变换的软件方法来处理OCT信号。该数字处理方法对探测得到的离散干涉实信号进行解析拓展,得到同时具有振幅信息和相位信息的复信号,其中的振幅信息被用于OCT的图像重建。介绍了研制的光纤OCT系统和各驱动单元的同步时序控制,最后给出了人体皮肤和洋葱的OCT高清晰层析图。     

光学相干层析成像三维分辨率测试模拟眼

尽管OCT早已在世界范围内获得临床诊断许可,但这项技术尚无任何国际标准。如何验证OCT的成像能力及有效性被认为是该技术标准化进程中的重要一环。本研究研制了一种可用于OCT三维成像分辨率测试的模拟眼。该模拟眼利用透明树脂材料仿真了人眼的重要光学元件:角膜与晶状体。采用3D打印技术在模拟眼眼底制作出了参照USAF1951靶板设计的三维分辨率测试图案。研究结果表明该模拟眼能够对OCT设备的三维成像分辨率性能进行初步评估,通过进一步改进,未来可用于注册检验或日常质控。     

Discontinuous Galerkin method for the forward modelling in optical diffusion tomography

We propose a discontinuous Galerkin discretization scheme for the forward modelling in optical diffusion tomography in highly scattering media to facilitate dynamic mesh adaptation for complex domains. In addition, the numerical method is also shown to effectively deal with inhomogeneities in optical properties and refractive index mismatch at material interfaces. The accuracy of the method is demonstrated over a model concentric spherical layers problem where the discontinuous Galerkin method is compared against an analytical solution. Copyright © 2010 John Wiley & Sons, Ltd.     

Completely passive method of speckle reduction utilizing static multimode optical fibre and two-dimensional diffractive optical element

ABSTRACT

In this paper, we present experimental results on speckle noise suppression using a completely passive method. The passivity of the method is achieved owing to the absence of any mechanical, electronic, or other dynamic influences on the optical scheme elements. In the experiment, a multimode semiconductor 520?±?5-nm laser with a spectral bandwidth of 2?nm, static two-dimensional (2D) and 2?×?1D diffractive optical elements (DOEs), as well as multimode single-core optical fibre and multimode optical fibre bundle were used. The dependence of the speckle reduction efficiency as a function of the optical fibre type and optical fibre length was measured for different DOEs. A speckle contrast of 0.148 and speckle reduction coefficient of 2.38 were obtained for a 2.5-m-long multimode optical fibre bundle. The experimental results confirmed that it is possible to construct completely passive optical circuits with reduced speckle noises using static multimode optical fibres and diffraction optical elements.