时域光学相干层析系统噪音分析和实验研究

本文从理论和实验上分析了存在拍频噪音时时域光学相干层析系统的噪音特性,给出了拍频噪音的具体估算方法.建立了描述一般时域光学相干层析系统实际噪音的简化模型,并给出了测量和寻找平衡探测光学相干层析系统最佳工作状态的方法.理论计算表明,平衡探测光学相干层析系统的信噪比受限于拍频噪音,理想情况下,最大信噪比可达100 dB左右|同时实验表明,如果实际的系统不能完全消除冗余噪音,其信噪比可能要比理论值小10~20 dB.本文的主要结果将可直接用于时域光学相干层析系统工作状态的测试和诊断当中,对频域光学相干层析系统噪音性能的分析和优化也将有所裨益.     

Performance analysis of a swept-source optical coherence tomography system with a quadrature interferometer and optical amplification

A performance analysis of signal to noise ratio for an optical coherence tomography system with quadrature detection and a semiconductor optical amplifier in the sample arm is discussed. The results are compared and discussed in relation to a conventional OCT system (without optical amplification). An increase of the signal to noise ratio up to 14 dB at a depth of 0.5 mm is obtained compared to the system without the optical amplifier. Overall, an improvement was demonstrated for signal coming from deeper regions within the samples. Arterial plaque from a myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbit is visualized and characterized using this system. Improvement of signal to noise ratio increases the penetration depth possible for OCT images, from 1 mm to 2 mm within the vessel wall of an artery. Preliminary results show that vulnerable plaque with fibrous cap, macrophage accumulations and calcification in the arterial tissue are measurable with this OCT system.     

Speckle reduction in optical coherence tomography images by use of a spatially adaptive wavelet filter

A spatially adaptive two-dimensional wavelet filter is used to reduce speckle noise in time-domain and Fourier-domain optical coherence tomography (OCT) images. Edges can be separated from discontinuities that are due to noise, and noise power can be attenuated in the wavelet domain without significantly compromising image sharpness. A single parameter controls the degree of noise reduction. When this filter is applied to ophthalmic OCT images, signal-to-noise ratio improvements of >7 dB are attained, with a sharpness reduction of <3%.     

Simulation of basic characteristics of single-shot full-field optical coherence tomography using spatially phase-modulated reference light

For the single-shot full-field optical coherence tomography (OCT) using spatially phase-modulated reference light, the basic characteristics have been simulated. At low spatial frequencies, the OCT signal intensity is enhanced twofold owing to subtractions, and with increasing the spatial frequency, the OCT signal intensity decreases 0.636 times at half the Nyquist frequency. OCT signal intensities also depend on orientations in images. Residual noninterference components of signal intensities between adjacent uniform areas increase background noise and reduce the system sensitivity. In the reference light, the optimum phase difference between adjacent uniform areas is 180 deg. Deviations from 180 deg reduce subtracted interference components. It is important that interference intensity, noninterference components and phases between adjacent uniform areas be approximately the same to obtain the OCT image with the reduction of background noise stably.     

Fiber type of optical coherence tomography with an auto-focus device

Optical coherence tomography (OCT) is a novel technique for non-invasive imaging based on low coherence interferometer. In this study, we develop a new optical fiber type of OCT with a commercial auto-focus device to simultaneously measure the refractive index and thickness of a single-layer for demonstration. An auto-focus device can be easily implemented into the new OCT in order to diminish the measurement error resulting from the slight vibration of the sample and/or the sample stage. However, if the conventional OCT is implemented with an auto-focus device, it would be extremely difficult in locating and controlling the positions of the sample and scanning stages.From the experimental results, the error percentage from various frequency of the simulated noise is almost under 0.4%. Due to the resonance frequency of a DVD pickup head is around 40 Hz, the error percentage is apparently highest up to 1%; however still acceptable. It is concluded that the auto-focus device indeed works in an OCT system.     

结合计算层析与光学相干层析测量折射率分布

通过将计算层析技术与光学相干层析技术相结合,测量散射介质非均匀折射率分布。该方法测量散射样品折射率分布时,通过光学相干层析技术测量散射样品折射率分布在多个方向上的投影,采用计算层析技术实现对样品折射率分布的层析重建,克服了传统折射率光学测量方法如单纯的基于光学相干层析原理的焦点追迹法和光程匹配法,不能测量散射介质非均匀折射率分布的缺点。采用该方法在实验中对梯度折射率棒的径向相对折射率分布进行层析重建,取得了较好的实验结果。     

Optical Coherence Tomography Premiere in Korea

Optical Coherence Tomography (OCT) is considered as fundamentally new image modality having advantages such as high-speed, real-time cross sectional imaging with non-invasive in vivo investigation of biological tissue and its potential for clinical application is highly evaluated. In spite of these merits, the research activity in OCT has not taken much attention until recently. However the situation in Korea is gradually changing due to understanding of its versatile applications. Active research and commercialization are underway. Bulk optics-based OCT system is changed into alignfree fiber-optics system. With our expertise in the fabrication of fiber grating devices and strong background in control of fiber based system, we hope to contribute in developing simplified all-fiber OCT system with better performance. As a leading research group, working on OCT, we have firstly implemented fiber-based OCT system in Korea and demonstrated the imaging performance with glass plate and onion.     

Imaging through scattering medium by recording 3D “spatial-frequential” interferograms

Speed acquisition for image formation process through scattering medium is a challenge in optical coherence tomography (OCT) approach. Besides time domain (TD), spectral Fourier domain (FD) is now widely studied. By using a swept laser source, we demonstrate that a particular time domain OCT method (optical SISAM correlator) can be simultaneously implemented in a single set-up with the corresponding Fourier domain OCT approach (spectral interferometry). Then, FD-OCT and TD-OCT signals are obtained by processing a 3D “spatial-frequential” interferences pattern. We show that these two numerical approaches can be complementary when imaging in scattering medium is achieved.     

飞秒互相关时间选通技术用于光学层析成像的实验研究

利用飞秒互相关二次谐波信号时间选通技术。实现了对埋藏在高度散射介质中物体的透射成像和反射以析成像。互相关选通门有效地选出携带物体信息的弹道光子和蛇行光子，排除了给成像带来背景噪声的温射光子，分别获得了散射介质中物体的二次谐波一维和二维图像。     

光学相干层析系统噪音分析(Ⅱ)——时域OCT和频域OCT

本文作为前文《光学相干层析系统噪音分析(I)》的后续,对时域OCT和频域OCT的噪音和灵敏度进行了详细的分析和计算,证明与时域OCT系统不同,频域OCT系统的信噪比与光源带宽和纵向扫描深度无关,频域OCT系统可以在高速率图像采集的情况下仍然保持探测系统的大动态范围.     

The potential optical coherence tomography in tooth bleaching quantitative assessment

In this paper, we report the outcomes from a pilot study on using OCT functional imaging method to evaluate and quantify color alteration in the human teeth in vitro. The image formations of the dental tissues without and with treatment 35% hydrogen peroxide were obtained by an OCT system at a 1310 nm central wavelength. One parameter for the quantification of optical properties from OCT measurements is introduced in our study: attenuate coefficient (μ). And the attenuate coefficient have significant decrease (p < 0.001) in dentine as well as a significant increase (p < 0.001) in enamel was observed during tooth bleaching process. From the experimental results, it is found that attenuate coefficient could be useful to assess color alteration of the human tooth samples. OCT has a potential to become an effective tool for the assessment tooth bleaching. And our experiment offer a now method to evaluate color change in visible region by quantitative analysis of the infrared region information from OCT.     

Signal Processing Scheme for Increasing System Resolution in Determination of the Scattering Position in an OCT System

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｉｔｉｓａｄｉｆｆｉｃｕｌｔａｎｄｃｈａｌｌｅｎｇｉｎｇｐｒｏｂｌｅｍｉｎｍｏｄｅｒｎｏｐｔｉｃａｌｔｅｃｈｎｏｌｏｇｙｔｏｏｂｔａｉｎｔｈｅｎｏｎｉｎｖａｓｉｖｅｎｅａｒｉｎｆｒａｒｅｄｉｍａｇｉｎｇｏｆｍｉｃｒｏｓｔｒｕｃｔｕｒｅｉｎｏｂｓｃｕｒｅｍｅｄｉａｄｕｅｔｏｔｈｅｅｘｉｓｔｅｎｃｅｏｆｍｕｌｔｉｐｌｅｓｃａｔｔｅｒｉｎｇ ,ｗｈｉｃｈｄｅｇｒａｄｅｓｔｈｅｃｏｎｔｒａｓｔａｎｄｓｐａｔｉａｌｒｅｓｏｌｕｔｉｏｎｏｆｉｍａｇｉｎｇ ｇｒｅａｔｌｙ[1,2 ] .Ｏ…     

Signal Processing Scheme for Increasing System Resolution in Determination of the Scattering Position in an OCT System

In an OCT sensing system, the optical coherence length of the light source determines the spatial resolution, which is within the range of tens of micrometers. In this paper, by removing high-frequency noise with average operation and fitting the measured discrete sampled data with a continuous function, the theoretical resolution can be improved. The experimental results obtained show the short-term repeatability to be better than 0.4 μm after signal processing.     

Correlation characteristics of optical coherence tomography images of turbid media with statistically inhomogeneous optical parameters

Noisy structure of optical coherence tomography (OCT) images of turbid medium contains information about spatial variations of its optical parameters. We propose analytical model of statistical characteristics of OCT signal fluctuations from turbid medium with spatially inhomogeneous coefficients of absorption and backscattering. Analytically predicted correlation characteristics of OCT signal from spatially inhomogeneous medium are in good agreement with the results of correlation analysis of OCT images of different biological tissues. The proposed model can be efficiently applied for quantitative evaluation of statistical properties of absorption and backscattering fluctuations basing on correlation characteristics of OCT images.     

Determination of optical properties of oxidative bleaching human dental tissue samples using optical coherence tomography

Oxidative bleaching changes of human teeth induced changes in the optical properties of dental tissue. We introduced 1310 nm wavelengths of optical coherence tomography (OCT) attenuation coefficient method which is a relatively novel and rarely reported methodology to measure the correlation coefficient during the teeth oxidative bleaching procedure. And the quantitative parameters of enamel optical thickness and disruption of the entrance signal (DES) were extracted from the OCT images. The attenuation coefficient of the bleached tissue is 6.2 mm⁻¹ which is significant (p < 0.001) higher than that unbleached sample is 1.4 mm⁻¹. But attenuation coefficient varied significantly (p < 0.001) between 5.9 and 1.5 mm⁻¹ in dentine which is downtrend. Furthermore, the persistence of bleaching oxidation in 35% hydrogen peroxide-induced optical thickness of enamel is similar with unbleached tissue which may indicate the refractive index of enamel is unchanged. Moreover, disruption of the entrance signal (DES) analysis showed that remarkable difference was appeared at enamel surface. The results indicate that optical properties of oxidative bleaching human dental tissue can be determined by attenuation coefficient using OCT system.     

Phase-only filtering based on sliced orthogonal nonlinear generalized decomposition

The sliced orthogonal nonlinear generalized (SONG) decomposition and correlation have been demonstrated to be powerful tools in digital image processing and promising for nonlinear optical information processing. In this paper, we propose an optical phase-only filtering system based on SONG decomposition (PBS), in which the phase-only filtering of the target and the input scene binary slices are performed separately by pairs and then added together. We numerically show that the PBS has extremely high and sharp output correlation peak compared with other optical correlators. Furthermore, such a SONG decomposition based phase-only filtering naturally inherits the nature of SONG decomposition, which has strong robustness to additive Gaussian noise and substitutive noise, and also the high light efficiency of phase-only filtering. We demonstrate that the PBS may serve as an optimized optical correlation scheme, which is promising in nonlinear optical pattern recognition.     

超短脉冲激光电子学全息选通透过散射介质成象系统的噪音分析

本文详细分析了超短脉冲激光电子学全息选通透过散射介质成象系统的噪音因素,其噪音来源主要有电子学全息图的记录过程、再现过程以及CCD自身的噪音、系统光学元件产生的噪音等等,提出了相应的噪音处理措施.     

低相干光学层析技术中扫描装置的研究与设计

低相干光学层析技术是一种新型生物医学成象技术,具有快速、非侵入及高分辨的特点。本文在深入研究该技术原理的基础上,对实现该技术的关键环节-扫描装置进行了设计,并对该装置进行了实验验证,最后对实验结果进行了分析.     

Optical-fiber-based Mueller optical coherence tomography

An optical-fiber-based multichannel polarization-sensitive Mueller optical coherence tomography (OCT) system was built to acquire the Jones or Mueller matrix of a scattering medium, such as biological tissue. For the first time to our knowledge, fiber-based polarization-sensitive OCT was dynamically calibrated to eliminate the polarization distortion caused by the single-mode optical fiber in the sample arm, thereby overcoming a key technical impediment to the application of optical fibers in this technology. The round-trip Jones matrix of the sampling fiber was acquired from the reflecting surface of the sample for each depth scan (A scan) with our OCT system. A new rigorous algorithm was then used to retrieve the calibrated polarization properties of the sample. This algorithm was validated with experimental data. The skin of a rat was imaged with this fiber-based system.     

基于受激辐射信号的谱域光学相干层析分子成像方法

鉴于不同生理病理状态下组织复折射率实部的变化不大,传统光学相干层析(OCT)成像技术在分子特异性识别上存在先天不足.为此,本文提出了基于受激辐射信号的OCT成像方法,可在实现传统散射成像的同时,实现基于受激辐射信号的分子成像.在超高分辨率谱域OCT系统的基础上,通过增设光谱分光与调制抽运光支路,建立了基于单宽谱光源的抽运探测谱域OCT系统,详细推导了调制抽运下受激辐射信号的获取与成像公式.利用搭建的抽运探测谱域OCT系统,实现了瞬态受激辐射信号的相干探测.基于同时获取的受激辐射OCT信号和传统OCT信号,成功重构了氮化物粉末构建样品的基于受激辐射信号的分子对比OCT图像.