Feasibility of optical computerized tomography for measuring the species concentration distribution of flow fields

In this paper, the feasibility of using optical computerized tomography (OCT) methods for measuring the distribution of species concentration for flow fields is analyzed and discussed. First, feasible methods are chosen for two or three objects composed flow fields from the perspective of the measurable principle. Second, both common gas and plasma are chosen as two typical examples for specific analysis and discussion. The results show that the feasibility and applicable range of OCT methods are related to the temperature, pressure, and species composition of the measured flow fields. Finally, the study indicates that OCT methods are more suitable for measuring the distribution of species composition for common gas rather than plasma. In a word, this study could be helpful for extending the applicable range of OCT methods, which are based on the measurement of the refractive index.     

光学相干层析成像轴向超分辨研究

为了提高光学相干层析成像(OCT)的轴向分辨率,采用OCT与光学超分辨术相结合的方法,设计了三区相位型和振幅型两种光瞳滤波器,并将制作的光瞳滤波器应用于系统的样品臂中,分别测量不同条件下对应的轴向响应曲线,结果与理论分析基本吻合,实现了轴向分辨率10％以上的提高,从而验证了利用合适光瞳滤波器实现OCT轴向超分辨的可行性.     

Quantitative assessment of touch-screen panel by nondestructive inspection with three-dimensional real-time display optical coherence tomography

We investigated the use of optical coherence tomography (OCT) to measure several materials immersed in optical adhesives. The effects of variations in the concentration, physical characteristics, and thickness of the materials were studied, and these parameters were found to significantly affect the OCT measurement. The materials were selected for their distinct spectral properties in the infrared region. To ensure reliability, we acquired images using a scanning electron microscope after performing the semiconductor production process. We verified the feasibility of the application of OCT for defect inspection and product verification of touch-screen panels.     

Integrated multimodal endomicroscopy platform for simultaneous en face optical coherence and two-photon fluorescence imaging

We report an all-fiber-optic scanning, multimodal endomicroscope capable of simultaneous optical coherence tomography (OCT) and two-photon fluorescence (TPF) imaging. Both imaging modalities share the same miniature fiber-optic scanning endomicroscope, which consists of a double-clad fiber with a core operating in single mode at both the OCT (1310 nm) and two-photon excitation (1550 nm) wavelengths, a piezoelectric two-dimensional fiber-optic beam scanner, and a miniature aspherical compound lens suitable for simultaneous acquisition of en face OCT and TPF images. A fiber-optic wavelength division multiplexer was employed in the integrated platform to combine the low coherence OCT light source and the femtosecond two-photon excitation laser into the same optical path. Preliminary imaging results of cell cultures and mouse tissue ex vivo demonstrate the feasibility of simultaneous real-time OCT and TPF imaging in a scanning endomicroscopy setting for the first time.     

Measurement of crater geometries after laser ablation of bone tissue with optical coherence tomography

The feasibility of measuring crater geometries by use of optical coherence tomography (OCT) is examined. Bovine shank bone on a motorized translation stage with a motion velocity of 3 mm/s is ablated with a pulsed CO2 laser in vitro. The laser pulse repetition rate is 60 Hz and the spot size on the tissue surface is 0.5 mm. Crater geometries are evaluated immediately by both OCT and histology methods after laser irradiation. The results reveal that OCT is capable of measuring crater geometries rapidly and noninvasively as compared to histology. There are good correlation and agreement between crater depth estimates obtained by two techniques, whereas there exists distinct difference between crater width estimates when the carbonization at the sides of craters is not removed.     

Three-dimensional non-destructive optical evaluation of laser-processing performance using optical coherence tomography

We demonstrate the use of optical coherence tomography (OCT) as a non-destructive diagnostic tool for evaluating laser-processing performance by imaging the features of a pit and a rim. A pit formed on a material at different laser-processing conditions is imaged using both a conventional scanning electron microscope (SEM) and OCT. Then using corresponding images, the geometrical characteristics of the pit are analyzed and compared. From the results, we could verify the feasibility and the potential of the application of OCT to the monitoring of the laser-processing performance.     

Extraction of optical scattering parameters and attenuation compensation in optical coherence tomography images of multilayered tissue structures

A recently developed analytical optical coherence tomography (OCT) model [Thrane et al., J. Opt. Soc. Am. A 17, 484 (2000)] allows the extraction of optical scattering parameters from OCT images, thereby permitting attenuation compensation in those images. By expanding this theoretical model, we have developed a new method for extracting optical scattering parameters from multilayered tissue structures in vivo. To verify this, we used a Monte Carlo (MC) OCT model as a numerical phantom to simulate the OCT signal for heterogeneous multilayered tissue. Excellent agreement between the extracted values of the optical scattering properties of the different layers and the corresponding input reference values of the MC simulation was obtained, which demonstrates the feasibility of the method for in vivo applications. This is to our knowledge the first time such verification has been obtained, and the results hold promise for expanding the functional imaging capabilities of OCT.     

Feasibility of glucose monitoring based on Brownian dynamics in time-domain optical coherence tomography

Our purpose is to investigate the feasibility of Brownian motion in time-domain optical coherence tomography (OCT) incorporated with wavelet power spectrum to monitor glucose concentration in Intralipid solution. The results show that the standard deviation (SD) of frequency in the superficial layer of single scattering region, linearly proportional to Brownian diffusion coefficient, is independent of the depth. Our preliminary results demonstrate that average SD of frequency in the single scattering region is inversely proportional to the glucose concentration in Intralipid solution, since the Brownian diffusion coefficient is a function of concentration. Thus the average SD of frequency in OCT signal is capable of differentiating the glucose concentration.     

Application of wide-field optical coherence tomography to monitoring of viability of rat brain in vivo

We investigated the feasibility of OCT in monitoring the viability of the brain. It was confirmed that after an overdose of pentobarbital sodium salt for an euthanasia, the OCT signal intensity increased before cardiac arrest and finally became 2.7 times, and by periodically changing the tissue temperature from 20 to 32 °C in vivo, average correlation coefficients between the ratio of signal intensity (RSI) and temperature were determined to be ?0:42 to ?0:50. RSI reversibly changed with subsequent variations of temperatures and finally increased rapidly just before cardiac arrest. These results indicate that RSI could correspond to decreases in viability.     

Analysis on the feasibility of optical tomography in measuring gas jet flow velocity

Enlightened by the wide application of optical computerized tomography (OCT) in various flow fields’ visualization and parameter measurement, the potential feasibility of it on measuring gas jet flow velocity is discussed in this paper. The dependence of flow velocity on flow field's refractive index and dynamic pressure is deduced initially. An argon gas jet flow is chosen as an example for experiment, and the refractive index measurement is achieved by moiré tomography, while the dynamic pressure is obtained by a pressure sensor. In a word, both the theoretical and experimental results prove that OCT could be feasible to obtain the flow velocity of gas jet flows.     

Optically deviated focusing method based high-speed SD-OCT for in vivo retinal clinical applications

The aim of this study is to provide accurately focused, high-resolution in vivo human retinal depth images using an optically deviated focusing method with spectral-domain optical coherence tomography (SD-OCT) system. The proposed method was applied to increase the retinal diagnosing speed of patients with various values of retinal distances (i.e., the distance between the crystalline eye lens and the retina). The increased diagnosing speed was facilitated through an optical modification in the OCT sample arm configuration. Moreover, the optical path length matching process was compensated using the proposed optically deviated focusing method. The developed system was mounted on a bench-top cradle to overcome the motion artifacts. Further, we demonstrated the capability of the system by carrying out in vivo retinal imaging experiments. The clinical trials confirmed that the system was effective in diagnosing normal and abnormal retinal layers as several retinal abnormalities were identified using non-averaged single-shot OCT images, which demonstrate the feasibility of the method for clinical applications.     

Simultaneous swept source optical coherence tomography of the anterior segment and retina using coherence revival

We report on an implementation of coherence revival-based heterodyne swept source optical coherence tomography that is capable of simultaneously imaging the anterior and posterior eye. A polarization-encoded sample arm was used to efficiently focus orthogonal polarizations on the anterior segment and retina. Depth encoding was achieved using coherence revival, which allows for multiple depths within a sample to be simultaneously imaged and frequency encoded by carefully controlling the optical pathlength of each sample path. This design is a significant step toward whole-eye optical coherence tomography (OCT), which would enable customized ray-traced modeling of patient eyes to improve refractive surgical interventions and eliminate optical artifacts in retinal OCT diagnostics. We demonstrated the feasibility of this system for in vivo imaging by simultaneously acquiring images of the anterior segments and retinas in healthy human volunteers.     

Ball lens based lensed patch cord probes for optical coherence tomography in the field of dentistry

A lensed patch cord probe has been made with a ball lens packaged in a metal cylinder. By simply placing a ball lens directly in front of a fiber patch cord, a compact and potentially disposable sampling probe for optical coherence tomography (OCT) could be implemented. To achieve a sufficiently long working distance and a good transverse resolution simultaneously, the proper ball lens diameter and the distance between the ball lens and the fiber patch cord were investigated. Experimentally, a working distance of up to 5.2 mm, 3 dB bandwidth of 2 mm, and transverse resolution of 16 μm were achieved. With the patch cord probe, a common path swept source OCT system was implemented and used to demonstrate the feasibility as the dedicated probe for dentistry.     

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.     

OCT技术在发育生物学中的应用

基于光学低相干反射测量而发展起来的光学相干层析技术（ Optica1 Coherence Tomography,OCT）是一种新型的成像技术，它可以对强散射介质如生物组织实施非侵入性的快速活体成像。与传统的组织切片相比,OTC可以大大减少对发育形态成像所需的时间、复杂程度及成本。非接触和非侵入式的成像方式有助于研究个体发育中由基因变异所引起的形态和功能变化，因而在发育生物学的研究当中有着广阔的应用前景。概述了OCT技术在发育生物学当中诸方面的应用情况。     

Optical coherence tomography with plasmon resonant nanorods of gold

We explored plasmon resonant nanorods of gold as a contrast agent for optical coherence tomography (OCT). Nanorod suspensions were generated through wet chemical synthesis and characterized with spectrophotometry, transmission electron microscopy, and OCT. Polyacrylamide-based phantoms were generated with appropriate scattering and anisotropy coefficients (30 cm(-1) and 0.89, respectively) to image distribution of the contrast agent in an environment similar to that of tissue. The observed signal was dependent on whether the plasmon resonance peak overlapped the source bandwidth of the OCT, confirming the resonant character of enhancement. Gold nanorods with plasmon resonance wavelengths overlapping the OCT source yielded a signal-to-background ratio of 4.5 dB, relative to the tissue phantom. Strategies for OCT imaging with nanorods are discussed.     

基于比较测量法的光学电流互感器

提出采用永久磁体作为参考源应用于光学电流互感器中,对随环境因素改变的材料Verdet常数及线性双折射进行实时补偿的比较测量法.运用矩阵光学理论对该方法进行了理论分析,并进行了相关实验,实验结果证明了该方法的可行性.设计的传感单元采用了点式传感头,具有结构简单的特点,适合于在高电压环境中应用.     

Combined Raman spectroscopy and optical coherence tomography device for tissue characterization

We report a dual-modal device capable of sequential acquisition of Raman spectroscopy (RS) and optical coherence tomography (OCT) along a common optical axis. The device enhances application of both RS and OCT by precisely guiding RS acquisition with OCT images while also compensating for the lack of molecular specificity in OCT with the biochemical specificity of RS. We characterize the system performance and demonstrate the capability to identify structurally ambiguous features within an OCT image with RS in a scattering phantom, guide acquisition of RS from a localized malignancy in ex vivo breast tissue, and perform in vivo tissue analysis of a scab.     

Dual-modality photothermal optical coherence tomography and magnetic-resonance imaging of carbon nanotubes

We demonstrate polyethylene-glycol-coated single-walled carbon nanotubes (CNTs) as contrast agents for both photothermal optical coherence tomography (OCT) and magnetic-resonance imaging (MRI). Photothermal OCT was accomplished with a spectral domain OCT system with an amplitude-modulated 750 nm pump beam using 10 mW of power, and T(2) MRI was achieved with a 4.7 T animal system. Photothermal OCT and T(2) MRI achieved sensitivities of nanomolar concentrations to CNTs dispersed in amine-terminated polyethylene glycol, thus establishing the potential for dual-modality molecular imaging with CNTs.     

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.