Mapping local retardance in birefringent samples using polarization sensitive optical coherence tomography

We proposed a method to extract depth-resolved local retardance in birefringent samples from conventional polarization-sensitive optical coherence tomography (PSOCT) that uses one circularly polarized incident light. Despite the wide use of such PSOCT systems in characterizing birefringent samples, the measured cumulative retardance does not represent the true cumulative retardance when optical axis varies with depth. A Jones calculus based algorithm was designed to derive the local depth-resolved retardance from conventional cumulative PSOCT results. The algorithm was tested in samples with homogeneous optical axis as well as samples with depth-dependent optical axis.     

Molecularly sensitive optical coherence tomography

Molecular contrast in optical coherence tomography (OCT) is demonstrated by use of coherent anti-Stokes Raman scattering (CARS) for molecular sensitivity. Femtosecond laser pulses are focused into a sample by use of a low-numerical-aperture lens to generate CARS photons, and the backreflected CARS signal is interferometrically measured. With the chemical selectivity provided by CARS and the advanced imaging capabilities of OCT, this technique may be useful for molecular contrast imaging in biological tissues. CARS can be generated and interferometrically measured over at least 600 microm of the depth of field of a low-numerical-aperture objective.     

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.     

Imaging needle for optical coherence tomography

We describe a miniature optical coherence tomography (OCT) imaging needle that can be inserted into solid tissues and organs to permit interstitial imaging of their internal microstructures with micrometer scale resolution and minimal trauma. A novel rotational coupler with a glass capillary tube is also presented that couples light from a rotating single-mode fiber to a stationary one. A prototype needle with a 27-gauge (~410-mum) outer diameter has been developed and is demonstrated for in vivo imaging. The OCT needle can be integrated with standard excisional biopsy devices and used for OCT-guided biopsy.     

光学相干层析术用于鲜红斑痣诊断

光学相干层析术(optical coherence tomography,简称OCT)具有非侵入性,高分辨及高速成像的优点,特别适合于生物医学领域。但由于大部分生物组织具高散射系数,通常仅能对表层组织下数毫米深度内进行成像。穿透深度不足限制了OCT在皮肤科等领域应用。作为常见多发病的鲜红斑痣具有病变组织浅,血管增生明显等特点,所以OCT非常适于鲜红斑痣的检测。通过选择皮肤穿透性好的中心波长为1310nm超辐射二极管,合理优化样品臂和参考臂光强比例及偏振控制,实现了对鲜红斑痣在体成像研究,采集了清晰的OCT图像,得到其关键特征参数,如表皮层厚度,血管直径等,对鲜红斑痣的诊断及制定合理治疗方案具有重要意义。     

Imaging magnetically labeled cells with magnetomotive optical coherence tomography

We introduce a novel contrast mechanism for optical coherence tomography (OCT) whereby the optical scattering of magnetically labeled cells is modified by means of an externally applied magnetic field. This modification is made through the addition of a small electromagnet to the imaging arm of a conventional OCT interferometer. We measure the magnetomotive OCT signal by differencing pairs of axial scans (A-scans) acquired with the magnetic field on and off. Magnetomotive contrast is demonstrated in bulk three-dimensional cell scaffolds containing macrophages labeled with microparticles of iron oxide, demonstrating magnetic-specific contrast over a dynamic range of 30 dB.     

Imaging and velocimetry of the human retinal circulation with color Doppler optical coherence tomography

Noninvasive monitoring of blood flow in retinal microcirculation may elucidate the progression and treatment of ocular disorders, including diabetic retinopathy, age-related macular degeneration, and glaucoma. Color Doppler optical coherence tomography (CDOCT) is a technique that allows simultaneous micrometer-scale resolution cross-sectional imaging of tissue microstructure and blood flow in living tissues. CDOCT is demonstrated for the first time in living human subjects for bidirectional blood-flow mapping of retinal vasculature.     

Cross-polarized backscatter in optical coherence tomography of biological tissue

We have observed that cross-polarized backscatter measured by optical coherence tomography of human skin in vivo is surprisingly strong. We identify and give evidence of its main origins: single scattering from nonspherical particles and multiple scattering by particles with sizes much larger than a wavelength. Our findings show that depolarized light scattered by dense large-diameter particles maintains a high degree of temporal coherence and that differential-polarization imaging improves contrast between particles of different sizes.     

Quantifying tissue microvasculature with speckle variance optical coherence tomography

In this Letter, we demonstrate high resolution, three-dimensional optical imaging of in vivo blood vessel networks using speckle variance optical coherence tomography, and the quantification of these images through the development of biologically relevant metrics using image processing and segmentation techniques. Extracted three-dimensional metrics include vascular density, vessel tortuosity, vascular network fractal dimension, and tissue vascularity. We demonstrate the ability of this quantitative imaging approach to characterize normal and tumor vascular networks in a preclinical animal model and the potential for quantitative, longitudinal vascular treatment response monitoring.     

基于相位敏感谱域光学相干层析术的潜指纹获取方法

本文提出一种基于相位敏感谱域光学相干层析术 (spectral domain optical coherence tomography, SD-OCT) 的遗留指纹获取方法, 该方法具有非接触、无损、快速和高灵敏度优势. 实验结果显示, 即使在低对比度条件下, 本方法也能较好地再现遗留指纹, 证明相位敏感谱域光学相干层析术可以准确、可靠地识别潜指纹. 关键词： 潜指纹 谱域光学相干层析术 相位敏感     

Parallel optical coherence tomography using a CCD camera

Parallel optical coherence tomography is demonstrated using a 12-bit scientific-grade charge-coupled device array.A superluminescent diode in combination with a free-space Michelson interferometer was employed to achieve 10-μm axial resolution and 1.1-μm transverse resolution on a 902×575 μm2 field of view.We imaged a test mirror and bovine retinal tissue using a four-step phase shift method.     

Dental fiber-reinforced composite analysis using optical coherence tomography

An optical coherence tomography (OCT) system with 6 μm spatial resolution was employed to image the sites of fracture initiation and slow crack propagation in a fiber reinforced composite. Bar specimens (2 mm × 3 mm × 25 mm) of fiber reinforced composite were mechanically and thermally cycled to emulate oral conditions. The interior of the samples were analyzed prior and after the emulations. We analyzed the specimens that were intact after the loading cycling. The results demonstrated the capacity of the OCT technique to generate images of the sites fracture initiation, crack propagation, and regions surrounding the fracture, and it can be used in the future for quantitative analysis thus complementing other existing methods, with the main advantage of being non-destructive and non-invasive.     

Optical coherence tomography using a frequency-tunable optical source

We have developed a simple, wide-optical-bandwidth, high-resolution system for performing rapid optical frequency domain reflectometry measurements and applied it to multidimensional tomographic imaging. The source is a grating-tuned external cavity semiconductor laser with a tuning capability of 25 nm in 100 ms. We discuss system performance and show a two-dimensional optical coherence tomography image of a thin glass sandwich structure as a preliminary demonstration of the systems depth and resolution capabilities.     

Multi-channel spectral-domain optical coherence tomography using single spectrometer

Multi-channel detection is an effective way to improve data throughput of spectral-domain optical coherence tomography(SDOCT).However,current multi-channel OCT requires multiple detectors,which increases the complexity and cost of the system.We propose a novel multi-channel detection design based on a single spectrometer.Each camera pixel receives interferometric spectral signals from all the channels but with a spectral shift between two channels.This design effectively broadens the spectral ba...     

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.     

Tracking optical coherence tomography

An experimental tracking optical coherence tomography (OCT) system has been clinically tested. The prototype instrument uses a secondary sensing beam and steering mirrors to compensate for eye motion with a closed-loop bandwidth of 1 kHz and tracking accuracy, to within less than the OCT beam diameter. The retinal tracker improved image registration accuracy to <1 transverse pixel (<60 microm). Composite OCT images averaged over multiple scans and visits show a sharp fine structure limited only by transverse pixel size. As the resolution of clinical OCT systems improves, the capability to reproducibly map complex structures in the living eye at high resolution will lead to improved understanding of disease processes and improved sensitivity and specificity of diagnostic procedures.     

光学相干层析信号的模拟分析与计算

对传统的模拟介质散射响应函数的蒙特卡罗算法的计算过程进行了改进，提出光子不可分割的假设，这样可以避免人为选定光子被吸收阈值的不确定性；同时采用双曲线法模拟入射高斯光束，解决了对表面为非平面介质的传输信号进行模拟的问题.通过对盖玻片（平面）与眼角膜（曲面）的光学相干层析探测信号及层析图的数值模拟，并与相应实验结果进行比较，证实了该方法与假设的可行性. 关键词： 光学相干层析 蒙特卡罗法模拟 散射     

Fiber-optic-bundle-based optical coherence tomography

A fiber-optic-bundle-based optical coherence tomography (OCT) probe method is presented. The experimental results demonstrate this multimode optical fiber-bundle-based OCT system can achieve a lateral resolution of 12 microm and an axial resolution of 10 microm with a superluminescent diode source. This novel OCT imaging approach eliminates any moving parts in the probe and has a primary advantage for use in extremely compact and safe OCT endoscopes for imaging internal organs and great potential to be combined with confocal endoscopic microscopy.     

Spectroscopic optical coherence tomography

Spectroscopic optical coherence tomography (OCT), an extension of conventional OCT, is demonstrated for performing cross-sectional tomographic and spectroscopic imaging. Information on the spectral content of backscattered light is obtained by detection and processing of the interferometric OCT signal. This method allows the spectrum of backscattered light to be measured over the entire available optical bandwidth simultaneously in a single measurement. Specific spectral features can be extracted by use of digital signal processing without changing the measurement apparatus. An ultrabroadband femtosecond Ti:Al(2)O(3) laser was used to achieve spectroscopic imaging over the wavelength range from 650 to 1000 nm in a simple model as well as in vivo in the Xenopus laevis (African frog) tadpole. Multidimensional spectroscopic data are displayed by use of a novel hue-saturation false-color mapping.     

Second-harmonic optical coherence tomography

Second-harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical responses of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second-harmonic waves from collagen harvested from rat tail tendon and a reference non-linear crystal. Second-harmonic interference fringe signals were detected and used for image construction. Because of the strong dependence of second-harmonic generation on molecular and tissue structures, this technique imparts contrast and resolution enhancement to conventional optical coherence tomography.