Compression as a method for increasing the informativity of optical coherence tomography of biotissues

The efficiency of the mechanical compression of biotissues for improving the differentiation between pathological changes in the structure of a biotissue observed by the method of optical coherence tomography (OCT) is investigated. The effect of the compression in the OCT-images of samples of the human rectum affected by inflammation and carcinoma is studied ex vivo. It is shown that the use of compression makes it possible to differentiate between these pathological changes. To interpret experimental data, images of an inflamed part of rectum are modeled by the Monte Carlo method for different degrees of compression. The results of modeling agree qualitatively with the experimental data.     

Imaging of human breast tissue using polarization sensitive optical coherence tomography

We report a study on the use of polarization sensitive optical coherence tomography (PSOCT) for discriminating malignant (invasive ductal carcinoma), benign (fibroadenoma) and normal (adipocytes) breast tissue sites. The results show that while conventional OCT, that utilizes only the intensity of light back-scattered from tissue microstructures, is able to discriminate breast tissues as normal (adipocytes) and abnormal (malignant and benign) tissues, PS-OCT helps in discriminating between malignant and benign tissue sites also. The estimated values of birefringence obtained from the PSOCT imaging show that benign breast tissue samples have significantly higher birefringence as compared to the malignant tissue samples.     

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.     

Real-time measurement of in vitro flow by Fourier-domain color Doppler optical coherence tomography

The possibility of measuring a full Doppler flow depth profile in parallel by use of frequency-domain optical coherence tomography is demonstrated. The method is based on a local phase analysis of the backscattered signal and allows for imaging of bidirectional Doppler flow. The Doppler frequency limit is 5 kHz for the presented measurements and is set by half of the frame rate of the CCD detector array. We measured the flow of 0.3-microm microspheres suspended in distilled water at controlled flow rates and in vitro human blood flow through a 200-microm capillary with a real-time color-encoded Doppler tomogram rate of 2-3/s.     

Simulation of polarization-sensitive optical coherence tomography images by a Monte Carlo method

We introduce a new Monte Carlo (MC) method for simulating optical coherence tomography (OCT) images of complex multilayered turbid scattering media. We demonstrate, for the first time of our knowledge, the use of a MC technique to imitate two-dimensional polarization-sensitive OCT images with nonplanar boundaries of layers in the medium like a human skin. The simulation of polarized low-coherent optical radiation is based on the vector approach generalized from the iterative procedure of the solution of Bethe-Saltpeter equation. The performances of the developed method are demonstrated both for conventional and polarization-sensitive OCT modalities.     

Determination of local polarization properties of biological samples in the presence of diattenuation by use of Mueller optical coherence tomography

A unique feature of polarization-sensitive Mueller optical coherence tomography is that, by measuring Jones or Mueller matrices, it can reveal the complete polarization properties of biological samples, even in the presence of diattenuation. We map local polarization properties for the first time to our knowledge by using polar decomposition in combination with least-squares fitting to differentiate measured integrated Jones matrices with respect to depth. We also introduce the new concept of dual attenuation coefficients to characterize diattenuation per unit infinitesimal length in tissues. We experimentally verify the algorithm using measurements of a section of porcine tendon and the septum of a rat heart.     

High-speed polygon-scanner-based wavelength-swept laser source in the telescope-less configurations with application in optical coherence tomography

A compact high-speed tuning laser source is demonstrated in two different configurations using a polygonal mirror scanner without a telescope. It is shown that the filter configuration finesse increases by utilizing multiple reflections from the polygon facet(s) and grating illumination(s). Theoretically, the free spectral range (FSR), the instantaneous linewidth, and the finesse of each filter configuration are derived. For single grating illumination, the measured coherence length, FSR, and power were 2.8 mm, 184 nm, and 40 mW at the scanning frequency of 50 kHz, respectively. Coherence length, FSR, and power of the second laser configuration were 6.2 mm, 117 nm, and 35 mW, respectively. Finally, images of a human finger were acquired in vivo using two proposed swept-source configurations.     

Experimental studies of polarization of laser radiation in a rotating optical glass

The results of experiments on observation of rotation of the plane of polarization of coherent laser radiation with wavelength λ = 0.632991 μm after propagation through a rotating optical disk made of TF3 glass with refractive index n = 1.71250 are analyzed. The experiments were conducted at angle of ray incidence on the flat disk surface ?₀ = 60°, and the rotational speed of the disk was varied from 0 to 200 Hz in both directions. The results indicate that rotation of optically transparent, homogeneous, and isotropic dielectric causes rotation of linear polarization of the monochromatic electromagnetic plane wave by several tens of degrees. At a rotational speed of 3 Hz, the rotation of polarization reached Δφ = 70° for the vertical component of laser output polarization. The dependences of the angle of rotation of polarization and the degree of polarization of the rays on rotational speed are nonlinear and are attributed to the appearance of substantial anisotropic properties in a rotating dielectric.     

激光法红外热像镜组中心偏测量与调校研究

论述了多镜片成像光学镜组中心偏的理论表征 ,以及自准反射旋转法测量中心偏的原理。设计了用于红外光学镜组的中心偏检测系统。系统包括用于 8～ 14 μm红外光学系统中心偏测量的CO2 激光 ;可调焦望远镜 ;采用TGS热释电热像仪与计算机配合的数据读出及处理系统 ;径向跳动≤ 1μm ,轴向晃动≤ 1″的高精密基准轴工作台。系统测量中心偏精度为 :角度≤ 2″ ,线度≤ 0 .0 2mm。给出了中心偏数据处理程序。系统也可用于在线装校 ,更换光源 (用He Ne激光代替CO2 激光 )系统可用于 3～ 5 μm红外光学系统的测量。进一步改进并利用激光的相干特性 ,系统可实现中心偏测量精度≤ 1μm。     

Effect of coherence and polarization on resolution of optical imaging system

The effect of coherence properties of illumination on image resolution, well known in a scalar case, is studied for the case of vector electromagnetic illumination. Using an example of vector Gaussian Schell-model illumination, we analyze the dependence of optical system resolution on the transverse correlation lengths of the orthogonal field components and on the ratio of the powers of these components, each taken separately.     

Statistics and reduction of speckle in optical coherence tomography

Studies have shown that optical coherence tomography (OCT) is useful in imaging microscopic structures through highly scattering media. Because spatially coherent light is used in OCT, speckle in the reconstructed image is unavoidable, resulting in degradation of the quality of the OCT images and impaired ability to differentiate subsurface structures. Therefore speckle reduction is an important issue in OCT imaging. We develop speckle statistics that are appropriate to the OCT measurements and demonstrate a simple and practical speckle-reduction technique.     

Suppression of image artifacts in the spectral-domain optical coherence tomography

In this paper, we review methods for obtaining in vivo optical images of bio-objects with the resolution ranged from several units to tens of micrometers, namely, the methods of spectral-domain optical coherence tomography. We focus on problems that are specific of the spectral-domain optical coherence tomography, namely, the presence of coherent noise and mirror-symmetric phantoms in the image. On the basis of the most important relevant publications, we analyze possibilities of eliminating these drawbacks in modern devices.     

Effect of coherence and polarization on frequency resolution in optical Fourier transforming system

Using an example of vector Gaussian Schell-model beam, we demonstrate and analyze the dependence of the spatial frequency resolution in optical Fourier transforming system on the intrinsic coherence-polarization structure of illumination.     

Effect of polarization and coherence of low-intensity optical radiation on fish embryos

  We have shown that brief exposure of sturgeon embryos (fertilized roe) in the organogenesis stage to low-intensity radiation in the visible region of the spectrum can have a long-term effect on embryonic and post-embryonic development of the fish, detectable 50 days after the irradiation procedure. The biological effects (size-weight characteristics and hardiness parameters of the fish relative to unfavorable habitat conditions) induced by linearly polarized emission from a monochromatic laser source (helium-neon laser, λ = 632.8 nm, Δλ ≈ 0.02 nm) and a quasi-monochromatic light-emitting diode (LED) source (maximum in emission spectrum λ = 631 nm, Δ λ = 15 nm) are practically the same. Going to broadband linearly polarized radiation (λ = 420–800 nm) is accompanied by a decrease in the biological effect. From the results of studies of the effect on embryos from linearly polarized and unpolarized radiation from an LED source and also the effect of linearly polarized, circularly polarized, and unpolarized radiation from a helium-neon laser, we concluded that the type of polarization is of critical importance in realization of the biological effect of radiation. In this case, the maximum stimulating effect (on the size×weight characteristics and the hardiness parameters for juvenile fish) is observed on exposure to linearly polarized radiation; the photobiological effect induced in the same dose range by light with natural polarization (i.e., unpolarized) is significantly less pronounced; the stimulating effect of circularly polarized radiation occupies an intermediate position. Based on the presented data and also on data obtained previously, we conclude that among the resonant and nonresonant photophysical processes (orientational effect of light, effect of gradient forces, dipole-dipole interactions, thermooptic processes) capable of inducing photobiological effects dependent on such laser-specific characteristics as polarization and coherence, the determining influence in the processes studied in this work comes from the orientational effect of light and dipole×dipole interactions. And the orientational effect can appear for anisotropic media with liquid-crystal type ordering (especially domains in membranes and multiple-enzyme complexes) both under conditions when there is no resonant absorption and for weakly absorbing structures, and can initiate a change in their conformations and accordingly their functional characteristics. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 843–858, November–December, 2008.     

Resolution improvement in optical coherence tomography by optimal synthesis of light-emitting diodes

We present a new approach to improving the longitudinal resolution of optical coherence tomography by optimal synthesis of several LED's. The search for an optimal synthesis of several low-coherence sources involves solution of an inverse problem, and an optimization algorithm is introduced that is used to arrange the parameters of light sources to effectively reduce the width of the center peak and inhibit the sidelobes simultaneously. Good coincidence between the experimental result and theoretical expectation is found.     

Molecular contrast in optical coherence tomography by use of a pump-probe technique

We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.     

Depth-resolved monitoring of glucose diffusion in tissues by using optical coherence tomography

We demonstrate the capability of the optical coherence tomography (OCT) technique for depth-resolved monitoring and quantifying of glucose diffusion in fibrous tissues (sclera). The depth-resolved and average permeability coefficients of glucose were calculated. We found that the glucose diffusion rate is not uniform throughout the tissue and is increased from approximately 2.39+/-0.73 x 10(-6) cm/s at the epithelial side to 8.63+/-0.27 x 10(-6) cm/s close to the endothelial side of the sclera. Results demonstrated that the OCT technique is capable of depth-resolved monitoring and quantification of glucose diffusion in sclera with a resolution of approximately 40 mum.     

Synthesized optical coherence tomography for imaging of scattering objects by use of a stepwise frequency-modulated tunable laser diode

A technique named synthesized optical coherence tomography (SOCT) has been proposed and developed as an alternative method to the well-known optical coherence tomography for cross-sectional imaging of scattering objects. SOCT is based on the principle of synthesis of an optical coherence function by use of a tunable laser diode. With stepwise frequency modulation of light and synchronous phase modulation, the coherence function is synthesized into a peak at an arbitrary location. The longitudinal scattering distribution of the object under test is thus obtained without a mechanically driven reference. Two-dimensional tomography was demonstrated in a basic experiment with a lateral mechanical scan.     

High-flow-velocity and shear-rate imaging by use of color Doppler optical coherence tomography

Color Doppler optical coherence tomography (CDOCT) is capable of precise velocity mapping in turbid media. Previous CDOCT systems based on the short-time Fourier transform have been limited to maximum flow velocities of the order of tens of millimeters per second. We describe a technique, based on interference signal demodulation at multiple frequencies, to extend the physiological relevance of CDOCT by increasing the dynamic range of measurable velocities to hundreds of millimeters per second. The physiologically important parameter of shear rate is also derived from CDOCT measurements. The measured flow-velocity profiles and shear-rate distributions correlate very well with theoretical predictions. The multiple demodulation technique, therefore, may be useful to monitor blood flow in vivo and to identify regions with high and low shear rates.