1. Articles from Alexander A. Moiseev

    1-18 of 18
    1. Cross-polarization optical coherence tomography for brain tumor imaging

      Cross-polarization optical coherence tomography for brain tumor imaging

      This paper considers valuable visual assessment criteria for distinguishing between tumorous and non-tumorous tissues, intraoperatively, using cross-polarization OCT (CP OCT) – OCT with a functional extension, that enables detection of the polarization properties of the tissues in addition to their conventional light scattering. Materials and methods. The study was performed on 176 ex vivo human specimens obtained from 30 glioma patients. To measure the degree to which the typical parameters of CP OCT images can be matched to the actual histology, 100 images of tumors and white matter were selected for visual analysis to be undertaken by three “single-blinded” investigators. An ...

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    2. Time-related ex vivo changes in the optical properties of normal brain tissues

      Time-related ex vivo changes in the optical properties of normal brain tissues

      The aim of the study was to observe time-related changes in the optical properties of normal brain tissues as measured using cross-polarization optical coherence tomography (CP OCT). 32 ex vivo tissue samples from 16 animals (rats) were monitored under different external conditions, over a period of 1 hour after excision, to measure time-related optical changes. It was found that the optical properties of white matter were quite stable over the time scales of the experiments, while the optical properties of the gray matter could change significantly. However, these changes could be minimized by using fresh sections from samples that had ...

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    3. Optical coherence angiography without motion correction preprocessing

      Optical coherence angiography without motion correction preprocessing

      The method for vessel visualization from optical coherence tomography (OCT) data is presented. The method is based on high-frequency filtration of the normalized absolute values of the scattered field measured with OCT. It is shown that in contrast with optical coherence angiography based on the processing of complex values of a scattered field, the proposed processing does not require motion correction preprocessing while providing resulting angiographic images of comparable quality.

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    4. Quantitative nontumorous and tumorous human brain tissue assessment using microstructural co- and cross-polarized optical coherence tomography

      Quantitative nontumorous and tumorous human brain tissue assessment using microstructural co- and cross-polarized optical coherence tomography

      Optical coherence tomography (OCT) is a promising method for detecting cancer margins during tumor resection. This study focused on differentiating tumorous from nontumorous tissues in human brain tissues using cross-polarization OCT (CP OCT). The study was performed on fresh ex vivo human brain tissues from 30 patients with high- and low-grade gliomas. Different tissue types that neurosurgeons should clearly distinguish during surgery, such as the cortex, white matter, necrosis and tumorous tissue, were separately analyzed. Based on volumetric CP OCT data, tumorous and normal brain tissue were differentiated using two optical coefficients — attenuation and forward cross-scattering. Compared with white matter ...

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    5. Digital refocusing in optical coherence tomography using finite impulse response filters

      Digital refocusing in optical coherence tomography using finite impulse response filters

      A finite impulse response filter, which shifts the focal plane in optical coherence tomography (OCT) images, is proposed. Since several OCT images with the focal plane in various positions can be fused into one image with increased lateral resolution, such a filter facilitates the creation of an OCT system with numerically increased lateral resolution, operating in real-time, i.e. showing one OCT B-scan with increased lateral resolution while collecting data for the next B-scan. Since the proposed real-time resolution enhancement method is phase-sensitive, the method for estimating and compensating phase shifts between consecutive B-scans during data acquisition is also discussed.

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    6. Medium chromatic dispersion calculation and correction in spectral-domain optical coherence tomography

      Medium chromatic dispersion calculation and correction in spectral-domain optical coherence tomography

      A method for determining and correcting distortions in spectral-domain optical coherence tomography images caused by medium dispersion was developed. The method is based on analysis of the phase distribution of the interference signal recorded by an optical coherence tomography device using an iterative approach to find and compensate for the effect of a medium’s chromatic dispersion on point-spread function broadening in optical coherence tomography. This enables compensation of the impact of medium dispersion to an accuracy of a fraction of a radian (units of percent) while avoiding additional measurements and solution of the optimization problem. The robustness of the ...

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    7. Quantitative evaluation of atherosclerotic plaques using cross-polarization optical coherence tomography, nonlinear, and atomic force microscopy

      Quantitative evaluation of atherosclerotic plaques using cross-polarization optical coherence tomography, nonlinear, and atomic force microscopy

      A combination of approaches to the image analysis in cross-polarization optical coherence tomography (CP OCT) and high-resolution imaging by nonlinear microscopy and atomic force microscopy (AFM) at the different stages of atherosclerotic plaque development is studied. This combination allowed us to qualitatively and quantitatively assess the disorganization of collagen in the atherosclerotic arterial tissue (reduction and increase of CP backscatter), at the fiber (change of the geometric distribution of fibers in the second-harmonic generation microscopy images) and fibrillar (violation of packing and different nature of a basket-weave network of fibrils in the AFM images) organization levels. The calculated CP channel-related ...

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    8. Vessel-contrast enhancement in label-free optical coherence angiography based on phase and amplitude speckle variability

      Vessel-contrast enhancement in label-free optical coherence angiography based on phase and amplitude speckle variability

      Recently proposed in vivo label-free optical coherence angiography techniques based on phase and amplitude speckle variability often require additional signal pre- and post processing operations to enhance vessel-contrast. We observe here 1) contrast enhancement by optimizing the signal normalization/weighing before processing; 2) algorithm based on Kasai estimator for phase compensation between processed A-scans to reduce masking role of motion artifacts; and 3) image projection through the imaging depth for en face plotting. We demonstrate the efficiency of proposed additional algorithms as for the microcirculation imaging of hamsters cheek in vivo as for the preliminary microcirculation imaging of patients after ...

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    9. Characterization of atherosclerotic plaques by cross-polarization optical coherence tomography

      Characterization of atherosclerotic plaques by cross-polarization optical coherence tomography

      We combined cross-polarization optical coherence tomography (CP OCT) and non-linear microscopy based on second harmonic generation (SHG) and two-photon-excited fluorescence (2PEF) to assess collagen and elastin fibers in the development of the atherosclerotic plaque (AP). The study shows potential of CP OCT for the assessment of collagen and elastin fibers condition in atherosclerotic arteries. Specifically, the additional information afforded by CP OCT, related to birefringence and cross-scattering properties of arterial tissues, may improve the robustness and accuracy of assessment about the microstructure and composition of the plaque for different stages of atherosclerosis.

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    10. Correction of aberrations in digital holography using the phase gradient autofocus technique

      Correction of aberrations in digital holography using the phase gradient autofocus technique

      We propose a method for correcting aberrations in digital holography based on the principles of computational adaptive optics using the phase gradient autofocus technique that demands no reference measurements. The method requires a priori information on the relative positions of the elements of the optical setup. It is applicable for sufficiently smooth optical aberrations. This technique does not impose any restrictions on the magnitude of the scattered optical field phase distortions caused by the object structure. The efficacy of the proposed method is demonstrated through numerical simulation and experimental verification.

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    11. Multi-modal optical imaging characterization of atherosclerotic plaques

      Multi-modal optical imaging characterization of atherosclerotic plaques

      We combined cross-polarization optical coherence tomography (CP OCT) and non-linear microscopy based on second harmonic generation (SHG) and two-photon-excited fluorescence (2PEF) to assess collagen and elastin fibers and other vascular structures in the development of atherosclerosis, including identification of vulnerable plaques, which remains an important clinical problem and imaging application. CP OCT's ability to visualize tissue birefringence and cross-scattering adds new information about the microstructure and composition of the plaque. However its interpretation can be ambiguous, because backscattering contrast may have a similar appearance to the birefringence related fringes. Our results represent a step towards minimally invasive characterization and ...

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    12. Scan-pattern and signal processing for microvasculature visualization with complex SD-OCT: tissue-motion artifacts robustness and decorrelation time - blood vessel characteristics

      Scan-pattern and signal processing for microvasculature visualization with complex SD-OCT: tissue-motion artifacts robustness and decorrelation time - blood vessel characteristics

      We propose a modification of OCT scanning pattern and corresponding signal processing for 3D visualizing blood microcirculation from complex-signal B-scans. We describe the scanning pattern modifications that increase the methods’ robustness to bulk tissue motion artifacts, with speed up to several cm/s. Based on these modifications, OCT-based angiography becomes more realistic under practical measurement conditions. For these scan patterns, we apply novel signal processing to separate the blood vessels with different decorrelation times, by varying of effective temporal diversity of processed signals. 

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    13. Hybrid M-mode-like OCT imaging of 3D microvasculature in vivo using reference-free processing of complex-valued B-scans

      Hybrid M-mode-like OCT imaging of 3D  microvasculature in vivo using reference-free  processing of complex-valued B-scans

      We propose a novel OCT-based method for visualizing microvasculature in 3D using reference-free processing of individual complex-valued B-scans with highly overlapped A-scans. In the lateral direction of such a B-scan, the amplitude and phase of speckles corresponding to vessel regions exhibit faster variability, and thus can be detected without comparison with other B-scans recorded in the same plane. This method combines elements of several existing OCT angiographic approaches, and exhibits: (i) enhanced robustness with respect to bulk tissue motion with frequencies up to tens of Hz; (ii) resolution of microcirculation images equal to that of structural images and (iii) possibility ...

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    14. Noniterative method of reconstruction optical coherence tomography images with improved lateralresolution in semitransparent media

      Noniterative method of reconstruction optical coherence tomography images with improved lateralresolution in semitransparent media

      A method of OCT imaging with a resolution throughout the investigated volume equal to the resolution in the best-focused region is described. It is based on summation of three-dimensional scattered field distributions at the wavelengths determined by OCT source spectral decomposition. A method of finding parameters needed for algorithmic realization of the summation is also proposed. The proposed approaches are tested on several model media, including biological ones.

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    15. Feature Of The Week 4/1/12: Russian Institute of Applied Physics Investigates Digital Refocusing in Optical Coherence Tomography Systems

      Feature Of The Week 4/1/12: Russian Institute of Applied Physics Investigates Digital Refocusing in Optical Coherence Tomography Systems

      Over the past few years using electronic post optical detection processing to create a synthetic receiver field-of-view has become a very promising technique for offering improved performance in biomedical optical imaging systems. Various approaches around this basic theme have been used in OCT and non-OCT systems such as synthetic aperture radar, digital holography, and other microscopy techniques.  The approach not only allows for improving the classic depth-of-focus vs lateral resolution tradeoff in OCT systems but offers other promising performance enhancement such as eliminating the need for deformable mirrors in adaptive optics ophthalmic imaging and application benefits in other fields such ...

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    16. Digital refocusing in optical coherence tomography

      Digital refocusing in optical coherence tomography

      The problem of restoration Optical Coherence Tomography (OCT) images, acquired with tightly focused probing beam, in out-of-focus region for improving lateral resolution of the OCT has been considered. Phase stability issue has been discussed and phase equalization algorithm has been proposed. After phase equalization, the algorithm of digital refocusing, based on some methods from the DH, have been applied to the simulated as well as to experimental OCT data, acquired with tightly focused scanning beam to restore micrometer lateral resolution in the whole investigated volume.

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    17. Blind deconvolution algorithm for restoration OCT images with diffraction limited resolution

      Blind deconvolution algorithm for restoration OCT images with diffraction limited resolution
      In this paper we describe an algorithm which is able to compensate an unknown defocus. This algorithm has been applied to recovering defocused en-face Optical Coherence Tomography images. Lateral resolution about 5 um has been achieved at distance from focal plane about 10 Rayleigh lengths.. Both numerical simulations and experiment have been performed to demonstrate the ability of the method.
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    18. Tunable semiconductor laser based on interaction between strongly mismatched Fabry-Perot interferometer and waveguide modes

      Tunable semiconductor laser based on interaction between strongly mismatched Fabry-Perot interferometer and waveguide modes
      The method of spectral selection, based on small optical connection between tilted short Fabry-Perot interferometer and semiconductor optical amplifier has been proposed. It was shown, that short Fabry-Perot interferometer under certain inclination reflects back in narrowband lines, typical for transmitted spectrum. This effect has been used for creation swept semiconductor laser with wavelength tuning range 25 nm at central wavelength 1290 nm and coherence length 8 mm.
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    1-18 of 18
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    Tunable semiconductor laser based on interaction between strongly mismatched Fabry-Perot interferometer and waveguide modes Blind deconvolution algorithm for restoration OCT images with diffraction limited resolution Digital refocusing in optical coherence tomography Feature Of The Week 4/1/12: Russian Institute of Applied Physics Investigates Digital Refocusing in Optical Coherence Tomography Systems Noniterative method of reconstruction optical coherence tomography images with improved lateralresolution in semitransparent media Hybrid M-mode-like OCT imaging of 3D  microvasculature in vivo using reference-free  processing of complex-valued B-scans Multi-modal optical imaging characterization of atherosclerotic plaques Characterization of atherosclerotic plaques by cross-polarization optical coherence tomography Vessel-contrast enhancement in label-free optical coherence angiography based on phase and amplitude speckle variability Quantitative evaluation of atherosclerotic plaques using cross-polarization optical coherence tomography, nonlinear, and atomic force microscopy The impact of blood pressure variability on coronary arterial lumen dimensions as assessed by optical coherence tomography in patients with ST-elevation myocardial infarction Clinical diversity in macular corneal dystrophy: an optical coherence tomography study