1. Articles from Alexandr L. Matveyev

    1-8 of 8
    1. Multiparameter thermo-mechanical OCT-based characterization of laser-induced cornea reshaping

      Multiparameter thermo-mechanical OCT-based characterization of laser-induced cornea reshaping

      Phase-sensitive optical coherence tomography (OCT) is used for visualizing dynamic and cumulative strains and corneashape changes during laser-produced tissue heating. Such non-destructive (non-ablative) cornea reshaping can be used as a basis of emerging technologies of laser vision correction. In experiments with cartilaginous samples, polyacrilamide phantoms and excised rabbit eyes we demonstrate ability of the developed OCT system to simultaneously characterize transient and cumulated strain distributions, surface displacements, scattering tissue properties and possibility of temperature estimation via thermal-expansion measurements. The proposed approach can be implemented in perspective real-time OCT systems for ensuring safety of new methods of laser reshaping of cornea.

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    2. 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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    3. Deformation-induced speckle-pattern evolution and feasibility of correlational speckle tracking in optical coherence elastography

      Deformation-induced speckle-pattern evolution and feasibility of correlational speckle tracking in optical coherence elastography

      Feasibility of speckle tracking in optical coherence tomography (OCT) based on digital image correlation (DIC) is discussed in the context of elastography problems. Specifics of applying DIC methods to OCT, compared to processing of photographic images in mechanical engineering applications, are emphasized and main complications are pointed out. Analytical arguments are augmented by accurate numerical simulations of OCT speckle patterns. In contrast to DIC processing for displacement and strain estimation in photographic images, the accuracy of correlational speckle tracking in deformed OCT images is strongly affected by the coherent nature of speckles, for which strain-induced complications of speckle “blinking” and ...

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    4. 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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    5. 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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    6. Combining the correlation-stability approach to OCT elastography with the speckle-variance evaluation for quantifying the stiffness differences

      Combining the correlation-stability approach to OCT elastography with the speckle-variance evaluation for quantifying the stiffness differences

      We discuss an advanced variant of the correlation-stability (CS) approach to OCT elastography that is capable of quantifying the stiffness differences. The modified variant is based on natural combination of CS approach with the speckle-variance (SV) approach. It allows one to determine the strain dependence of the normalized speckle intensity variance function for two compared subsets taken from the OCT images corresponding to the initial and deformed states of the tissue. In previous studies we considered the basic dependence of the normalized speckle intensity variance function on the tissue strain under the assumption that the influence of translational displacements can ...

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    7. Towards free-hand implementation of OCT elastography: displacement-based approaches versus correlation-stability ones

      Towards free-hand implementation of OCT elastography: displacement-based approaches versus correlation-stability ones

      In this report, we present a comparative discussion of a recently proposed method of elastographic mapping based on comparison of correlation stability (CS) of different parts of sequentially obtained OCT images of the strained tissue and more conventional correlation approaches to elastographic mapping based on the initial reconstruction of the displacement field. The performed study is based on numerical simulations of speckle patterns generated by reproducing main features of image formation in real OCT scanners. Distortions of such speckle patterns caused by either translational motion of the studied sample or its straining are also incorporated in the developed simulation method ...

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    8. Elastographic mapping in optical coherence tomography using an unconventional approach based on correlation stability

      Elastographic mapping in optical coherence tomography using an unconventional approach based on correlation stability

      An approach to elastographic mapping in optical coherence tomography (OCT) using comparison of correlation stability of sequentially obtained intensity OCT images of the studied strained tissue is discussed. The basic idea is that for stiffer regions, the OCT image is distorted to a smaller degree. Consequently, cross-correlation maps obtained with compensation of trivial translational motion of the image parts using a sliding correlation window can represent the spatial distribution of the relative tissue stiffness. An important advantage of the proposed approach is that it allows one to avoid the stage of local-strain reconstruction via error-sensitive numerical differentiation of experimentally determined ...

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    1-8 of 8
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  2. Topics in the News

    1. (8 articles) Nizhny Novgorod State Medical Academy
    2. (8 articles) Grigory V. Gelikonov
    3. (7 articles) Institute of Applied Physics
    4. (7 articles) Valentin M. Gelikonov
    5. (5 articles) University of Toronto
    6. (5 articles) I. Alex Vitkin
    7. (1 articles) Ontario Cancer Institute
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    Elastographic mapping in optical coherence tomography using an unconventional approach based on correlation stability Towards free-hand implementation of OCT elastography: displacement-based approaches versus correlation-stability ones Combining the correlation-stability approach to OCT elastography with the speckle-variance evaluation for quantifying the stiffness differences Hybrid M-mode-like OCT imaging of 3D  microvasculature in vivo using reference-free  processing of complex-valued B-scans Scan-pattern and signal processing for microvasculature visualization with complex SD-OCT: tissue-motion artifacts robustness and decorrelation time - blood vessel characteristics Deformation-induced speckle-pattern evolution and feasibility of correlational speckle tracking in optical coherence elastography Vessel-contrast enhancement in label-free optical coherence angiography based on phase and amplitude speckle variability Multiparameter thermo-mechanical OCT-based characterization of laser-induced cornea reshaping Comparative study between intravitreal ranibizumab and triamcinolone treatment of diabetic macular edema as regard to optical coherence tomography changes and visual acuity What’s New in Optical Coherence Tomography Angiography for Glaucoma (Book Chapter) Looking into the Future: Optical Coherence Tomography for the Assessment of Cardiac Allograft Vasculopathy Effects of Age on Peripapillary and Macular Vessel Density Determined Using Optical Coherence Tomography Angiography in Healthy Eyes