1. Articles from Kostadinka Bizheva

    1-24 of 41 1 2 »
    1. 250 kHz, 1.5 µm resolution SD-OCT for in-vivo cellular imaging of the human cornea

      250 kHz, 1.5 µm resolution SD-OCT for in-vivo cellular imaging of the human cornea

      We present the first spectral domain optical coherence tomography (SD-OCT) system that combines an isotropic imaging resolution of ~1.5 µm in biological tissue with a 250 kHz image acquisition rate, for in vivo non-contact, volumetric imaging of the cellular structure of the human cornea. OCT images of the healthy human cornea acquired with this system reveal the cellular structure of the corneal epithelium, cellular debris and mucin clusters in the tear film, the shape, size and spatial distribution of the sub-basal corneal nerves and keratocytes in the corneal stroma, as well as reflections from endothelial nuclei. The corneal images ...

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    2. Dense concentric circle scanning protocol for measuring pulsatile retinal blood flow in rats with Doppler optical coherence tomography

      Dense concentric circle scanning protocol for measuring pulsatile retinal blood flow in rats with Doppler optical coherence tomography

      The variability in the spatial orientation of retinal blood vessels near the optic nerve head (ONH) results in imprecision of the measured Doppler angle and therefore the pulsatile blood flow (BF), when those parameters are evaluated using Doppler OCT imaging protocols based on dual-concentric circular scans. Here, we utilized a dense concentric circle scanning protocol and evaluated its precision for measuring pulsatile retinal BF in rats for different numbers of the circular scans. An spectral domain optical coherence tomography (SD-OCT) system operating in the 1060-nm spectral range with image acquisition rate of 47,000 A-scans/s was used to acquire ...

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    3. In-vivo imaging of the palisades of Vogt and the limbal crypts with sub-micrometer axial resolution optical coherence tomography

      In-vivo imaging of the palisades of Vogt and the limbal crypts with sub-micrometer axial resolution optical coherence tomography

      A research-grade OCT system was used to image in-vivo and without contact with the tissue, the cellular structure and microvasculature of the healthy human corneo-scleral limbus. The OCT system provided 0.95 µm axial and 4 µm (2 µm) lateral resolution in biological tissue depending on the magnification of the imaging objective. Cross-sectional OCT images acquired tangentially from the inferior limbus showed reflective, loop-like features that correspond to the fibrous folds of the palisades of Vogt (POV). The high OCT resolution allowed for visualization of individual cells inside the limbal crypts, capillaries extending from the inside of the POV’s ...

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    4. Relationship between vessel diameter and depth measurements within the limbus using ultra-high resolution optical coherence tomography

      Relationship between vessel diameter and depth measurements within the limbus using ultra-high resolution optical coherence tomography

      To establish a relationship between the diameter and depth position of vessels in the superior and inferior corneo-scleral limbus using ultra-high resolution optical coherence tomography (UHR-OCT). Methods Volumetric OCT images of the superior and inferior limbus were acquired from 14 healthy subjects with a research-grade UHR-OCT system. Differences in vessel diameter and depth between superior and inferior limbus were analyzed using repeated measured ANOVA in SPSS and R. Results The mean (± SD) superior and inferior diameters were 29 ± 18 μm and 24 ± 18 μm respectively, and the mean (± SD) superior and inferior depths were 177 ± 109 μm and 207 ± 132 ...

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    5. Sub-micrometer axial resolution OCT for in-vivo imaging of the cellular structure of healthy and keratoconic human corneas

      Sub-micrometer axial resolution OCT for in-vivo imaging of the cellular structure of healthy and keratoconic human corneas

      Corneal degenerative conditions such as keratoconus (KC) cause progressive damage to the anterior corneal tissue and eventually severely compromise visual acuity. The ability to visualize corneal tissue damage in-vivo at cellular or sub-cellular level at different stages of development of KC and other corneal diseases, can aid the early diagnostics as well as the development of more effective treatment approaches for various corneal pathologies, including keratoconus. Here, we present the optical design of an optical coherence tomography system that can achieve 0.95 µm axial resolution in biological tissue and provide test results for the system’s spatial resolution and ...

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    6. Analysis of scattering statistics and governing distribution functions in optical coherence tomography

      Analysis of scattering statistics and governing distribution functions in optical coherence tomography

      The probability density function (PDF) of light scattering intensity can be used to characterize the scattering medium. We have recently shown that in optical coherence tomography (OCT), a PDF formalism can be sensitive to the number of scatterers in the probed scattering volume and can be represented by the K-distribution, a functional descriptor for non-Gaussian scattering statistics. Expanding on this initial finding, here we examine polystyrene microsphere phantoms with different sphere sizes and concentrations, and also human skin and fingernail in vivo . It is demonstrated that the K-distribution offers an accurate representation for the measured OCT PDFs. The behavior of ...

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    7. Probability density function formalism for optical coherence tomography signal analysis

      Probability density function formalism for optical coherence tomography signal analysis

      The distribution of backscattered intensities as described by the probability density function (PDF) of tissue-scattered light contains information that may be useful for tissue assessment and diagnosis, including characterization of its pathology. In this Letter, we examine the PDF description of the light scattering statistics in a well characterized tissue-like particulate medium using optical coherence tomography (OCT). It is shown that for low scatterer density, the governing statistics depart considerably from a Gaussian description and follow the K distribution for both OCT amplitude and intensity. The PDF formalism is shown to be independent of the scatterer flow conditions; this is ...

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    8. In Vivo Imaging and Morphometry of the Human Pre-Descemet's Layer and Endothelium With Ultrahigh-Resolution Optical Coherence Tomography

      In Vivo Imaging and Morphometry of the Human Pre-Descemet's Layer and Endothelium With Ultrahigh-Resolution Optical Coherence Tomography

      Purpose : To visualize in vivo and quantify the thickness of the posterior corneal layers: the acellular pre-Descemet's layer (PDL), Descemet's membrane (DM), and endothelium (END) in healthy subjects, using ultrahigh-resolution optical coherence tomography (UHR-OCT). Methods : A research-grade, 800-nm UHR-OCT system with 0.95-μm axial resolution in corneal tissue was used to image in vivo the posterior cornea in healthy subjects. The system offers approximately 98 dB sensitivity for 680 μW optical power incident on the cornea and 34,000 A-scans/s image acquisition rate. This study comprised 20 healthy subjects, aged 20 to 60 years. The thickness ...

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    9. Quantitative assessment of oral microstructural and microvascular changes in late oral radiation toxicity, using noninvasive in-vivo optical coherence tomography

      Quantitative assessment of oral microstructural and microvascular changes in late oral radiation toxicity, using noninvasive in-vivo optical coherence tomography

      Background and objectives: About half of the head and neck cancer patients treated with radiotherapy suffer from late radiation effects months to years after the treatment. The most common diagnosis and monitoring methods for such oral toxicities are based on surface examination of the oral tissue, which is subjective. Therefore, subsurface imaging and image quantification tools can be highly useful for monitoring these late effects as these approaches are more robust and objective. In this study, we demonstrate the ability of optical coherence tomography (OCT) technology and its newly developed quantitative imaging platform to reveal subsurface microstructural and microvascular changes ...

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    10. Depth Compensated Spectral Domain Optical Coherence Tomography via Digital Compensation

      Depth Compensated Spectral Domain Optical Coherence Tomography via Digital Compensation

      Spectral Domain Optical Coherence Tomography (SD-OCT) is a well-known imaging modality which allows for \textit{in-vivo} visualization of the morphology of different biological tissues at cellular level resolutions. The overall SD-OCT imaging quality in terms of axial resolution and Signal-to-Noise Ratio (SNR) degrades with imaging depth, while the lateral resolution degrades with distance from the focal plane. This image quality degradation is due both to the design of the SD-OCT imaging system and the optical properties of the imaged object. Here, we present a novel Depth Compensated SD-OCT (DC-OCT) system that integrates a Depth Compensating Digital Signal Processing (DC-DSP) module ...

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    11. Axial resolution improvement in spectral domain optical coherence tomography using a depth-adaptive maximum-a-posterior framework

      Axial resolution improvement in spectral domain optical coherence tomography using a depth-adaptive maximum-a-posterior framework

      The axial resolution of Spectral Domain Optical Coherence Tomography (SD-OCT) images degrades with scanning depth due to the limited number of pixels and the pixel size of the camera, any aberrations in the spectrometer optics and wavelength dependent scattering and absorption in the imaged object [1]. Here we propose a novel algorithm which compensates for the blurring effect of these factors of the depth-dependent axial Point Spread Function (PSF) in SDOCT images. The proposed method is based on a Maximum A Posteriori (MAP) reconstruction framework which takes advantage of a Stochastic Fully Connected Conditional Random Field (SFCRF) model. The aim ...

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    12. Noise-compensated Homotopic Non-local Regularized Reconstruction for Rapid Retinal Optical Coherence Tomography Image Acquisitions

      Noise-compensated Homotopic Non-local Regularized Reconstruction for Rapid Retinal Optical Coherence Tomography Image Acquisitions

      Background Optical coherence tomography (OCT) is a minimally invasive imaging technique, which utilizes the spatial and temporal coherence properties of optical waves backscattered from biological material. Recent advances in tunable lasers and infrared camera technologies have enabled an increase in the OCT imaging speed by a factor of more than 100, which is important for retinal imaging where we wish to study fast physiological processes in the biological tissue. However, the high scanning rate causes proportional decrease of the detector exposure time, resulting in a reduction of the system signal-to-noise ratio (SNR). One approach to improving the image quality of ...

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    13. Automatic tracking of pupillary dynamics from in vivo functional optical coherence tomography images

      Automatic tracking of pupillary dynamics from in vivo functional optical coherence tomography images

      A major challenge currently faced in measuring visually evoked optical changes in different retinal layers using in vivo and non-invasive functional optical coherence tomography (fOCT) is the need for pupillary dilation drugs to enable reliable measurement of the retinal functional responses. However, there are situations where the use of pupillary dilation drugs is not suitable in both clinical and animal ophthalmic research situations. To overcome this challenge, we propose a new approach to tracking visually evoked pupillary dynamics, based on the use of a fast scanning fOCT system and a novel computerised framework, which can then be used to isolate ...

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    14. Stochastic speckle noise compensation in optical coherence tomography using non-stationary spline-based speckle noise modelling

      Stochastic speckle noise compensation in optical coherence tomography using non-stationary spline-based speckle noise modelling

      Optical coherence tomography (OCT) allows for non-invasive 3D visualization of biological tissue at cellular level resolution. Often hindered by speckle noise, the visualization of important biological tissue details in OCT that can aid disease diagnosis can be improved by speckle noise compensation. A challenge with handling speckle noise is its inherent non-stationary nature, where the underlying noise characteristics vary with the spatial location. In this study, an innovative speckle noise compensation method is presented for handling the non-stationary traits of speckle noise in OCT imagery. The proposed approach centers on a non-stationary spline-based speckle noise modeling strategy to characterize the ...

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    15. Optical coherence tomography platform for microvascular imaging and quantification: initial experience in late oral radiation toxicity patients

      Optical coherence tomography platform for microvascular imaging and quantification: initial experience in late oral radiation toxicity patients

      An optical coherence tomography (OCT) microvascular imaging platform, consisting of Doppler (DOCT) and speckle variance (svOCT) modalities, and microvascular image quantification tools are developed. The quantification methods extract blood flow-related parameters from DOCT images and vessel morphological parameters from svOCT images. This platform is used to assess the microvascular (DOCT and svOCT) images obtained during a clinical study on late oral radiation toxicity. This specific pathology was considered a suitable scenario for verifying the performance of the developed quantification platform because late oral radiation toxicity is known to involve microvascular damage. The derived parameters are compared between several DOCT and ...

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    16. Development of quantitative parameters to assess in-vivo optical coherence tomography images of late oral radiation toxicity patients

      Development of quantitative parameters to assess in-vivo optical coherence tomography images of late oral radiation toxicity patients

      Late oral radiation toxicity is a common condition occurring in a considerable percentage of head and neck cancer patients after radiation therapy which reduces their quality of life. The current examination of these patients is based on a visual inspection of the surface of the oral cavity; however, it is well known that many of the complications start in the subsurface layers before any superficial manifestation. Considering the currently suboptimal examination techniques, we address this clinical problem by using optical coherence tomography (OCT) to monitor the subsurface oral layers with micron-scale resolution images. A spectral-domain OCT system and a specialized ...

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    17. Noninvasive imaging of the early effect of sodium iodate toxicity in a rat model of outer retina degeneration with spectral domain optical coherence tomography

      Noninvasive imaging of the early effect of sodium iodate toxicity in a rat model of outer retina degeneration with spectral domain optical coherence tomography

      An ultrahigh resolution spectral domain optical coherence tomography (SD-OCT) system is used to observe for the first time in vivo the early effect of sodium iodate ( NaIO 3 ) toxicity on retinal morphology. Retinal degeneration is induced in rats via tail vein injection of NaIO 3 and structural changes in the outer retina are assessed longitudinally at baseline and 1, 2, 3, 6, 8, and 10 h, and 12 post drug administration with OCT, H&E histology, and IgG immunochemistry. Disruption of the structural integrity and changes in the optical reflectivity of the photoreceptor inner (IS) and outer segment (OS) layers ...

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    18. Energy-guided learning approach to compressive FD-OCT

      Energy-guided learning approach to compressive FD-OCT

      High quality, large size volumetric imaging of biological tissue with optical coherence tomography (OCT) requires large number and high density of scans, which results in large data acquisition volume. This may lead to corruption of the data with motion artifacts related to natural motion of biological tissue, and could potentially cause conflicts with the maximum permissible exposure of biological tissue to optical radiation. Therefore, OCT can benefit greatly from different approaches to sparse or compressive sampling of the data where the signal is recovered from its sub-Nyquist measurements. In this paper, a new energy-guided compressive sensing approach is proposed for ...

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    19. Stimulus-Specific Pupil Dynamics Measured in Birds (Gallus gallus domesticus) In Vivo with Ultrahigh Resolution Optical Coherence Tomography

      Stimulus-Specific Pupil Dynamics Measured in Birds (Gallus gallus domesticus) In Vivo with Ultrahigh Resolution Optical Coherence Tomography
      Purpose. To demonstrate the ability of high speed, ultrahigh-resolution optical coherence tomography (UHR-OCT) to measure and characterize in vivo visual stimulus-specific pupil dynamics in birds. Methods. Ten two-week old White Leghorn ( Gallus gallus domesticus ) chickens were imaged in this study. The chickens were dark-adapted for 1 hour and anesthetized with 2% isoflurane prior to the imaging procedure. Blue, green, and red single flash visual stimuli of 7 ms duration were used to evoke pupillary responses. UHR-OCT cross-sectional images of the pupil were acquired prior, during, and for several seconds after the visual stimuli onset. Images were processed with a novel ...
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    20. Stimulus Specific Pupil Dynamics Measured in Birds (Gallus Gallus Domesticus) in vivo with Ultrahigh Resolution Optical Coherence Tomography

      Stimulus Specific Pupil Dynamics Measured in Birds (Gallus Gallus Domesticus) in vivo with Ultrahigh Resolution Optical Coherence Tomography

      Purpose:To demonstrate the ability of high speed, ultra-high resolution optical coherence tomography (UHR-OCT) to measure and characterize in vivo visual stimulus specific pupil dynamics in birds. Methods:Ten two-week old White Leghorn (Gallus gallus domesticus) chickens were imaged in this study. The chickens were dark adapted for one hour and anesthetized with 2% isoflurane prior to the imaging procedure. Blue, green, and red single flash visual stimuli of 7ms duration were used to evoke pupillary responses. UHR-OCT cross-sectional images of the pupil were acquired prior, during and for several seconds after the visual stimuli onset. Images were processed with ...

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    21. Homotopic, non-local sparse reconstruction of optical coherence tomography imagery

      Homotopic, non-local sparse reconstruction of optical coherence tomography imagery

      The resolution in optical coherence tomography imaging is an important parameter which determines the size of the smallest features that can be visualized. Sparse sampling approaches have shown considerable promise in producing high resolution OCT images with fewer camera pixels, reducing both the cost and the complexity of an imaging system. In this paper, we propose a non-local approach to the reconstruction of high resolution OCT images from sparsely sampled measurements. An iterative strategy is introduced for minimizing a homotopic, non-local regularized functional in the spatial domain, subject to data fidelity constraints in the k-space domain. The novel algorithm was ...

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    22. Optimal signal processing of nonlinearity in swept-source and spectral-domain optical coherence tomography

      Optimal signal processing of nonlinearity in swept-source and spectral-domain optical coherence tomography

      We demonstrate the efficiency of the convolution using an optimized Kaiser–Bessel window to resample nonlinear data in wavenumber for Fourier-domain optical coherence tomography (OCT). We extend our previous experimental demonstration that was performed with a specific swept-source nonlinearity. The method is now applied to swept-source OCT data obtained for various simulated swept-source nonlinearities as well as spectral-domain OCT data obtained from both simulations and experiments. Results show that the new optimized method is the most efficient for handling all the different types of nonlinearities in the wavenumber domain that one can encounter in normal practice. The efficiency of the ...

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    23. Noninvasive in vivo structural and vascular imaging of human oral tissues with spectral domain optical coherence tomography

      Noninvasive in vivo structural and vascular imaging of human oral tissues with spectral domain optical coherence tomography

      A spectral domain optical coherence tomography (SD-OCT) system and an oral imaging probe have been developed to visualize the microstructural morphology and microvasculature in the human oral cavity. Structural OCT images of ex vivo pig oral tissues with the histology of the same sites were acquired and compared for correlations. Structural in vivo OCT images of healthy human tissue as well as a pathologic site (ulcer) were obtained and analyzed based on the results of the ex vivo pig study, drawing on the similarity between human and swine oral tissues. In vivo Doppler and speckle variance OCT images of the ...

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    24. Correlation of visually evoked intrinsic optical signals and electroretinograms recorded from chicken retina with a combined functional optical coherence tomography and electroretinography system

      Correlation of visually evoked intrinsic optical signals and electroretinograms recorded from chicken retina with a combined functional optical coherence tomography and electroretinography system

      Visually evoked fast intrinsic optical signals (IOSs) were recorded for the first time in vivo from all layers of healthy chicken retina by using a combined functional optical coherence tomography (fOCT) and electroretinography (ERG) system. The fast IOSs were observed to develop within ∼ 5  ms from the on-set of the visual stimulus, whereas slow IOSs were measured up to 1 s later. The visually evoked IOSs and ERG traces were recorded simultaneously, and a clear correlation was observed between them. The ability to measure visually evoked fast IOSs non-invasively and in vivo from individual retinal layers could significantly improve the ...

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    1-24 of 41 1 2 »
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for in-vivo imaging of human and rodent retina in the 1060nm wavelength range General Bayesian estimation for speckle noise reduction in optical coherence tomography retinal imagery Swelling of the Human Cornea Revealed by High Speed, Ultrahigh Resolution Optical Coherence Tomography Combined optical coherence tomography and electroretinography system for in vivo simultaneous morphological and functional imaging of the rodent retina In vivo volumetric imaging of the human upper eyelid with ultrahigh-resolution optical coherence tomography Postdoctoral or Research Scientist Position in Biomedical Optics at Baylor College of Medicine Investigation of cell dynamics in 3D cell spheroids and cell interaction with 3D printed scaffolds by mOCT Neoatherosclerosis ― Long-Term Assessment of Bioresorbable Vascular Scaffold ― Intravascular Polarimetry for Tissue Characterization of Coronary Atherosclerosis Efficacy and Reproducibility of Attenuation-Compensated Optical Coherence Tomography for Assessing External Elastic Membrane Border and Plaque Composition in Native and Stented Segments ― An In Vivo and Histology-Based Study ― Spectral domain - Optical coherence tomography (SD-OCT) as a monitoring tool for alterations in mouse lenses