1. 1-24 of 994 1 2 3 4 ... 40 41 42 »
    1. Volumetric directional optical coherence tomography

      Volumetric directional optical coherence tomography

      Photoreceptor loss and resultant thinning of the outer nuclear layer (ONL) is an important pathological feature of retinal degenerations and may serve as a useful imaging biomarker for age-related macular degeneration. However, the demarcation between the ONL and the adjacent Henle’s fiber layer (HFL) is difficult to visualize with standard optical coherence tomography (OCT). A dedicated OCT system that can precisely control and continuously and synchronously update the imaging beam entry points during scanning has not been realized yet. In this paper, we introduce a novel imaging technology, Volumetric Directional OCT (VD-OCT), which can dynamically adjust the incident beam ...

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    2. Balanced detection spectral-domain optical coherence tomography with a single line-scan camera

      Balanced detection spectral-domain optical coherence tomography with a single line-scan camera

      This paper describes a balanced detection spectral-domain optical coherence tomography (BD-SD-OCT) system for suppressing autocorrelation (AC) artifacts and increasing the signal-to-noise ratio (SNR). The system employed three optical fiber couplers to generate two phase-opposed interference spectra that were acquired by a single line-scan camera simultaneously. When compared with conventional unbalanced detection SD-OCT systems, the developed BD-SD-OCT system improved the SNR by 5.4-6 dB and suppressed the AC term by 5-10 dB. The imaging quality of the BD-SD-OCT system was evaluated by in vivo imaging of human nail folds and retinas.

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    3. Optical design, optimization and validation of an extended-depth-of-field optical coherence tomography probe based on mirror-tunneling

      Optical design, optimization and validation of an extended-depth-of-field optical coherence tomography probe based on mirror-tunneling

      We present results from optimizing mirror-tunnel based optical coherence tomography probes, achieving extended depth of field at high resolution. We achieved 6 µm spot diameter over 1 mm depth in simulations and validated experimentally.

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    4. Optimized number of the primary singular values for image reconstruction in reflection matrix based optical coherence tomography

      Optimized number of the primary singular values for image reconstruction in reflection matrix based optical coherence tomography

      A reflection matrix based optical coherence tomography (OCT) is recently proposed and expected to extend the imaging-depth limit twice. However, the imaging depth and hence the image quality heavily depend on the number of primary singular values considered for image reconstruction. To this regard, we propose a method based on correlation between image pairs reconstructed from different number of singular values and corresponding remainders. The obtained correlation curve and another feature curve fetched from the former are then fed to a long short-term memory (LSTM) network classifier to identify the optimized number of primary singular values for image reconstruction. Simulated ...

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    5. Globally optimal OCT surface segmentation using a constrained IPM optimization

      Globally optimal OCT surface segmentation using a constrained IPM optimization

      Segmentation of multiple surfaces in optical coherence tomography (OCT) images is a challenging problem, further complicated by the frequent presence of weak boundaries, varying layer thicknesses, and mutual influence between adjacent surfaces. The traditional graph-based optimal surface segmentation method has proven its effectiveness with its ability to capture various surface priors in a uniform graph model. However, its efficacy heavily relies on handcrafted features that are used to define the surface cost for the “goodness” of a surface. Recently, deep learning (DL) is emerging as a powerful tool for medical image segmentation thanks to its superior feature learning capability. Unfortunately ...

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    6. Pulsatile tissue deformation dynamics of the murine retina and choroid mapped by 4D optical coherence tomography

      Pulsatile tissue deformation dynamics of the murine retina and choroid mapped by 4D optical coherence tomography

      Irregular ocular pulsatility and altered mechanical tissue properties are associated with some of the most sight-threatening eye diseases. Here we present 4D optical coherence tomography (OCT) for the quantitative assessment and depth-resolved mapping of pulsatile dynamics in the murine retina and choroid. Through a pixel-wise analysis of phase changes of the complex OCT signal, we reveal spatiotemporal displacement characteristics across repeated frame acquisitions. We demonstrate in vivo fundus elastography (FUEL) imaging in wildtype mouse retinas and in a mouse model of retinal neovascularization and uncover subtle structural deformations related to ocular pulsation. Our data in mouse eyes hold promise for ...

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    7. Interferometric imaging of thermal expansion for temperature control in retinal laser therapy

      Interferometric imaging of thermal expansion for temperature control in retinal laser therapy

      Precise control of the temperature rise is a prerequisite for proper photothermal therapy. In retinal laser therapy, the heat deposition is primarily governed by the melanin concentration, which can significantly vary across the retina and from patient to patient. In this work, we present a method for determining the optical and thermal properties of layered materials, directly applicable to the retina, using low-energy laser heating and phase-resolved optical coherence tomography (pOCT). The method is demonstrated on a polymer-based tissue phantom heated with a laser pulse focused onto an absorbing layer buried below the phantom’s surface. Using a line-scan spectral-domain ...

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    8. Continuous spectral zooming for in vivo live 4D-OCT with MHz A-scan rates and long coherence

      Continuous spectral zooming for in vivo live 4D-OCT with MHz A-scan rates and long coherence

      We present continuous three-dimensional spectral zooming in live 4D-OCT using a home-built FDML based OCT system with 3.28 MHz A-scan rate. Improved coherence characteristics of the FDML laser allow for imaging ranges up to 10 cm. For the axial spectral zoom feature, we switch between high resolution and long imaging range by adjusting the sweep range of our laser. We present a new imaging setup allowing for synchronized adjustments of the imaging range and lateral field of view during live OCT imaging. For this, a novel inline recalibration algorithm was implemented that enables numerical k-linearization of the raw OCT ...

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    9. Multi-task learning approach for volumetric segmentation and reconstruction in 3D OCT images

      Multi-task learning approach for volumetric segmentation and reconstruction in 3D OCT images

      The choroid is the vascular layer of the eye that supplies photoreceptors with oxygen. Changes in the choroid are associated with many pathologies including myopia where the choroid progressively thins due to axial elongation. To quantize these changes, there is a need to automatically and accurately segment the choroidal layer from optical coherence tomography (OCT) images. In this paper, we propose a multi-task learning approach to segment the choroid from three-dimensional OCT images. Our proposed architecture aggregates the spatial context from adjacent cross-sectional slices to reconstruct the central slice. Spatial context learned by this reconstruction mechanism is then fused with ...

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    10. Investigation of multiple scattering in space and spatial-frequency domains: with application to the analysis of aberration-diverse optical coherence tomography

      Investigation of multiple scattering in space and spatial-frequency domains: with application to the analysis of aberration-diverse optical coherence tomography

      Optical microscopy suffers from multiple scattering (MS), which limits the optical imaging depth into scattering media. We previously demonstrated aberration-diverse optical coherence tomography (AD-OCT) for MS suppression, based on the principle that for datasets acquired with different aberration states of the imaging beam, MS backgrounds become decorrelated while single scattering (SS) signals remain correlated, so that a simple coherent average can be used to enhance the SS signal over the MS background. Here, we propose a space/spatial-frequency domain analysis framework for the investigation of MS in OCT, and apply the framework to compare AD-OCT (using astigmatic beams) to standard ...

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    11. Stent detection with very thick tissue coverage in intravascular OCT

      Stent detection with very thick tissue coverage in intravascular OCT

      Coronary stenting or percutaneous coronary intervention (PCI) is widely used to treat coronary artery disease. Improper deployment of stents may lead to post-PCI complication, in-stent restenosis, stent fracture and stent thrombosis. Intravascular optical coherence tomography (OCT) with micron-scale resolution provides accurate in vivo assessment of stent apposition/malapposition and neointima coverage. However, manual stent analysis is labor intensive and time consuming. Existing automated methods with intravascular OCT mainly focused on stent struts with thin tissue coverage. We developed a deep learning method to automatically analyze stents with both thin (≤0.3mm) and very thick tissue coverage (>0.3mm), and an ...

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    12. Extraction of phase-based optoretinograms (ORG) from serial B-scans acquired over tens of seconds by mouse retinal raster scanning OCT system

      Extraction of phase-based optoretinograms (ORG) from serial B-scans acquired over tens of seconds by mouse retinal raster scanning OCT system

      Several specialized retinal optical coherence tomography (OCT) acquisition and processing methods have been recently developed to allow in vivo probing of light-evoked photoreceptors function, focusing on measurements in individual photoreceptors (rods and cones). Recent OCT investigations in humans and experimental animals have shown that the outer segments in dark-adapted rods and cones elongate in response to the visible optical stimuli that bleach fractions of their visual photopigment. We have previously successfully contributed to these developments by implementing OCT intensity-based "optoretinograms" (ORG), the paradigm of using near-infrared OCT (NIR OCT) to measure bleaching-induced back-scattering and/or elongation changes of photoreceptors in ...

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    13. Deep convolutional neural network-based scatterer density and resolution estimators in optical coherence tomography

      Deep convolutional neural network-based scatterer density and resolution estimators in optical coherence tomography

      We present deep convolutional neural network (DCNN)-based estimators of the tissue scatterer density (SD), lateral and axial resolutions, signal-to-noise ratio (SNR), and effective number of scatterers (ENS, the number of scatterers within a resolution volume). The estimators analyze the speckle pattern of an optical coherence tomography (OCT) image in estimating these parameters. The DCNN is trained by a large number (1,280,000) of image patches that are fully numerically generated in OCT imaging simulation. Numerical and experimental validations were performed. The numerical validation shows good estimation accuracy as the root mean square errors were 0.23%, 3.65 ...

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    14. Optical coherence tomography-guided confocal Raman microspectroscopy for rapid measurements in tissues

      Optical coherence tomography-guided confocal Raman microspectroscopy for rapid measurements in tissues

      We report a joint system with both confocal Raman spectroscopy (CRS) and optical coherence tomography (OCT) modules capable of quickly addressing the region of interest in a tissue for targeted Raman measurements from OCT. By using an electrically tunable lens in the Raman module, the focus of the module can be adjusted to address any specific depth indicated in an OCT image in a few milliseconds. We demonstrate the performance of the joint system in the depth dependent measurements of an ex vivo swine tissue and in vivo human skin. This system can be useful in measuring samples embedded with ...

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    15. Dynamic wavefront distortion in resonant scanners

      Dynamic wavefront distortion in resonant scanners

      Dynamic mirror deformation can substantially degrade the performance of optical instruments using resonant scanners. Here, we evaluate two scanners with resonant frequencies > 12 k H z >12kHz with low dynamic distortion. First, we tested an existing galvanometric motor with a novel, to the best of our knowledge, mirror substrate material, silicon carbide, which resonates at 13.8 kHz. This material is stiffer than conventional optical glasses and has lower manufacturing toxicity than beryllium, the stiffest material currently used for this application. Then, we tested a biaxial microelectromechanical (MEMS) scanner with the resonant axis operating at 29.4 kHz. Dynamic deformation ...

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    16. Proactive spectrometer matching for excess noise suppression in balanced visible light optical coherence tomography (OCT)

      Proactive spectrometer matching for excess noise suppression in balanced visible light optical coherence tomography (OCT)

      Supercontinuum sources for visible light spectral domain OCT (SDOCT) are noisy and often expensive. Balanced detection can reduce excess noise, but is rarely used in SDOCT. Here, we show that balanced detection can achieve effective excess noise cancellation across all depths if two linear array spectrometers are spectrally well-matched. We propose excess noise correlation matrices as tools to achieve such precise spectral matching. Using optomechanical adjustments, while monitoring noise correlations, we proactively match wavelength sampling of two different spectrometers to just a few picometers in wavelength, or 0.001% of the overall spectral range. We show that proactively-matched spectrometers can ...

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    17. Single-cell all-optical coherence elastography with optical tweezers

      Single-cell all-optical coherence elastography with optical tweezers

      The elastic properties of cells are important for many of their functions, however the development of label free noninvasive cellular elastography method is a challenging topic. We present a novel single-cell all-optical coherence elastography method that combines optical tweezers producing mechanical excitation on the cell membrane or organelle and phase-sensitive optical coherence microscopy measuring sample response and determining its mechanical properties. The method allows living cells imaging with a lateral resolution of 0.5 μm and an axial resolution up to 10 nm, making it possible to detect nanometer displacements of the cell organelles and to record the propagation of ...

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    18. Reducing speckle in anterior segment optical coherence tomography images based on a convolutional neural network

      Reducing speckle in anterior segment optical coherence tomography images based on a convolutional neural network

      Speckle noise is ubiquitous in the optical coherence tomography (OCT) image of the anterior segment, which greatly affects the image quality and destroys the relevant structural information. In order to reduce the influence of speckle noise in OCT images, a denoising algorithm based on a convolutional neural network is proposed in this paper. Unlike traditional algorithms that directly obtain denoised images, the algorithm model proposed in this paper learns the speckle noise distribution through the constructed trainable OCT dataset and indirectly obtains the denoised result image. In order to verify the performance of the model, we compare the denoising results ...

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    19. Combined anterior segment OCT and wavefront-based autorefractor using a shared beam

      Combined anterior segment OCT and wavefront-based autorefractor using a shared beam

      We have combined an anterior segment (AS) optical coherence tomography (OCT) system and a wavefront-based aberrometer with an approach that senses ocular wavefront aberrations using the OCT beam. Temporal interlacing of the OCT and aberrometer channels allows for OCT images and refractive error measurements to be acquired continuously and in real-time. The system measures refractive error with accuracy and precision comparable to that of clinical autorefractors. The proposed approach provides a compact modular design that is suitable for integrating OCT and wavefront-based autorefraction within the optical head of the ophthalmic surgical microscope for guiding cataract surgery or table-top devices for ...

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    20. Investigation of methods to extract confocal function parameters for the depth resolved determination of attenuation coefficients using OCT in intralipid samples, titanium oxide phantoms, and in vivo human retinas

      Investigation of methods to extract confocal function parameters for the depth resolved determination of attenuation coefficients using OCT in intralipid samples, titanium oxide phantoms, and in vivo human retinas

      The attenuation coefficient provides a quantitative parameter for tissue characterization and can be calculated from optical coherence tomography (OCT) data, but accurate determination requires compensation for the confocal function. We present extensive measurement series for extraction of the focal plane and the apparent Rayleigh length from the ratios of OCT images acquired with different focus depths and compare these results with two alternative approaches. By acquiring OCT images for a range of different focus depths the optimal focus plane difference is determined for intralipid and titanium oxide (TiO 2 ) phantoms with different scatterer concentrations, which allows for calculation of the ...

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    21. Deep imaging with 1.3 µm dual-axis optical coherence tomography and an enhanced depth of focus

      Deep imaging with 1.3 µm dual-axis optical coherence tomography and an enhanced depth of focus

      For many clinical applications, such as dermatology, optical coherence tomography (OCT) suffers from limited penetration depth due primarily to the highly scattering nature of biological tissues. Here, we present a novel implementation of dual-axis optical coherence tomography (DA-OCT) that offers improved depth penetration in skin imaging at 1.3 µm compared to conventional OCT. Several unique aspects of DA-OCT are examined here, including the requirements for scattering properties to realize the improvement and the limited depth of focus (DOF) inherent to the technique. To overcome this limitation, our approach uses a tunable lens to coordinate focal plane selection with image ...

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    22. Simulating scan formation in multimodal optical coherence tomography: angular-spectrum formulation based on ballistic scattering of arbitrary-form beams

      Simulating scan formation in multimodal optical coherence tomography: angular-spectrum formulation based on ballistic scattering of arbitrary-form beams

      We present a computationally highly efficient full-wave spectral model of OCT-scan formation with the following features: allowance of arbitrary phase-amplitude profile of illuminating beams; absence of paraxial approximation; utilization of broadly used approximation of ballistic scattering by discrete scatterers without limitations on their density/location and scattering strength. The model can easily incorporate the wave decay, dispersion, measurement noises with given signal-to-noise ratios and arbitrary inter-scan displacements of scatterers. We illustrate several of such abilities, including comparative simulations of OCT-scans for Bessel versus Gaussian beams, presence of arbitrary aberrations at the tissue boundary and various scatterer motions. The model flexibility ...

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    23. Fast and accurate spectral-estimation axial super-resolution optical coherence tomography

      Fast and accurate spectral-estimation axial super-resolution optical coherence tomography

      Spectral-estimation OCT (SE-OCT) is a computational method to enhance the axial resolution beyond the traditional bandwidth limit. However, it has not yet been used widely due to its high computational load, dependency on user-optimized parameters, and inaccuracy in intensity reconstruction. In this study, we implement SE-OCT using a fast implementation of the iterative adaptive approach (IAA). This non-parametric spectral estimation method is optimized for use on OCT data. Both in simulations and experiments we show an axial resolution improvement with a factor between 2 and 10 compared to standard discrete Fourier transform. Contrary to parametric methods, IAA gives consistent peak ...

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    24. 105° field of view non-contact handheld swept-source optical coherence tomography

      105° field of view non-contact handheld swept-source optical coherence tomography

      We demonstrate a handheld swept-source optical coherence tomography (OCT) system with a 400 kHz vertical-cavity surface-emitting laser (VCSEL) light source, a non-contact approach, and an unprecedented single shot 105° field of view (FOV). We also implemented a spiral scanning pattern allowing real-time visualization with improved scanning efficiency. To the best of our knowledge, this is the widest FOV achieved in a portable non-contact OCT retinal imaging system to date. Improvements to the FOV may aid the evaluation of retinal diseases such as retinopathy of prematurity, where important vitreoretinal changes often occur in the peripheral retina.

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    1-24 of 994 1 2 3 4 ... 40 41 42 »
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