1. 1-24 of 416 1 2 3 4 ... 16 17 18 »
    1. Eye-motion-corrected optical coherence tomography angiography using Lissajous scanning

      Eye-motion-corrected optical coherence tomography angiography using Lissajous scanning

      To correct eye motion artifacts in en face optical coherence tomography angiography (OCT-A) images, a Lissajous scanning method with subsequent software-based motion correction is proposed. The standard Lissajous scanning pattern is modified to be compatible with OCT-A and a corresponding motion correction algorithm is designed. The effectiveness of our method was demonstrated by comparing en face OCT-A images with and without motion correction. The method was further validated by comparing motion-corrected images with scanning laser ophthalmoscopy images, and the repeatability of the method was evaluated using a checkerboard image. A motion-corrected en face OCT-A image from a blinking case is ...

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    2. Virtual phase conjugation based optical tomography for single-shot three-dimensional imaging

      Virtual phase conjugation based optical tomography for single-shot three-dimensional imaging

      We propose a virtual phase conjugation (VPC) based optical tomography (VPC-OT) for realizing single-shot optical tomographic imaging systems. Using a computer-based numerical beam propagation, the VPC combines pre-modulation and post-demodulation of the probe beam’s wavefront, which provides an optical sectioning capability for resolving the depth coordinates. In VPC-OT, the physical optical microscope system and VPC are coupled using digital holography. Therefore, in contrast to conventional optical tomographic imaging (OTI) systems, this method does not require additional elements such as low-coherence light sources or confocal pinholes. It is challenging to obtain single-shot three-dimensional (3D) tomographic images using a conventional OTI ...

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    3. Large-volume, low-cost, high-precision FMCW tomography using stitched DFBs

      Large-volume, low-cost, high-precision FMCW tomography using stitched DFBs

      Optical frequency-modulated continuous-wave (FMCW) reflectometry is a ranging technique that allows for high-resolution distance measurements over long ranges. Similarly, swept-source optical coherence tomography (SS-OCT) provides high-resolution depth imaging over typically shorter distances and higher scan speeds. In this work, we demonstrate a low-cost, low-bandwidth 3D imaging system that provides the high axial resolution imaging capability normally associated with SS-OCT over typical FMCW ranging depths. The imaging system combines 12 distributed feedback laser (DFB) elements from a single butterfly module to provide an axial resolution of 27.1 μm over 6 m of depth and up to 14 cubic meters of ...

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    4. Shared-hole graph search with adaptive constraints for 3D optic nerve head optical coherence tomography image segmentation

      Shared-hole graph search with adaptive constraints for 3D optic nerve head optical coherence tomography image segmentation

      Optic nerve head (ONH) is a crucial region for glaucoma detection and tracking based on spectral domain optical coherence tomography (SD-OCT) images. In this region, the existence of a “hole” structure makes retinal layer segmentation and analysis very challenging. To improve retinal layer segmentation, we propose a 3D method for ONH centered SD-OCT image segmentation, which is based on a modified graph search algorithm with a shared-hole and locally adaptive constraints. With the proposed method, both the optic disc boundary and nine retinal surfaces can be accurately segmented in SD-OCT images. An overall mean unsigned border positioning error of 7 ...

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    5. Radiometric model for coaxial single- and multimode optical emission from double-clad fiber

      Radiometric model for coaxial single- and multimode optical emission from double-clad fiber

      Double-clad fibers (DCFs) are versatile waveguides supporting a single-mode core surrounded by a multimode inner cladding. DCFs are increasingly used for multimodal biomedical applications, such as imaging or therapy, for which the core is typically used for coherent illumination and the inner cladding, to support a concurrent modality. Proper optimization is, however, critical to ensure high optical performance and requires accurate modeling of coaxial single- and multimode output beams. In this paper, we present an approach based on geometrical optics and radiometry, which provides a simple and efficient modeling tool for designing and optimizing DCF-based systems. A radiometric definition of ...

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    6. Depth-resolved measurement of optical radiation-pressure forces with optical coherence tomography

      Depth-resolved measurement of optical radiation-pressure forces with optical coherence tomography

      A weakly focused laser beam can exert sufficient radiation pressure to manipulate microscopic particles over a large depth range. However, depth-resolved continuous measurement of radiation-pressure force profiles over an extended range about the focal plane has not been demonstrated despite decades of research on optical manipulation. Here, we present a method for continuous measurement of axial radiation-pressure forces from a weakly focused beam on polystyrene micro-beads suspended in viscous fluids over a depth range of 400 μm, based on real-time monitoring of particle dynamics using optical coherence tomography (OCT). Measurements of radiation-pressure forces as a function of beam power, wavelength ...

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    7. In vivo broadband visible light optical coherence tomography probe enables inverse spectroscopic analysis

      In vivo broadband visible light optical coherence tomography probe enables inverse spectroscopic analysis

      We report the design and characterization of a 6 mm outer diameter pull-back circumferential scanning visible optical coherence tomography probe. The probe’s large visible bandwidth (500–695 nm) allowed for inverse spectroscopic analysis and an axial resolution of ∼ 1.1    μm ∼1.1  μm in tissue. We verify spectral imaging capabilities by measuring microsphere backscattering spectra and demonstrate in vivo spatial nanoscale characterization of tissue.

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    8. Biomechanical assessment of myocardial infarction using optical coherence elastography

      Biomechanical assessment of myocardial infarction using optical coherence elastography

      Myocardial infarction (MI) leads to cardiomyocyte loss, impaired cardiac function, and heart failure. Molecular genetic analyses of myocardium in mouse models of ischemic heart disease have provided great insight into the mechanisms of heart regeneration, which is promising for novel therapies after MI. Although biomechanical factors are considered an important aspect in cardiomyocyte proliferation, there are limited methods for mechanical assessment of the heart in the mouse MI model. This prevents further understanding the role of tissue biomechanics in cardiac regeneration. Here we report optical coherence elastography (OCE) of the mouse heart after MI. Surgical ligation of the left anterior ...

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    9. Investigation of tissue cellularity at the tip of the core biopsy needle with optical coherence tomography

      Investigation of tissue cellularity at the tip of the core biopsy needle with optical coherence tomography

      We report the development and the pre-clinical testing of a new technology based on optical coherence tomography (OCT) for investigating tissue composition at the tip of the core biopsy needle. While ultrasound, computed tomography, and magnetic resonance imaging are routinely used to guide needle placement within a tumor, they still do not provide the resolution needed to investigate tissue cellularity (ratio between viable tumor and benign stroma) at the needle tip prior to taking a biopsy core. High resolution OCT imaging, however, can be used to investigate tissue morphology at the micron scale, and thus to determine if the biopsy ...

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    10. Real-time speckle reduction in optical coherence tomography using the dual window method

      Real-time speckle reduction in optical coherence tomography using the dual window method

      Speckle is an intrinsic noise of interferometric signals which reduces contrast and degrades the quality of optical coherence tomography (OCT) images. Here, we present a frequency compounding speckle reduction technique using the dual window (DW) method. Using the DW method, speckle noise is reduced without the need to acquire multiple frames. A ~25% improvement in the contrast-to-noise ratio (CNR) was achieved using the DW speckle reduction method with only minimal loss (~17%) in axial resolution. We also demonstrate that real-time speckle reduction can be achieved at a B-scan rate of ~21 frames per second using a graphic processing unit (GPU ...

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    11. Novel endoscope with increased depth of field for imaging human nasal tissue by microscopic optical coherence tomography

      Novel endoscope with increased depth of field for imaging human nasal tissue by microscopic optical coherence tomography

      Intravital microscopy (IVM) offers the opportunity to visualize static and dynamic changes of tissue on a cellular level. It is a valuable tool in research and may considerably improve clinical diagnosis. In contrast to confocal and non-linear microscopy, optical coherence tomography (OCT) with microscopic resolution (mOCT) provides intrinsically cross-sectional imaging. Changing focus position is not needed, which simplifies especially endoscopic imaging. For in-vivo imaging, here we are presenting endo-microscopic OCT (emOCT). A graded-index-lens (GRIN) based 2.75 mm outer diameter rigid endoscope is providing 1.5 – 2 µm nearly isotropic resolution over an extended field of depth. Spherical and chromatic ...

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    12. Swept source optical coherence tomography and tunable lens technology for comprehensive imaging and biometry of the whole eye

      Swept source optical coherence tomography and tunable lens technology for comprehensive imaging and biometry of the whole eye

      Standard optical systems in ophthalmology are strictly dedicated either to retinal or to anterior segment imaging due to the refractive properties of the eye. We demonstrate a swept source optical coherence tomography platform with an electrically tunable lens (ETL) for versatile 3D in vivo imaging of both the eye’s anterior segment and the retina. The optimized optical setup with adaptive operational states of the ETL permits focusing on the retina and on the anterior segment. Dynamic control of the optical beam focus allows for OCT image enhancement, leading to the visualization of the vitreous details at both the vitreo-lenticular ...

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    13. In vivo high resolution human corneal imaging using full-field optical coherence tomography

      In vivo high resolution human corneal imaging using full-field optical coherence tomography

      We present the first full-field optical coherence tomography (FFOCT) device capable of in vivo imaging of the human cornea. We obtained images of the epithelial structures, Bowman’s layer, sub-basal nerve plexus (SNP), anterior and posterior stromal keratocytes, stromal nerves, Descemet’s membrane and endothelial cells with visible nuclei. Images were acquired with a high lateral resolution of 1.7 µm and relatively large field-of-view of 1.26 mm x 1.26 mm – a combination, which, to the best of our knowledge, has not been possible with other in vivo human eye imaging methods. The latter together with a contactless ...

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    14. Cycloid scanning for wide field optical coherence tomography endomicroscopy and angiography in vivo

      Cycloid scanning for wide field optical coherence tomography endomicroscopy and angiography in vivo

      Devices that perform wide field-of-view (FOV) precision optical scanning are important for endoscopic assessment and diagnosis of luminal organ disease such as in gastroenterology. Optical scanning for in vivo endoscopic imaging has traditionally relied on one or more proximal mechanical actuators, limiting scan accuracy and imaging speed. There is a need for rapid and precise two-dimensional (2D) microscanning technologies to enable the translation of benchtop scanning microscopies to in vivo endoscopic imaging. We demonstrate a new cycloid scanner in a tethered capsule for ultrahigh speed, side-viewing optical coherence tomography (OCT) endomicroscopy in vivo . The cycloid capsule incorporates two scanners: a ...

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    15. Holographic line field en-face OCT with digital adaptive optics in the retina in vivo

      Holographic line field en-face OCT with digital adaptive optics in the retina in vivo

      We demonstrate a high-resolution line field en-face time domain optical coherence tomography (OCT) system using an off-axis holography configuration. Line field en-face OCT produces high speed en-face images at rates of up to 100 Hz. The high frame rate favors good phase stability across the lateral field-of-view which is indispensable for digital adaptive optics (DAO). Human retinal structures are acquired in-vivo with a broadband light source at 840 nm, and line rates of 10 kHz to 100 kHz. Structures of different retinal layers, such as photoreceptors, capillaries, and nerve fibers are visualized with high resolution of 2.8 µm and ...

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    16. Multiple aperture synthetic optical coherence tomography for biological tissue imaging

      Multiple aperture synthetic optical coherence tomography for biological tissue imaging

      An inherent compromise must be made between transverse resolution and depth of focus (DOF) in spectral domain optical coherence tomography (SD-OCT). Thus far, OCT has not been capable of providing a sufficient DOF to stably acquire cellular-resolution images. We previously reported a novel technique named multiple aperture synthesis (MAS) to extend the DOF in high-resolution OCT [Optica 4, 701 (2017)]. In this technique, the illumination beam is scanned across the objective lens pupil plane by being steered at the pinhole using a custom-made microcylindrical lens. Images captured via multiple distinctive apertures were digitally refocused, which is similar to synthetic aperture ...

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    17. Assessment of temporary cerebral effects induced by focused ultrasound with optical coherence tomography angiography

      Assessment of temporary cerebral effects induced by focused ultrasound with optical coherence tomography angiography

      Focused ultrasound (FUS) in combination with microbubbles temporally and locally increases the permeability of the blood-brain barrier (BBB) for facilitating drug delivery. However, the temporary effects of FUS on the brain microstructure and microcirculation need to be addressed. We used label-free optical coherence tomography (OCT) and OCT angiography (OCTA) to investigate the morphological and microcirculation changes in mouse brains due to FUS exposure at different power levels. Additionally, the recovery progress of the induced effects was studied. The results show that FUS exposure causes cerebral vessel dilation and can be identified and quantitatively analyzed via OCT/OCTA. Micro-hemorrhages can be ...

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    18. Complex differential variance angiography with noise-bias correction for optical coherence tomography of the retina

      Complex differential variance angiography with noise-bias correction for optical coherence tomography of the retina

      Complex differential variance (CDV) provides phase-sensitive angiographic imaging for optical coherence tomography (OCT) with immunity to phase-instabilities of the imaging system and small-scale axial bulk motion. However, like all angiographic methods, measurement noise can result in erroneous indications of blood flow that confuse the interpretation of angiographic images. In this paper, a modified CDV algorithm that corrects for this noise-bias is presented. This is achieved by normalizing the CDV signal by analytically derived upper and lower limits. The noise-bias corrected CDV algorithm was implemented into an experimental 1 μm wavelength OCT system for retinal imaging that used an eye tracking ...

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    19. Full ocular biometry through dual-depth whole-eye optical coherence tomography

      Full ocular biometry through dual-depth whole-eye optical coherence tomography

      We propose a new method of determining the optical axis (OA), pupillary axis (PA), and visual axis (VA) of the human eye by using dual-depth whole-eye optical coherence tomography (OCT). These axes, as well as the angles “α” between the OA and VA and “κ” between PA and VA, are important in many ophthalmologic applications, especially in refractive surgery. Whole-eye images are reconstructed based on simultaneously acquired images of the anterior segment and retina. The light from a light source is split into two orthogonal polarization components for imaging the anterior segment and retina, respectively. The OA and PA are identified based ...

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      Mentions: Korea University
    20. High-resolution retinal swept source optical coherence tomography with an ultra-wideband Fourier-domain mode-locked laser at MHz A-scan rates

      High-resolution retinal swept source optical coherence tomography with an ultra-wideband Fourier-domain mode-locked laser at MHz A-scan rates

      We present a new 1060 nm Fourier domain mode locked laser (FDML laser) with a record 143 nm sweep bandwidth at 2∙ 417 kHz = 834 kHz and 120 nm at 1.67 MHz, respectively. We show that not only the bandwidth alone, but also the shape of the spectrum is critical for the resulting axial resolution, because of the specific wavelength-dependent absorption of the vitreous. The theoretical limit of our setup lies at 5.9 µm axial resolution. In vivo MHz-OCT imaging of human retina is performed and the image quality is compared to the previous results acquired with 70 ...

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    21. Adaptive classifier allows enhanced flow contrast in OCT angiography using a histogram-based motion threshold and 3D Hessian analysis-based shape filtering

      Adaptive classifier allows enhanced flow contrast in OCT angiography using a histogram-based motion threshold and 3D Hessian analysis-based shape filtering

      In this Letter, we propose an adaptive digital classifier for flow contrast enhancement in optical coherence tomography angiography (OCTA). To solve the depth dependence in the initial motion-based classification, a depth-adaptive motion threshold was determined by performing a histogram analysis of an en-face image at each depth and identifying the static and dynamic voxel populations through fitting. In the follow-up shape-based classification, to adapt to the deformed vessel shapes in OCTA, a modified vesselness function along with an anisotropic Gaussian probe kernel was defined, and then a three-dimensional (3D) Hessian analysis-based shape filtering was utilized for effectively removing the residual ...

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    22. Broadband rotary joint for high-speed ultrahigh-resolution endoscopic OCT imaging at 800  nm

      Broadband rotary joint for high-speed ultrahigh-resolution endoscopic OCT imaging at 800  nm

      We report the development of a broadband rotary joint for high-speed ultrahigh-resolution endoscopic optical coherence tomography (OCT) imaging in the 800 nm spectral range. This rotary joint features a pair of achromatic doublets in order to achieve broadband operation for a 3 dB bandwidth over 150 nm. The measured one-way throughput of the rotary joint is greater than 80%, while the fluctuation of the double-pass coupling efficiency during 360 deg rotation is less than ± 5 % ±5% at a near video-rate speed of 20 revolutions/s (rps). The rotary joint is used in conjunction with a diffractive-optics-based endoscope and 800 nm ...

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    23. Visible Light Optical Coherence Microscopy of the Brain with Isotropic Femtoliter Resolution In Vivo

      Visible Light Optical Coherence Microscopy of the Brain with Isotropic Femtoliter Resolution In Vivo

      Most flying-spot Optical Coherence Tomography (OCT) and Optical Coherence Microscopy (OCM) systems use a symmetric confocal geometry, where the detection path retraces the illumination path starting from and ending with the spatial mode of a single mode optical fiber. Here, we describe a visible light OCM instrument that breaks this symmetry to improve transverse resolution without sacrificing collection efficiency. This was achieved by overfilling a water immersion objective on the illumination path, while maintaining a conventional Gaussian mode detection path (1/e2 intensity diameter ~0.82 Airy disks), enabling ~1.1 μm full-width at half-maximum (FWHM) transverse resolution. At the ...

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    24. Cross-correlation photothermal optical coherence tomography with high effective resolution

      Cross-correlation photothermal optical coherence tomography with high effective resolution

      We developed a cross-correlation photothermal optical coherence tomography (CC-PTOCT) system for photothermal imaging with high lateral and axial resolution. The CC-PTOCT system consists of a phase-sensitive OCT system, a modulated pumping laser, and a digital cross-correlator. The pumping laser was used to induce the photothermal effect in the sample, causing a slight phase modulation of the OCT signals. A spatial phase differentiation method was employed to reduce phase accumulation. The noise brought by the phase differentiation method and the strong background noise were suppressed efficiently by the cross-correlator, which was utilized to extract the photothermal signals from the modulated signals ...

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    1-24 of 416 1 2 3 4 ... 16 17 18 »
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