1. Articles from opticsinfobase.org

  2. 1-24 of 1186 1 2 3 4 ... 48 49 50 »
    1. Anisotropic aberration correction using region of interest based digital adaptive optics in Fourier domain OCT

      Anisotropic aberration correction using region of interest based digital adaptive optics in Fourier domain OCT

      In this paper a numerical technique is presented to compensate for anisotropic optical aberrations, which are usually present across the lateral field of view in the out of focus regions, in high resolution optical coherence tomography and microscopy (OCT/OCM) setups. The recorded enface image field at different depths in the tomogram is digitally divided into smaller sub-regions or the regions of interest (ROIs), processed individually using subaperture based digital adaptive optics (DAO), and finally stitched together to yield a final image with a uniform diffraction limited resolution across the entire field of view (FOV). Using this method, a sub-micron ...

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    2. Analyzing three-dimensional ultrastructure of human cervical tissue using optical coherence tomography

      Analyzing three-dimensional ultrastructure of human cervical tissue using optical coherence tomography

      During pregnancy, the uterine cervix is the mechanical barrier that prevents delivery of a fetus. The underlying cervical collagen ultrastructure, which influences the overall mechanical properties of the cervix, plays a role in maintaining a successful pregnancy until term. Yet, not much is known about this collagen ultrastructure in pregnant and nonpregnant human tissue. We used optical coherence tomography to investigate the directionality and dispersion of collagen fiber bundles in the human cervix. An image analysis tool has been developed, combining a stitching method with a fiber orientation measurement, to study axially sliced cervix samples. This tool was used to ...

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    3. Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms

      Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms

      The fabrication of high-performance spherical gradient refractive index (S-GRIN) optics requires nondestructive metrology techniques to inspect the samples. We have developed an angular-scan, swept-source-based, Fourier-domain optical coherence tomography system centered at 1318 nm with 5 mm imaging depth capable of 180̊ polar scan and 360̊ azimuthal scan to investigate polymeric S-GRIN preforms. We demonstrate a method that enables simultaneous mapping of the group optical thickness, physical thickness, the radially-averaged group refractive index, and the transmitted wavefront of the S-GRIN preforms. The angular scan OCT imaging and metrology enables direct visualization, molding uniformity characterization, and optical property evaluations of the preforms ...

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    4. Compensation of spectral and RF errors in swept-source OCT for high extinction complex demodulation

      Compensation of spectral and RF errors in swept-source OCT for high extinction complex demodulation

      We provide a framework for compensating errors within passive optical quadrature demodulation circuits used in swept-source optical coherence tomography (OCT). Quadrature demodulation allows for detection of both the real and imaginary components of an interference fringe, and this information separates signals from positive and negative depth spaces. To achieve a high extinction (∼60 dB) between these positive and negative signals, the demodulation error must be less than 0.1% in amplitude and phase. It is difficult to construct a system that achieves this low error across the wide spectral and RF bandwidths of high-speed swept-source systems. In a prior work ...

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    5. Line-field parallel swept source MHz OCT for structural and functional retinal imaging

      Line-field parallel swept source MHz OCT for structural and functional retinal imaging

      We demonstrate three-dimensional structural and functional retinal imaging with line-field parallel swept source imaging (LPSI) at acquisition speeds of up to 1 MHz equivalent A-scan rate with sensitivity better than 93.5 dB at a central wavelength of 840 nm. The results demonstrate competitive sensitivity, speed, image contrast and penetration depth when compared to conventional point scanning OCT. LPSI allows high-speed retinal imaging of function and morphology with commercially available components. We further demonstrate a method that mitigates the effect of the lateral Gaussian intensity distribution across the line focus and demonstrate and discuss the feasibility of high-speed optical angiography ...

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    6. Depth-encoded synthetic aperture optical coherence tomography of biological tissues with extended focal depth

      Depth-encoded synthetic aperture optical coherence tomography of biological tissues with extended focal depth

      Optical coherence tomography (OCT) has proven to be able to provide three-dimensional (3D) volumetric images of scattering biological tissues for in vivo medical diagnostics. Unlike conventional optical microscopy, its depth-resolving ability (axial resolution) is exclusively determined by the laser source and therefore invariant over the full imaging depth. In contrast, its transverse resolution is determined by the objective’s numerical aperture and the wavelength which is only approximately maintained over twice the Rayleigh range. However, the prevailing laser sources for OCT allow image depths of more than 5 mm which is considerably longer than the Rayleigh range. This limits high ...

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    7. Polarization sensitive optical frequency domain imaging system for endobronchial imaging

      Polarization sensitive optical frequency domain imaging system for endobronchial imaging

      A polarization sensitive endoscopic optical frequency domain imaging (PS-OFDI) system with a motorized distal scanning catheter is demonstrated. It employs a passive polarization delay unit to multiplex two orthogonal probing polarization states in depth, and a polarization diverse detection unit to detect interference signal in two orthogonal polarization channels. Per depth location four electro-magnetic field components are measured that can be represented in a complex 2x2 field matrix. A Jones matrix of the sample is derived and the sample birefringence is extracted by eigenvalue decomposition. The condition of balanced detection and the polarization mode dispersion are quantified. A complex field ...

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    8. Spectral fractionation detection of gold nanorod contrast agents using optical coherence tomography

      Spectral fractionation detection of gold nanorod contrast agents using optical coherence tomography

      We demonstrate the proof of concept of a novel Fourier-domain optical coherence tomography contrast mechanism using gold nanorod contrast agents and a spectral fractionation processing technique. The methodology detects the spectral shift of the backscattered light from the nanorods by comparing the ratio between the short and long wavelength halves of the optical coherence tomography signal intensity. Spectral fractionation further divides the halves into sub-bands to improve spectral contrast and suppress speckle noise. Herein, we show that this technique can detect gold nanorods in intralipid tissue phantoms. Furthermore, cellular labeling by gold nanorods was demonstrated using retinal pigment epithelial cells ...

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    9. Developing cross-correlation as a method for microvessel imaging using clinical intravascular optical coherence tomography systems

      Developing cross-correlation as a method for microvessel imaging using clinical intravascular optical coherence tomography systems

      Current clinical intravascular optical coherence tomography (IV-OCT) imaging systems have limited in-vivo flow imaging capability because of non-uniform catheter rotation and inadequate A-line scan density. Thus any flow-localisation method that seeks to identify sites of variation within the OCT image data-sets, whether that is in amplitude or phase, produces non-representative correlation (or variance) maps. In this study, both mean and the variation within a set of cross-correlation maps, for static OCT imaging was used to differentiate flow from nonflow regions. Variation was quantified by use of standard deviation. The advantage of this approach is its ability to image flow, even ...

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    10. Simultaneous and localized measurement of diffusion and flow using optical coherence tomography

      Simultaneous and localized measurement of diffusion and flow using optical coherence tomography

      We report on the simultaneous and localized measurement of the diffusion coefficient and flow velocity based on the normalized autocorrelation function using optical coherence tomography (OCT). Our results on a flowing suspension of polystyrene spheres show that the flow velocity and the diffusion coefficient can be reliably estimated in a regime determined by the sample diffusivity, the local flow velocity, and the Gaussian beam waist. We experimentally demonstrate that a smaller beam waist results in an improvement of the velocity sensitivity at the expense of the precision and accuracy of the estimation of the diffusion coefficient. Further, we show that ...

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    11. High resolution Fourier domain optical coherence tomography in the 2 μm wavelength range using a broadband supercontinuum source

      High resolution Fourier domain optical coherence tomography in the 2 μm wavelength range using a broadband supercontinuum source

      A 220 nm bandwidth supercontinuum source in the two-micron wavelength range has been developed for use in a Fourier domain optical coherence tomography (FDOCT) system. This long wavelength source serves to enhance probing depth in highly scattering material with low water content. We present results confirming improved penetration depth in high opacity paint samples while achieving the high axial resolution needed to resolve individual paint layers. This is the first FDOCT developed in the 2 μm wavelength regime that allows fast, efficient capturing of 3D image cubes at a high axial resolution of 13 μm in air (or 9 μm ...

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    12. Full wave model of image formation in optical coherence tomography applicable to general samples

      Full wave model of image formation in optical coherence tomography applicable to general samples

      We demonstrate a highly realistic model of optical coherence tomography, based on an existing model of coherent optical microscopes, which employs a full wave description of light. A defining feature of the model is the decoupling of the key functions of an optical coherence tomography system: sample illumination, light-sample interaction and the collection of light scattered by the sample. We show how such a model can be implemented using the finite-difference time-domain method to model light propagation in general samples. The model employs vectorial focussing theory to represent the optical system and, thus, incorporates general illumination beam types and detection ...

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    13. High resolution Fourier domain optical coherence tomography in the 2 um wavelength range using a broadband supercontinuum source

      High resolution Fourier domain optical coherence tomography in the 2 um wavelength range using a broadband supercontinuum source

      A 220 nm bandwidth supercontinuum source in the two-micron wavelength range has been developed for use in a Fourier domain optical coherence tomography (FDOCT) system. This long wavelength source serves to enhance probing depth in highly scattering material with low water content. We present results confirming improved penetration depth in high opacity paint samples while achieving the high axial resolution needed to resolve individual paint layers. This is the first FDOCT developed in the 2 μm wavelength regime that allows fast, efficient capturing of 3D image cubes at a high axial resolution of 13 μm in air (or 9 μm ...

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    14. Background elimination and interferometric capability in optical coherence tomography by a nonlinear optical gating based on type-II second-harmonic generation

      Background elimination and interferometric capability in optical coherence tomography by a nonlinear optical gating based on type-II second-harmonic generation

      A novel method that uses nonlinear optical gating to control background illumination in optical coherence tomography is presented. With this method, the user can adjust the amount of undesired backscattering or eliminate it completely, which enables dark-field measurements. The interferometric capability of the method in a nonlinear optical regime is demonstrated with the coupling of three overlapping input waves to yield Fizeau fringes. The measurement of a 265 nm step is performed to validate this method, which was originally conceived for 3D MEMS characterization.

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    15. In vivo wide-field reflectance/fluorescence imaging and polarization-sensitive optical coherence tomography of human oral cavity with a forward-viewing probe

      In vivo wide-field reflectance/fluorescence imaging and polarization-sensitive optical coherence tomography of human oral cavity with a forward-viewing probe

      We report multimodal imaging of human oral cavity in vivo based on simultaneous wide-field reflectance/fluorescence imaging and polarization-sensitive optical coherence tomography (PS-OCT) with a forward-viewing imaging probe. Wide-field reflectance/fluorescence imaging and PS-OCT were to provide both morphological and fluorescence information on the surface, and structural and birefringent information below the surface respectively. The forward-viewing probe was designed to access the oral cavity through the mouth with dimensions of approximately 10 mm in diameter and 180 mm in length. The probe had field of view (FOV) of approximately 5.5 mm in diameter, and adjustable depth of field (DOF ...

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    16. In vivo imaging of human photoreceptor mosaic with wavefront sensorless adaptive optics optical coherence tomography

      In vivo imaging of human photoreceptor mosaic with wavefront sensorless adaptive optics optical coherence tomography

      Wavefront sensorless adaptive optics optical coherence tomography (WSAO-OCT) is a novel imaging technique for in vivo high-resolution depth-resolved imaging that mitigates some of the challenges encountered with the use of sensor-based adaptive optics designs. This technique replaces the Hartmann Shack wavefront sensor used to measure aberrations with a depth-resolved image-driven optimization algorithm, with the metric based on the OCT volumes acquired in real-time. The custom-built ultrahigh-speed GPU processing platform and fast modal optimization algorithm presented in this paper was essential in enabling real-time, in vivo imaging of human retinas with wavefront sensorless AO correction. WSAO-OCT is especially advantageous for developing ...

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    17. Measurements of the thermal coefficient of optical attenuation at different depth regions of in vivo human skins using optical coherence tomography: a pilot study

      Measurements of the thermal coefficient of optical attenuation at different depth regions of in vivo human skins using optical coherence tomography: a pilot study

      We present detailed measurement results of optical attenuation’s thermal coefficients (referenced to the temperature of the skin surface) in different depth regions of in vivo human forearm skins using optical coherence tomography (OCT). We first design a temperature control module with an integrated optical probe to precisely control the surface temperature of a section of human skin. We propose a method of using the correlation map to identify regions in the skin having strong correlations with the surface temperature of the skin and find that the attenuation coefficient in these regions closely follows the variation of the surface temperature ...

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    18. Evaluation of microsurgical tasks with OCT-guided and/or robot-assisted ophthalmic forceps

      Evaluation of microsurgical tasks with OCT-guided and/or robot-assisted ophthalmic forceps

      Real-time intraocular optical coherence tomography (OCT) visualization of tissues with surgical feedback can enhance retinal surgery. An intraocular 23-gauge B-mode forward-imaging co-planar OCT-forceps, coupling connectors and algorithms were developed to form a unique ophthalmic surgical robotic system. Approach to the surface of a phantom or goat retina by a manual or robotic-controlled forceps, with and without real-time OCT guidance, was performed. Efficiency of lifting phantom membranes was examined. Placing the co-planar OCT imaging probe internal to the surgical tool reduced instrument shadowing and permitted constant tracking. Robotic assistance together with real-time OCT feedback improved depth perception accuracy. The first-generation integrated ...

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    19. Fiber-based polarization-sensitive OCT for birefringence imaging of the anterior eye segment

      Fiber-based polarization-sensitive OCT for birefringence imaging of the anterior eye segment

      We demonstrate a prototype system of polarization-sensitive optical coherence tomography (PS-OCT) designed for clinical studies of the anterior eye segment imaging. The system can measure Jones matrices of the sample with depth-multiplexing of two orthogonal incident polarizations and polarization-sensitive detection. An optical clock is generated using a quadrature modulator and a logical circuit to double the clock frequency. Systematic artifacts in measured Jones matrices are theoretically analyzed and numerically compensated using signals at the surface of the sample. Local retardation images of filtering blebs after trabeculectomy show improved visualization of subconjunctival tissue, sclera, and scar tissue of the bleb wall ...

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    20. Developmental and morphological studies in Japanese medaka with ultra-high resolution optical coherence tomography

      Developmental and morphological studies in Japanese medaka with ultra-high resolution optical coherence tomography

      We propose ultra-high resolution optical coherence tomography to study the morphological development of internal organs in medaka fish in the post-embryonic stages at micrometer resolution. Different stages of Japanese medaka were imaged after hatching in vivo with an axial resolution of 2.8 µm in tissue. Various morphological structures and organs identified in the OCT images were then compared with the histology. Due to the medaka’s close resemblance to vertebrates, including humans, these morphological features play an important role in morphogenesis and can be used to study diseases that also occur in humans.

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      Mentions: Barry Cense
    21. Towards model-based adaptive optics optical coherence tomography

      Towards model-based adaptive optics optical coherence tomography

      The transfer function for optical wavefront aberrations in single-mode fiber based optical coherence tomography is determined. The loss in measured OCT signal due to optical wavefront aberrations is quantified using Fresnel propagation and the calculation of overlap integrals. A distinction is made between a model for a mirror and a scattering medium model. The model predictions are validated with measurements on a mirror and a scattering medium obtained with an adaptive optics optical coherence tomography setup. Furthermore, a one-step defocus correction, based on a single A-scan measurement, is derived from the model and verified. Finally, the pseudo-convex structure of the ...

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    22. Analysis of multimode fiber bundles for endoscopic spectral-domain optical coherence tomography

      Analysis of multimode fiber bundles for endoscopic spectral-domain optical coherence tomography

      A theoretical analysis of the use of a fiber bundle in spectral-domain optical coherence tomography (OCT) systems is presented. The fiber bundle enables a flexible endoscopic design and provides fast, parallelized acquisition of the OCT data. However, the multimode characteristic of the fibers in the fiber bundle affects the depth sensitivity of the imaging system. A description of light interference in a multimode fiber is presented along with numerical simulations and experimental studies to illustrate the theoretical analysis.

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    23. Microscopic OCT imaging with focus extension by ultrahigh-speed acousto-optic tunable lens and stroboscopic illumination

      Microscopic OCT imaging with focus extension by ultrahigh-speed acousto-optic tunable lens and stroboscopic illumination

      We develop high-resolution optical coherence tomography (OCT) system with high-speed acousto-optic tunable lens. Stroboscopic pulsed illumination is used for the first time to perform time-resolved OCT imaging with acousto-optic tunable focusing. The operation of ultrahigh-speed tunable acousto-optic lens is demonstrated theoretically and experimentally. Focal position tuning at MHz frequency range is experimentally shown in the imaging system leading to OCT images with extended depth of focus. Imaging with active optical elements is helpful for improvement of photon collection efficiency, depth of focus and enhancement of the image quality.

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    24. Optically buffered Jones-matrix-based multifunctional optical coherence tomography with polarization mode dispersion correction

      Optically buffered Jones-matrix-based multifunctional optical coherence tomography with polarization mode dispersion correction

      Polarization mode dispersion (PMD) degrades the performance of Jones-matrix-based polarization-sensitive multifunctional optical coherence tomography (JM-OCT). The problem is specially acute for optically buffered JM-OCT, because the long fiber in the optical buffering module induces a large amount of PMD. This paper aims at presenting a method to correct the effect of PMD in JM-OCT. We first mathematically model the PMD in JM-OCT and then derive a method to correct the PMD. This method is a combination of simple hardware modification and subsequent software correction. The hardware modification is introduction of two polarizers which transform the PMD into global complex modulation ...

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    1-24 of 1186 1 2 3 4 ... 48 49 50 »
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