1. Articles from Norman Lippok

    1-24 of 30 1 2 »
    1. RF properties of circular-ranging OCT signals

      RF properties of circular-ranging OCT signals

      Circular-ranging optical coherence tomography (CR–OCT) systems that use a time–stepped frequency comb source generate interference fringe signals that are more complex than those of a conventional swept–source OCT system. Here, we define a common terminology for describing these signals, and we develop a mathematical framework that relates the radio-frequency (RF) properties of these fringe signals to the parameters of the frequency comb source. With this framework, we highlight non-intuitive mechanisms whereby the design of the frequency comb source can affect imaging performance. We show, for example, that amplitude–pulsed time–stepped frequency comb sources have a sensitivity ...

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    2. Spectral- and Polarization-Dependent Scattering of Gold Nanobipyramids for Exogenous Contrast in Optical Coherence Tomography

      Spectral- and Polarization-Dependent Scattering of Gold Nanobipyramids for Exogenous Contrast in Optical Coherence Tomography

      Polarization-sensitive optical coherence tomography (PS-OCT) reveals the subsurface microstructure of biological tissue and provides information regarding the polarization state of light backscattered from tissue. Complementing OCT's structural signal with molecular imaging requires strategies to simultaneously detect multiple exogenous contrast agents with high specificity in tissue. Specific detection of molecular probes enables the parallel visualization of physiological, cellular, and molecular processes. Here we demonstrate that, by combining PS-OCT and spectral contrast (SC)-OCT measurements, we can distinguish signatures of different gold nanobipyramids (GNBPs) in lymphatic vessels from the surrounding tissue and blood vessels in live mouse models. This technique could ...

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    3. Multi-beam OCT imaging based on an integrated, free-space interferometer

      Multi-beam OCT imaging based on an integrated, free-space interferometer

      While it is a common practice to increase the speed of swept-source optical coherence tomography (OCT) systems by using a high-speed source, this approach may not always be optimal. Parallelization in the form of multiple imaging beams is an alternative approach, but scalable and low-loss multi-beam OCT architectures are needed to capitalize on its advantages. In this study, we demonstrate an eight-beam OCT system using an interferometer architecture comprising planar lightwave circuits (PLC) splitters, V-groove assemblies (VGA), and optical ribbon fibers. We achieved an excess loss and heterodyne efficiency on each channel that was close to that of single-beam systems ...

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    4. Resolving absolute depth in circular-ranging optical coherence tomography by using a degenerate frequency comb

      Resolving absolute depth in circular-ranging optical coherence tomography by using a degenerate frequency comb

      In Fourier-domain optical coherence tomography, an interference signal is generated that spans an RF bandwidth proportional to the product of three parameters: the imaging range, the imaging speed, and the inverse of the axial resolution. Circular-ranging optical coherence tomography (CR-OCT) architectures were introduced to ease long-range imaging by decoupling the imaging range from the signal RF bandwidth. As a consequence, present CR-OCT systems resolve the relative, but not the absolute, depth location of the scatterers. We introduce here a modified implementation of CR-OCT that uses a degenerate frequency comb source that allows recovery of absolute depth information while only minimally ...

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    5. Stable multi-megahertz circular-ranging optical coherence tomography at 1.3 µm

      Stable multi-megahertz circular-ranging optical coherence tomography at 1.3 µm

      In Fourier-domain optical coherence tomography (OCT), the finite bandwidth of the acquisition electronics constrains the depth range and speed of the system. Circular-ranging (CR) OCT methods use optical-domain compression to surpass this limit. However, the CR-OCT system architectures of prior reports were limited by poor stability and were confined to the 1.55 µm wavelength range. In this work, we describe a novel CR-OCT architecture that is free from these limitations. To ensure stable operation, temperature sensitive optical modules within the system were replaced; the kilometer-length fiber spools used in the stretched-pulse mode-locked (SPML) laser was eliminated in favor of ...

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    6. Intravascular Polarimetry in Patients With Coronary Artery Disease

      Intravascular Polarimetry in Patients With Coronary Artery Disease

      Objectives The aims of this first-in-human pilot study of intravascular polarimetry were to investigate polarization properties of coronary plaques in patients and to examine the relationship of these features with established structural characteristics available to conventional optical frequency domain imaging (OFDI) and with clinical presentation. Background Polarization-sensitive OFDI measures birefringence and depolarization of tissue together with conventional cross-sectional optical frequency domain images of subsurface microstructure. Methods Thirty patients undergoing polarization-sensitive OFDI (acute coronary syndrome, n = 12; stable angina pectoris, n = 18) participated in this study. Three hundred forty-two cross-sectional images evenly distributed along all imaged coronary arteries were classified into ...

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    7. Highly-stable, multi-megahertz circular-ranging optical coherence tomography at 1.3 µm based on a chirped fiber Bragg grating

      Highly-stable, multi-megahertz circular-ranging optical coherence tomography at 1.3 µm based on a chirped fiber Bragg grating

      In Fourier-domain optical coherence tomography (OCT), the finite bandwidth of the acquisition electronics constrains the depth range and speed of the system. Circular-ranging (CR) OCT methods use optical-domain compression to surpass this limit. However, the CR-OCT system architectures of prior reports were limited by poor stability and were confined to the 1.55 µm wavelength range. In this work, we describe a novel CR-OCT architecture that is free from these limitations. To ensure stable operation, temperature sensitive optical modules within the system were replaced; the kilometer-length fiber spools used in the stretched-pulse mode-locked (SPML) laser was eliminated in favor of ...

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    8. Extended Coherence Length and Depth Ranging Using a Fourier-Domain Mode-Locked Frequency Comb and Circular Interferometric Ranging

      Extended Coherence Length and Depth Ranging Using a Fourier-Domain Mode-Locked Frequency Comb and Circular Interferometric Ranging

      Fourier-domain mode locking has been a popular laser design for high-speed optical-frequency-domain imaging (OFDI), but achieving long coherence lengths, and therefore imaging range, has been challenging. The narrow linewidth of a Fourier-domain mode-locked (FDML) frequency-comb (FC) laser could provide an attractive platform for high-speed as well as long-range OFDI. Unfortunately, aliasing artifacts arising from signals beyond the principal measurement depth of the free spectral range have prohibited the use of an FDML FC laser for imaging so far. To make the increased coherence length of an FDML FC laser available, methods to manage such artifacts are required. Recently, coherent circular ...

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    9. Optic axis mapping with catheter-based polarization-sensitive optical coherence tomography

      Optic axis mapping with catheter-based polarization-sensitive optical coherence tomography

      Birefringence offers an intrinsic contrast mechanism related to the microstructure and arrangement of fibrillary tissue components. Here we present a reconstruction strategy to recover not only the scalar amount of birefringence, but also its optic axis orientation as a function of depth in tissue from measurements with catheter-based polarization-sensitive optical coherence tomography. A polarization symmetry constraint, intrinsic to imaging in the backscatter direction, facilitates the required compensation for wavelength-dependent transmission through the system elements, the rotating catheter, and overlying tissue layers. Applied to the intravascular imaging of coronary atherosclerosis in human patients, the optic axis affords refined interpretation of plaque ...

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    10. Extended coherence length and depth ranging using a Fourier domain mode-locked frequency comb and circular interferometric ranging

      Extended coherence length and depth ranging using a Fourier domain mode-locked frequency comb and circular interferometric ranging

      Fourier domain mode-locking (FDML) has been a popular laser design for high speed optical frequency domain imaging (OFDI) but achieving long coherence lengths, and therefore imaging range, has been challenging. The narrow instantaneous linewidth of a frequency comb (FC) FDML laser could provide an attractive platform for high speed as well as long range OFDI. Unfortunately, aliasing artifacts arising from signals beyond the principle measurement depth of the free spectral range have prohibited the use of a FC FDML for imaging so far. To make the enhanced coherence length of FC FDML laser available, methods to manage such artifacts are ...

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    11. Quantitative depolarization measurements for fiber‐based polarization‐sensitive optical frequency domain imaging of the retinal pigment epithelium

      Quantitative depolarization measurements for fiber‐based polarization‐sensitive optical frequency domain imaging of the retinal pigment epithelium

      A full quantitative evaluation of the depolarization of light may serve to assess concentrations of depolarizing particles in the retinal pigment epithelium and to investigate their role in retinal diseases in the human eye. Optical coherence tomography (OCT) and optical frequency domain imaging (OFDI) use spatial incoherent averaging to compute depolarization. Depolarization depends on accurate measurements of the polarization states at the receiver but also on the polarization state incident upon and within the tissue. Neglecting this dependence can result in artifacts and renders depolarization measurements vulnerable to birefringence in the system and in the sample. In this work, we ...

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    12. High-speed optical coherence tomography by circular interferometric ranging

      High-speed optical coherence tomography by circular interferometric ranging

      Existing three-dimensional optical imaging methods excel in controlled environments, but are difficult to deploy over large, irregular and dynamic fields. This means that they can be ill-suited for use in areas such as material inspection and medicine. To better address these applications, we developed methods in optical coherence tomography to efficiently interrogate sparse scattering fields, that is, those in which most locations (voxels) do not generate meaningful signal. Frequency comb sources are used to superimpose reflected signals from equispaced locations through optical subsampling. This results in circular ranging, and reduces the number of measurements required to interrogate large volumetric fields ...

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    13. Depolarization signatures map gold nanorods within biological tissue

      Depolarization signatures map gold nanorods within biological tissue

      Owing to their electromagnetic properties, tunability and biocompatibility, gold nanorods are being investigated as multifunctional probes for a range of biomedical applications. However, detection beyond the reach of traditional fluorescence and two-photon approaches and quantitation of their concentration in biological tissue remain challenging tasks in microscopy. Here, we show how the size and aspect ratio that impart gold nanorods with their plasmonic properties also make them a source of entropy. We report on how depolarization can be exploited as a strategy to visualize gold nanorod diffusion and distribution in biologically relevant scenarios ex vivo, in vitro and in vivo. We ...

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    14. Extended bandwidth wavelength swept laser source for high resolution optical frequency domain imaging

      Extended bandwidth wavelength swept laser source for high resolution optical frequency domain imaging

      Improving the axial resolution by providing wider bandwidth wavelength swept lasers remains an important issue for optical frequency domain imaging (OFDI). Here, we demonstrate a wide tuning range, all-fiber wavelength swept laser at a center wavelength of 1250 nm by combining two ring cavities that share a single Fabry-Perot tunable filter. The two cavities contain semiconductor optical amplifiers with central wavelengths of 1190 nm and 1292 nm, respectively. To avoid disturbing interference effects in the overlapping spectral region, we modulated the amplifiers in order to obtain consecutive wavelength sweeps in the two spectral regions. The two sweeps were fused together ...

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    15. 4D imaging of cardiac trabeculae contracting in vitro using gated OCT

      4D imaging of cardiac trabeculae contracting in vitro using gated OCT

      Cardiac trabeculae are widely used as experimental muscle preparations for studying heart muscle. However, their geometry (diameter, length, and shape) can vary not only amongst samples, but also within a sample, leading to inaccuracies in estimating their stress production, volumetric energy output, and/or oxygen consumption. Hence, it is desirable to have a system that can accurately image each trabecula in vitro during an experiment. To this end, we constructed an optical coherence tomography (OCT) system and implemented a gated imaging procedure to image actively contracting trabeculae and reconstruct their time-varying geometry. By imaging a single cross section while monitoring ...

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    16. Simple and versatile long range swept source for optical coherence tomography applications

      Simple and versatile long range swept source for optical coherence tomography applications

      We present a versatile long coherence length swept-source laser design for optical coherence tomography applications. This design consists of a polygonal spinning mirror and an optical gain chip in a modified Littman–Metcalf cavity. A narrowband intra-cavity filter is implemented through multiple passes off a diffraction grating set at grazing incidence. The key advantage of this design is that it can be readily adapted to any wavelength regions for which broadband gain chips are available. We demonstrate this by implementing sources at 1650 nm, 1550 nm, 1310 nm and 1050 nm. In particular, we present a 1310 nm swept source ...

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    17. Degree of polarization (uniformity) and depolarization index: unambiguous depolarization contrast for optical coherence tomography

      Degree of polarization (uniformity) and depolarization index: unambiguous depolarization contrast for optical coherence tomography

      The degree of polarization (uniformity) has attracted increased interest as a functional contrast in optical coherence tomography (OCT). However, its computation from a single polarization state suggests an ambiguity that is strongly dependent on a sample’s orientation. We here propose an improved metric to present depolarization with respect to the optical system rather than the propagating field. Using numerical simulations and optical frequency domain imaging, we evaluate the conventional DOP(U) for different polarization states and compare its performance with the unambiguous depolarization index.

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    18. Single input state, single-mode fiber-based polarization-sensitive optical frequency domain imaging by eigenpolarization referencing

      Single input state, single-mode fiber-based polarization-sensitive optical frequency domain imaging by eigenpolarization referencing

      Fiber-based polarization-sensitive optical frequency domain imaging is more challenging than free-space implementations. Using multiple input states, fiber-based systems provide sample birefringence information with the benefit of a flexible sample arm but come at the cost of increased system and acquisition complexity, and either reduce acquisition speed or require increased acquisition bandwidth. Here we show that with the calibration of a single polarization state, fiber-based configurations can approach the conceptual simplicity of traditional free-space configurations. We remotely control the polarization state of the light incident at the sample using the eigenpolarization states of a wave plate as a reference, and determine ...

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    19. Optical coherence tomography imaging of cardiac trabeculae

      Optical coherence tomography imaging of cardiac trabeculae

      An integrated instrument is being developed to study live cardiac trabeculae, which is capable of stimulating the muscle under controlled conditions while measuring the heat production, force, and sarcomere length distribution. To improve the accuracy of estimation of stress, strain, and volumetric heat production, the geometry of the muscle must be known. A spectral domain optical coherence tomography system (SD-OCT) has been constructed and calibrated to image the trabecula mounted inside the instrument. This system was mounted above the muscle chamber and a series of equally-spaced cross-sectional images were obtained. These were processed using a workflow developed to extract cross-sectional ...

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    20. Dispersion mapping at the micrometer scale using tri-band optical frequency domain imaging

      Dispersion mapping at the micrometer scale using tri-band optical frequency domain imaging

      Techniques to differentiate between materials are a powerful addition to the structural information traditionally available from optical coherence tomography images. We present label-free detection of water and lipid at a micrometer scale by evaluating their unique dispersion properties. Using a tri-band swept source configuration, we measure both β 2 and β 3 and show how to identify the two materials at sample thicknesses of 40 and 90 μm, respectively.

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    21. Dispersion mapping at the micron scale using tri-band optical frequency domain imaging

      Dispersion mapping at the micron scale using tri-band optical frequency domain imaging

      We present detection of water and lipid at a micron scale by evaluating their unique dispersion properties. Using a triband swept source configuration, we measure β2 and β3 and show how to identify the two materials at a sample thickness of 40μm and 90μm, respectively. This report reveals exciting new prospects for label free differentiation and segmentation using optical coherence tomography.

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    22. Single-shot speckle reduction and dispersion compensation in optical coherence tomography by compounding fractional Fourier domains

      Single-shot speckle reduction and dispersion compensation in optical coherence tomography by compounding fractional Fourier domains

      We present speckle suppression and dispersion compensation for Fourier-domain optical coherence tomography based on fractional Fourier transforms of a single A scan. A 1.54-fold reduction in speckle contrast was achieved with group velocity dispersion compensation. The method is demonstrated on biological samples using a swept source configuration at 1310 nm and a spectral-domain system at 840 nm

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    23. Dispersion compensation in Fourier domain optical coherence tomography using the fractional Fourier transform

      Dispersion compensation in Fourier domain optical coherence tomography using the fractional Fourier transform

      We address numerical dispersion compensation based on the use of the fractional Fourier transform (FrFT). The FrFT provides a new fundamental perspective on the nature and role of group-velocity dispersion in Fourier domain OCT. The dispersion induced by a 26 mm long water cell was compensated for a spectral bandwidth of 110 nm, allowing the theoretical axial resolution in air of 3.6 μm to be recovered from the dispersion degraded point spread function. Additionally, we present a new approach for depth dependent dispersion compensation based on numerical simulations. Finally, we show how the optimized fractional Fourier transform order parameter ...

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    1-24 of 30 1 2 »
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