All Articles from Benjamin J. Vakoc -Optical Coherence Tomography News

Articles from Benjamin J. Vakoc

1-24 of 70 1 2 3 »
1. Using the dynamic forward scattering signal for optical coherence tomography based blood flow quantification
  
  Explore Optica Publishing Group Jun 15 2022 Ophthalmology
  
  To our knowledge, all existing optical coherence tomography approaches for quantifying blood flow, whether Doppler-based or decorrelation-based, analyze light that is back-scattered by moving red blood cells (RBCs). This work investigates the potential advantages of basing these measurements on light that is forward-scattered by RBCs, i.e., by looking at the signals back-scattered from below the vessel. We show experimentally that flowmetry based on forward-scattering is insensitive to vessel orientation for vessels that are approximately orthogonal to the imaging beam. We further provide proof-of-principle demonstrations of dynamic forward-scattering (DFS) flowmetry in human retinal and choroidal vessels.
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  Mentions: Massachusetts General Hospital Harvard University
2. RF properties of circular-ranging OCT signals
  
  Explore Optica Publishing Group Apr 4 2022 Tunable Sources
  
  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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  Mentions: Massachusetts General Hospital Harvard University
3. Relationship between axial resolution and signal-to-noise ratio in optical coherence tomography
  
  Explore Optica Publishing Group Mar 22 2022
  
  In optical coherence tomography (OCT), axial resolution and signal-to-noise ratio (SNR) are typically viewed as uncoupled parameters. We show that this is true only for mirror-like surfaces and that in diffuse scattering samples such as biological tissues there is an inherent coupling between axial resolution and measurement SNR. We explain the origin of this coupling and demonstrate that it can be used to achieve increased imaging penetration depth at the expense of resolution. Finally, we argue that this coupling should be considered during OCT system design processes that seek to balance the competing needs of resolution, sensitivity, and system/source ...
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  Mentions: Massachusetts Institute of Technology Massachusetts General Hospital Harvard University
4. Using the Dynamic Forward Scattering Signal for Optical Coherence Tomography based Blood Flow Quantification
  
  Explore bioRxiv.org Feb 4 2022 Ophthalmology
  
  To our knowledge, all existing optical coherence tomography approaches for quantifying blood flow, whether Doppler-based or decorrelation-based, analyze the light that is back-scattered by moving red blood cells (RBCs). This work investigates the potential advantages of basing these measurements of the light that is forward-scattered by RBCs, i.e., by looking at the signals back-scattered from below the vessel. We show experimentally that this results in a flowmetry measure that is insensitive to vessel orientation for vessels that are approximately orthogonal to the imaging beam. We further provide proof-of-principle demonstrations that DFS can be used to measure flow in human ...
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  Mentions: Massachusetts General Hospital Harvard University
5. THE RELATIONSHIP BETWEEN AXIAL RESOLUTION AND SIGNAL-TO-NOISE RATIO IN OPTICAL COHERENCE TOMOGRAPHY
  
  Explore arxiv.org Dec 29 2021
  
  In optical coherence tomography (OCT), axial resolution and signal-to-noise ratio (SNR) are typically viewed as uncoupled parameters. We show that this is only true for mirror-like surfaces, and that in diffuse scattering samples such as tissue there is an inherent coupling between axial resolution and measurement SNR. We explain the origin of this coupling and demonstrate that it can be used to achieve increased imaging penetration depth at the expense of resolution. Finally, we argue that this coupling should be considered during OCT system design processes that seek to balance competing needs of resolution, sensitivity, and system/source complexity.
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  Mentions: Massachusetts General Hospital Harvard University
6. Robust and easy-to-operate stretched-pulse mode-locked wavelength-swept laser with an all-polarization-maintaining fiber cavity for 10 MHz A-line rate optical coherence tomography
  
  Explore OSA | OSA Publishing Aug 4 2021 Tunable Sources
  
  We demonstrate robust and easy-to-operate stretched-pulse mode-locked laser (SPML) architectures using all-polarization-maintaining fiber laser cavities. Because of the polarization-maintaining construction, the laser performance is unaffected by mechanical perturbation on the cavity fibers. The lasers automatically initiate linear-in-wavenumber sweeps across 100 nm centered at 1290 nm with a 10 MHz repetition rate. OCT imaging with a sensitivity of 98 dB and a single-sided 6 dB coherence length of 2.5 mm is demonstrated. OCT angiography of a mouse brain that visualized three-dimensional cerebral microvasculature over a field of 1.5 m m × 1.5 m m 1.5mm×1.5mm (398 ...
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  Mentions: Massachusetts General Hospital Harvard University Korea Advanced Institute of Science and Technology
7. Multi-beam OCT imaging based on an integrated, free-space interferometer
  
  Explore OSA | OSA Publishing Feb 2 2021
  
  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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  Mentions: Massachusetts General Hospital Harvard University
8. Artifact Rates for 2D Retinal Nerve Fiber Layer Thickness Versus 3D Neuroretinal Rim Thickness Using Spectral-Domain Optical Coherence Tomography
  
  Explore TVST Journal Sep 26 2020 Ophthalmology
  
  Purpose : To compare the rates of clinically significant artifacts for two-dimensional peripapillary retinal nerve fiber layer (RNFL) thickness versus three-dimensional (3D) neuroretinal rim thickness using spectral-domain optical coherence tomography (SD-OCT). Methods : Only one eye per patient was used for analysis of 120 glaucoma patients and 114 normal patients. For RNFL scans and optic nerve scans, 15 artifact types were calculated per B-scan and per eye. Neuroretinal rim tissue was quantified by the minimum distance band (MDB). Global MDB neuroretinal rim thicknesses were calculated before and after manual deletion of B-scans with artifacts and subsequent automated interpolation. A clinically significant artifact ...
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  Mentions: Massachusetts General Hospital Harvard University Massachusetts Eye and Ear Infirmary
9. A Neural Network Approach to Quantify Blood Flow from Retinal OCT Intensity Time-Series Measurements
  
  Explore Nature Publishing Group Jun 17 2020 Ophthalmology
  
  Many diseases of the eye are associated with alterations in the retinal vasculature that are possibly preceded by undetected changes in blood flow. In this work, a robust blood flow quantification framework is presented based on optical coherence tomography (OCT) angiography imaging and deep learning. The analysis used a forward signal model to simulate OCT blood flow data for training of a neural network (NN). The NN was combined with pre- and post-processing steps to create an analysis framework for measuring flow rates from individual blood vessels. The framework’s accuracy was validated using both blood flow phantoms and human ...
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  Mentions: Massachusetts General Hospital Harvard University
10. Stepped frequency comb generation based on electro-optic phase-code mode-locking for moderate-speed circular-ranging OCT
  
  Explore OSA | OSA Publishing Jun 15 2020 Tunable Sources
  
  Circular-ranging (CR) optical coherence tomography (OCT) uses frequency comb sources to improve long-range imaging. While the initial development of CR-OCT focused on extremely high-speed imaging (i.e., operation at A-line rates of several to tens of MHz), there are many applications and imaging strategies for which more moderate speeds are preferred. However, we lack suitable frequency comb sources to enable moderate speed CR-OCT imaging. Here, we describe a novel phase-code mode-locking (PCML) laser architecture that can be operated from the kilohertz to megahertz range, while also offering novel features such as dynamic re-configurability and simplified linear-in-time frequency stepping. We demonstrate ...
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  Mentions: Massachusetts General Hospital Harvard University
11. 9.4 MHz A-line rate optical coherence tomography at 1300 nm using a wavelength-swept laser based on stretched-pulse active mode-locking
  
  Explore Nature Publishing Group Jun 11 2020 Tunable Sources
  
  In optical coherence tomography (OCT), high-speed systems based at 1300 nm are among the most broadly used. Here, we present 9.4 MHz A-line rate OCT system at 1300 nm. A wavelength-swept laser based on stretched-pulse active mode locking (SPML) provides a continuous and linear-in-wavenumber sweep from 1240 nm to 1340 nm, and the OCT system using this light source provides a sensitivity of 98 dB and a single-sided 6-dB roll-off depth of 2.5 mm. We present new capabilities of the 9.4 MHz SPML-OCT system in three microscopy applications. First, we demonstrate high quality OCTA imaging at a ...
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  Mentions: Massachusetts General Hospital Harvard University Korea Advanced Institute of Science and Technology
12. Artifact Rates for 2D Retinal Nerve Fiber Layer Thickness Versus 3D Retinal Nerve Fiber Layer Volume
  
  Explore TVST Journal Feb 16 2020 Ophthalmology
  
  Purpose : To compare artifact rates in two-dimensional (2D) versus three-dimensional (3D) retinal nerve fiber layer (RNFL) scans using Spectralis optical coherence tomography (OCT) Methods : Thirteen artifact types in 2D and 3D RNFL scans were identified in 106 glaucomatous eyes and 95 normal eyes. Artifact rates were calculated per B-scan and per eye. In 3D volume scans, artifacts were counted only for the 97 B-scans used to calculate RNFL parameters for the 2.5–3.5-mm annulus. 3D RNFL measurements were calculated twice, once before and again after deletion of B-scans with artifacts and subsequent automated interpolation. Results : For 2D scans ...
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  Mentions: Massachusetts General Hospital Harvard University Chang Gung University
13. Resolving absolute depth in circular-ranging optical coherence tomography by using a degenerate frequency comb
  
  Explore OSA | OSA Publishing Jan 12 2020 Tunable Sources
  
  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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  Mentions: Massachusetts General Hospital Harvard University
14. Stable multi-megahertz circular-ranging optical coherence tomography at 1.3 µm
  
  Explore OSA | OSA Publishing Dec 10 2019
  
  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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  Mentions: Massachusetts General Hospital Harvard University
15. Highly-stable, multi-megahertz circular-ranging optical coherence tomography at 1.3 µm based on a chirped fiber Bragg grating
  
  Explore arxiv.org Oct 26 2019 Tunable Sources
  
  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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  Mentions: Massachusetts General Hospital Harvard University
16. Diagnostic Capability of 3D Peripapillary Retinal Volume for Glaucoma Using Optical Coherence Tomography Customized Software
  
  Explore LWW Online Jun 25 2019 Ophthalmology
  
  Précis: The diagnostic capability of peripapillary retinal volume is similar to peripapillary retinal nerve fiber layer thickness for diagnosing glaucoma, but with fewer artifacts. Purpose: To compare the diagnostic capability of three-dimensional (3D) peripapillary retinal volume (RV) versus two-dimensional (2D) peripapillary retinal nerve fiber layer (RNFL) thickness for open-angle glaucoma . Patients and Methods: A retrospective cross-sectional analysis was conducted. A total of 180 subjects [113 open-angle glaucomas (OAG), 67 normal participants] had spectral domain optical coherence tomography (OCT) volume scans and RNFL thickness measurements. Peripapillary RV values were calculated using a custom-designed program with 4 circumpapillary annuli (CA): CA1 ...
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  Mentions: Massachusetts General Hospital University of Southern California Harvard University
17. Retinal Blood Vessel Caliber Estimation for Optical Coherence Tomography Angiography Images Based on 3D Superellipsoid Modeling
  
  Explore Home (World Scientific) May 14 2019 Ophthalmology
  
  Changes of retinal blood vessel calibers may reflect various retinal diseases and even several non-retinal diseases. We propose a new method to estimate retinal vessel calibers from 3D optical coherence tomography angiography (OCTA) images based on 3D modeling using superellipsoids. Taking advantage of 3D visualization of the retinal tissue microstructures in vivo provided by OCTA, our method can detect retinal blood vessels precisely, estimate their calibers reliably, and show the relative flow speed visually.
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  Mentions: Massachusetts General Hospital Harvard University Korea Advanced Institute of Science and Technology
18. Balloon catheter-based radiofrequency ablation monitoring in porcine esophagus using optical coherence tomography
  
  Explore OSA | OSA Publishing Apr 8 2019 Gastroenterology , Probes
  
  We present a microscopic image guidance platform for radiofrequency ablation (RFA) using a clinical balloon-catheter-based optical coherence tomography (OCT) system, currently used in the surveillance of Barrett’s esophagus patients. Our integrated thermal therapy delivery and monitoring platform consists of a flexible, customized bipolar RFA electrode array designed for use with a clinical balloon OCT catheter and a processing algorithm to accurately map the thermal coagulation process. Non-uniform rotation distortion was corrected using a feature tracking-based technique, which enables robust, frame-to-frame analysis of the temporal fluctuation of the complex OCT signal. With proper noise calibration, precise delineation of the thermal ...
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  Mentions: Massachusetts Institute of Technology Massachusetts General Hospital Harvard University
19. Toward optical coherence tomography angiography-based biomarkers to assess the safety of peripheral nerve electrostimulation
  
  Explore IOPscience Apr 2 2019 Neurology
  
  Objective: Peripheral nerves serve as a link between the central nervous system and its targets. Altering peripheral nerve activity through targeted electrical stimulation is being investigated as a therapy for modulating end organ function. To support rapid advancement in the field, novel approaches to predict and prevent nerve injury resulting from the electrical stimulation must be developed to overcome the limitations of traditional histological methods. The present study aims to develop an optical imaging-based approach for real-time assessment of peripheral nerve injury associated with electrical stimulation.  Approach: We developed an optical coherence tomography angiography system and a 3-D ...
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  Mentions: Massachusetts General Hospital Harvard University FDA
20. Extended Coherence Length and Depth Ranging Using a Fourier-Domain Mode-Locked Frequency Comb and Circular Interferometric Ranging
  
  Explore journals.aps.org Jan 10 2019 Tunable Sources
  
  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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  Mentions: Massachusetts Institute of Technology Massachusetts General Hospital Harvard University
21. Demonstration of Triband Multi-Focal Imaging with Optical Coherence Tomography
  
  Explore MDPI Open Access Journals Platform Dec 2 2018
  
  We demonstrate an extended depth of focus optical coherence tomography (OCT) system based on the use of chromatic aberration to create displaced focal planes in the sample. The system uses a wavelength-swept source tuning over three spectral bands and three separate interferometers, each of which interfaces to a single illumination/collection fiber. The resulting three imaged volumes are merged in post-processing to generate an image with a larger depth of focus than is obtained from each band individually. The improvements are demonstrated in structural imaging of a porous phantom and a lipid-cleared murine brain, and by angiographic imaging of human ...
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  Mentions: Massachusetts General Hospital Harvard University
22. Diagnostic Capability of Three-Dimensional Macular Parameters for Glaucoma Using Optical Coherence Tomography Volume Scans
  
  Explore IOVS Journal Oct 24 2018 Ophthalmology
  
  Purpose : To compare the diagnostic capability of three-dimensional (3D) macular parameters against traditional two-dimensional (2D) retinal nerve fiber layer (RNFL) thickness using spectral domain optical coherence tomography. To determine if manual correction and interpolation of B-scans improve the ability of 3D macular parameters to diagnose glaucoma. Methods : A total of 101 open angle glaucoma patients (29 with early glaucoma) and 57 healthy subjects had peripapillary 2D RNFL thickness and 3D macular volume scans. Four parameters were calculated for six different-sized annuli: total macular thickness (M-thickness), total macular volume (M-volume), ganglion cell complex (GCC) thickness, and GCC volume of the innermost ...
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  Mentions: Johns Hopkins University Massachusetts General Hospital Harvard University
23. Extended coherence length and depth ranging using a Fourier domain mode-locked frequency comb and circular interferometric ranging
  
  Explore arxiv.org Oct 24 2018 Tunable Sources
  
  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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  Mentions: Massachusetts Institute of Technology Massachusetts General Hospital Harvard University
24. Quantitative depolarization measurements for fiber‐based polarization‐sensitive optical frequency domain imaging of the retinal pigment epithelium
  
  Explore Wiley Online Library Jul 16 2018 Ophthalmology
  
  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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  Mentions: Massachusetts General Hospital Harvard University
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