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

Articles from Benjamin J. Vakoc

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1. 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: Brett E. Bouma Massachusetts General Hospital Harvard University
2. 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 Benjamin J. Vakoc
3. 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 Wang Yuhl Oh
4. 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: Brett E. Bouma Johannes F. de Boer Massachusetts General Hospital
5. 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 Benjamin J. Vakoc
6. 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: Brett E. Bouma Massachusetts General Hospital Harvard University
7. 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: Brett E. Bouma Massachusetts General Hospital Harvard University
8. 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: Brett E. Bouma Johannes F. de Boer Massachusetts General Hospital
9. 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 Wang Yuhl Oh
10. 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: Brett E. Bouma Massachusetts Institute of Technology Massachusetts General Hospital
11. 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 Daniel X. Hammer Harvard University
12. 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: Brett E. Bouma Massachusetts Institute of Technology Massachusetts General Hospital
13. 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: Brett E. Bouma Massachusetts General Hospital Harvard University
14. 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: Brett E. Bouma Johannes F. de Boer Johns Hopkins University
15. 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: Brett E. Bouma Massachusetts Institute of Technology Massachusetts General Hospital
16. 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: Brett E. Bouma Massachusetts General Hospital Harvard University
17. Optical coherence tomography angiography based biomarkers to assess the safety of peripheral nerve electrostimulation
  
  Explore SPIE Digital Library Mar 20 2018
  
  Peripheral nerves connect and relay information between the central nervous system and its target organs. Small arteries traverse the epineurium and are responsible for supplying blood to the axons and cells within the nerves. Constriction or damage to these vessels can reduce perfusion leading to ischemic insults. Peripheral nerve electrostimulation has been approved for the treatment of epilepsy, depression and migraines, and is also being studied for the treatment of rheumatoid arthritis, Crohn’s disease, polycystic ovary syndrome, and type II diabetes. While the safety and efficacy of currently approved medical devices is well established, next generation devices may require ...
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  Mentions: Massachusetts General Hospital Daniel X. Hammer Harvard University
18. High-speed optical coherence tomography by circular interferometric ranging
  
  Explore Nature Publishing Group Feb 1 2018
  
  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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  Mentions: Massachusetts General Hospital Harvard University Benjamin J. Vakoc
19. Complex differential variance angiography with noise-bias correction for optical coherence tomography of the retina
  
  Explore OSA | OSA Publishing Jan 13 2018 Ophthalmology
  
  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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  Mentions: Brett E. Bouma Massachusetts Institute of Technology Heidelberg Engineering
20. Diagnostic Capability of Peripapillary 3D Retinal Nerve Fiber Layer Volume for Glaucoma Using Optical Coherence Tomography Volume Scans
  
  Explore American Journal of Ophthalmology Aug 11 2017 Ophthalmology
  
  Purpose To determine the diagnostic capability of peripapillary 3-dimensional (3D) retinal nerve fiber layer (RNFL) volume measurements from spectral domain optical coherence tomography (OCT) volume scans for open angle glaucoma (OAG). Design Assessment of diagnostic accuracy. Methods Setting: Academic clinical setting. Study population : 180 patients (113 OAG and 67 normal subjects). Observation procedures : One eye per subject was included. Peripapillary 3D RNFL volumes were calculated for global, quadrant, and sector regions, using four different sized annuli. Peripapillary 2D RNFL thickness circle scans were also obtained. Main outcome measures : Area under the receiver operating characteristic curve (AUROC) values, sensitivity, specificity, positive ...
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  Mentions: Brett E. Bouma Johannes F. de Boer Massachusetts General Hospital
21. Simultaneous measurements of lymphatic vessel contraction, flow and valve dynamics in multiple lymphangions using optical coherence tomography
  
  Explore Wiley Online Library Jul 12 2017 Oncology
  
  Lymphatic dysfunction is involved in many diseases including lymphedema, hypertension, autoimmune responses, graft rejection, atherosclerosis, microbial infections, cancer and cancer metastasis. Expanding our knowledge of lymphatic system function can lead to a better understanding of these disease processes and improve treatment options. Here, optical coherence tomography (OCT) methods were used to reveal intraluminal valve dynamics in 3D, and measure lymph flow and vessel contraction simultaneously in three neighboring lymphangions of the afferent collecting lymphatic vessels to the popliteal lymph node in mice. Flow measurements were based on Doppler OCT techniques in combination with exogenous lymph labelling by Intralipid. Through these ...
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  Mentions: Massachusetts General Hospital Harvard University Benjamin J. Vakoc
22. Murine chronic lymph node window for longitudinal intravital lymph node imaging
  
  Explore Nature Publishing Group Jul 11 2017
  
  Chronic imaging windows in mice have been developed to allow intravital microscopy of many different organs and have proven to be of paramount importance in advancing our knowledge of normal and disease processes. A model system that allows long-term intravital imaging of lymph nodes would facilitate the study of cell behavior in lymph nodes during the generation of immune responses in a variety of disease settings and during the formation of metastatic lesions in cancer-bearing mice. We describe a chronic lymph node window (CLNW) surgical preparation that allows intravital imaging of the inguinal lymph node in mice. The CLNW is ...
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  Mentions: Massachusetts General Hospital Harvard University Sungkyunkwan University
23. 16 MHz wavelength-swept and wavelength-stepped laser architectures based on stretched-pulse active mode locking with a single continuously chirped fiber Bragg grating
  
  Explore OSA | OSA Publishing Jun 26 2017 Tunable Sources
  
  We demonstrate a novel high-speed and broadband laser architecture based on stretched pulse active mode locking that provides a wavelength-swept and wavelength-stepped output. The laser utilizes a single intracavity 8.3 meter chirped fiber Bragg grating to generate positive and negative dispersion, and can be operated with or without an intracavity fixed Fabry–Perot etalon to generate wavelength-swept and wavelength-stepped (frequency comb) outputs, respectively. Using a four-path delay line at the output, we achieved 16.3 MHz repetition rates and a 62 nm lasing bandwidth centered at 1550 nm. Single-sided double-pass coherence lengths of 1.25 mm for the wavelength-swept ...
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  Mentions: Massachusetts Institute of Technology Massachusetts General Hospital Harvard University
24. Laser thermal therapy monitoring using complex differential variance in optical coherence tomography
  
  Explore Wiley Online Library Sep 14 2016
  
  Conventional thermal therapy monitoring techniques based on temperature are often invasive, limited by point sampling, and are indirect measures of tissue injury, while techniques such as magnetic resonance and ultrasound thermometry are limited by their spatial resolution. The visualization of the thermal coagulation zone at high spatial resolution is particularly critical to the precise delivery of thermal energy to epithelial lesions. In this work, an integrated thulium laser thermal therapy monitoring system was developed based on complex differential variance (CDV), which enables the 2D visualization of the dynamics of the thermal coagulation process at high spatial and temporal resolution with ...
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  Mentions: Brett E. Bouma Massachusetts General Hospital Harvard University
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