1. Articles from Hao F. Zhang

    1-24 of 55 1 2 3 »
    1. Spectrally dependent roll-off in visible-light optical coherence tomography

      Spectrally dependent roll-off in visible-light optical coherence tomography

      Recent development of visible-light optical coherence tomography (vis-OCT) has introduced new applications for noninvasive spectroscopic imaging. However, the measured spectra may be altered by spectrally dependent roll-off (SDR). We formulated a mathematical model for SDR that accounted for nonuniform wavenumber spacing, optical aberrations, and misalignments in the spectrometer. We simulated SDR based on this model and found strong agreement with measurements from a vis-OCT system. We verified that SDR altered spectroscopic measurements of fully oxygenated blood. We corrected these alterations by normalizing each spectrally dependent A-line by the measured SDR of the spectrometer. Our investigations of SDR are critical for ...

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    2. In Vivo Imaging of Schlemm's Canal and Limbal Vascular Network in Mouse Using Visible-Light OCT

      In Vivo Imaging of Schlemm's Canal and Limbal Vascular Network in Mouse Using Visible-Light OCT

      Purpose : To validate the ability of visible-light optical coherence tomography (vis-OCT) in imaging the full Schlemm's canal (SC) and its surrounding limbal vascular network in mice in vivo through a compound circumlimbal scan. Methods : We developed an anterior segment vis-OCT system and a compound circumlimbal scanning method, which montages eight rotated raster scans. We calibrated the circumlimbal scan geometry using a three-dimensional printed phantom eyeball before imaging wild-type C57BL/6J mice. We measured SC size by segmenting SC cross sections from vis-OCT B-scan images and imaged the limbal microvascular network using vis-OCT angiography (vis-OCTA). To introduce changes in SC ...

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    3. VIS-OCT Opens Eyes to New Approaches

      VIS-OCT Opens Eyes to New Approaches

      First reported in 1991 by Huang and colleagues 1 , OCT has become an important imaging tool for ophthalmology following innovations over the past three decades. OCT noninvasively provides 3D in vivo optical biopsy with microscopic resolution in the eye at a depth range up to the choroid 2 . Besides 3D anatomical imaging, OCT can also provide functional information. The most notable functional extension is OCT angiography (OCTA), which can map the microvasculature in the eye without contrast agent and is being investigated in clinical ophthalmology.

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    4. Longitudinal deep-brain imaging in mouse using visible-light optical coherence tomography through chronic microprism cranial window

      Longitudinal deep-brain imaging in mouse using visible-light optical coherence tomography through chronic microprism cranial window

      We longitudinally imaged both the superficial and deep cortical microvascular networks in brains of healthy mice and in a mouse model of stroke in vivo using visible-light optical coherence tomography (vis-OCT). We surgically implanted a microprism in mouse brains sealed by a chronic cranial window. The microprism enabled vis-OCT to image the entire depth of the mouse cortex. Following microprism implantation, we imaged the mice for 28 days and found that that it took around 15 days for both the superficial and deep cortical microvessels to recover from the implantation surgery. After the brains recovered, we introduced ischemic strokes by ...

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    5. Speckle reduction in visible-light optical coherence tomography using scan modulation

      Speckle reduction in visible-light optical coherence tomography using scan modulation

      We present a technique to reduce speckle in visible-light optical coherence tomography (vis-OCT) that preserves fine structural details and is robust against sample motion. Specifically, we locally modulate B-scans orthogonally to their axis of acquisition. Such modulation enables acquisition of uncorrelated speckle patterns from similar anatomical locations, which can be averaged to reduce speckle. To verify the effectiveness of speckle reduction, we performed in-vivo retinal imaging using modulated raster and circular scans in both mice and humans. We compared speckle-reduced vis-OCT images with the images acquired with unmodulated B-scans from the same anatomical locations. We compared contrast-to-noise ratio (CNR) and ...

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    6. Designing visible-light optical coherence tomography towards clinics

      Designing visible-light optical coherence tomography towards clinics

      Background: The capabilities of visible-light optical coherence tomography (vis-OCT) in noninvasive anatomical and functional retinal imaging have been demonstrated by multiple groups in both rodents and healthy human subjects. Translating laboratory prototypes to an integrated clinical-environment-friendly system is required to explore the full potential of vis-OCT in disease management. Methods: We developed and optimized a portable vis-OCT system for human retinal imaging in clinical settings. We acquired raster- and circular-scan images from both healthy and diseased human eyes. Results: The new vis-OCT provided high-quality retinal images of both subjects without any known eye diseases and patients with various retinal diseases ...

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    7. Product Development Engineer Opening at Opticent Health

      Product Development Engineer Opening at Opticent Health

      Opticent, Inc. (Opticent Health – www.opticenthealth.com) , established in 2015, is a fast growing medical device start-up company commercializing visible-light optical coherence tomography (vis-OCT), a novel imaging modality for a variety of applications, including advanced ophthalmic diagnostics. First developed at Northwestern University, Opticent Health’s core technologies have been embraced by leading researchers in clinical and pre-clinical ophthalmic investigations, which has fueled rapid commercial development of vis-OCT products. Opticent Health is located in Evanston IL, part of the greater Chicago metropolitan area. The company’s management team, with guidance from its medical and technical advisory board, is expanding its engineering ...

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    8. Product Development Engineer Opening at Opticent Health

      Product Development Engineer Opening at Opticent Health

      Opticent, Inc. , established in 2015, is a fast growing medical device start-up company commercializing visible-light optical coherence tomography (vis-OCT), a novel imaging modality for a variety of applications, including advanced ophthalmic diagnostics. First developed at Northwestern University, Opticent Health’s core technologies have been embraced by leading researchers in clinical ophthalmic research which has fueled rapid commercial development of vis-OCT products. Opticent Health is located in Evanston IL, part of the greater Chicago metropolitan area. The company’s management team, with guidance from its medical and technical advisory board, is expanding its engineering staff for product development and seeks highly ...

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    9. Product Development Engineering Opening at Opticent Health.

      Product Development Engineering Opening at Opticent Health.

      Opticent, Inc. ( Opticent Health ) is a start-up company commercializing an in-house developed patent portfolio related to visible-light optical coherence tomography (OCT) targeting the ophthalmic market. Opticent Health’s core technologies were initially developed at Northwestern University. Since its founding, Opticent Health has experienced rapid market adoption of its OCT instruments and rapid commercial expansion. Opticent Health is located in Evanston IL, part of the greater Chicago metropolitan area. The company’s management team, with guidance from its prominent advisory board, is expanding its engineering staff and seeks highly qualified personnel for the following position: Product Development Engineer (software focus) Qualifications ...

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    10. Monitoring Acute Stroke in Mouse Model Using Laser Speckle Imaging-Guided Visible-Light Optical Coherence Tomography

      Monitoring Acute Stroke in Mouse Model Using Laser Speckle Imaging-Guided Visible-Light Optical Coherence Tomography

      Objective: Monitoring hemodynamic and vascular changes in the acute stages of mouse stroke models is invaluable in studying ischemic stroke pathophysiology. However, there lacks a tool to simultaneously and dynamically investigate these changes. Methods: We integrated laser speckle imaging (LSI) and visible-light optical coherence tomography (Vis-OCT) to reveal dynamic vascular responses in acute stages in the distal middle cerebral artery occlusion (dMCAO) model in rodents. LSI provides full-field, real-time imaging to guide Vis-OCT imaging and monitor the dynamic cerebral blood flow (CBF). Vis-OCT offers depth-resolved angiography and oxygen saturation (sO 2 ) measurements. Results: Our results showed detailed CBF and vasculature ...

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    11. Visible-light optical coherence tomography oximetry based on circumpapillary scan and graph-search segmentation

      Visible-light optical coherence tomography oximetry based on circumpapillary scan and graph-search segmentation

      Visible-light optical coherence tomography (vis-OCT) enables retinal oximetry by measuring the oxygen saturation of hemoglobin (sO 2 ) from within individual retinal blood vessels. The sO 2 calculation requires reliable estimation of the true spectrum of backscattered light from the posterior vessel wall. Unfortunately, subject motion and image noise make averaging from multiple A-lines at the same depth position challenging, and lead to inaccurate sO 2 estimation. In this study, we developed an algorithm to reliably extract the backscattered light’s spectrum. We used circumpapillary scanning to sample the vessels repeatedly at the same location. A combination of cross-correlation and graph-search ...

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    12. Visible-light optical coherence tomography: a review

      Visible-light optical coherence tomography: a review

      Visible-light optical coherence tomography (vis-OCT) is an emerging imaging modality, providing new capabilities in both anatomical and functional imaging of biological tissue. It relies on visible light illumination, whereas most commercial and investigational OCTs use near-infrared light. As a result, vis-OCT requires different considerations in engineering design and implementation but brings unique potential benefits to both fundamental research and clinical care of several diseases. Here, we intend to provide a summary of the development of vis-OCT and its demonstrated applications. We also provide perspectives on future technology improvement and applications.

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    13. Spectroscopic Doppler analysis for visible-light optical coherence tomography

      Spectroscopic Doppler analysis for visible-light optical coherence tomography

      Retinal oxygen metabolic rate can be effectively measured by visible-light optical coherence tomography (vis-OCT), which simultaneously quantifies oxygen saturation and blood flow rate in retinal vessels through spectroscopic analysis and Doppler measurement, respectively. Doppler OCT relates phase variation between sequential A-lines to the axial flow velocity of the scattering medium. The detectable phase shift is between − π −π and π π due to its periodicity, which limits the maximum measurable unambiguous velocity without phase unwrapping. Using shorter wavelengths, vis-OCT is more vulnerable to phase ambiguity since flow induced phase variation is linearly related to the center wavenumber of the probing light. We eliminated the ...

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    14. Two Engineering Openings at Startup Company Opticent Health

      Two Engineering Openings at Startup Company Opticent Health

      Opticent, Inc. (Opticent Health – www.opticenthealth.com) is a start-up company commercializing an in-house developed patent portfolio related to visible-light optical coherence tomography (OCT) targeting the ophthalmic market. Opticent Health’s core technologies were developed at Northwestern University. Since its founding, Opticent Health has experienced rapid market adoption of its OCT instruments and rapid commercial expansion. Opticent Health is located in Evanston IL, part of the greater Chicago metropolitan area. The company’s management team, with guidance from its prominent advisory board, is expanding its engineering staff and seeks highly qualified personnel for the following two positions: 1. Ph.D ...

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    15. Optical coherence tomography angiography of retinal vascular occlusions produced by imaging-guided laser photocoagulation

      Optical coherence tomography angiography of retinal vascular occlusions produced by imaging-guided laser photocoagulation

      Retinal vascular occlusive diseases represent a major form of vision loss worldwide. Rodent models of these diseases have traditionally relied upon a slit-lamp biomicroscope to help visualize the fundus and subsequently aid delivery of high-power laser shots to a target vessel. Here we describe a multimodal imaging system that can produce, image, and monitor retinal vascular occlusions in rodents. The system combines a spectral-domain optical coherence tomography system for cross-sectional structural imaging and three-dimensional angiography, and a fluorescence scanning laser ophthalmoscope for Rose Bengal monitoring and high-power laser delivery to a target vessel. This multimodal system facilitates the precise production ...

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    16. Colposcopic imaging using visible-light optical coherence tomography

      Colposcopic imaging using visible-light optical coherence tomography

      High-resolution colposcopic optical coherence tomography (OCT) provides key anatomical measures, such as thickness and minor traumatic injury of vaginal epithelium, of the female reproductive tract noninvasively. This information can be helpful in both fundamental investigations in animal models and disease screenings in humans. We present a fiber-based visible-light OCT and two probe designs for colposcopic application. One probe conducts circular scanning using a DC motor, and the other probe is capable of three-dimensional imaging over a 4.6 × 4.6 - mm 2 4.6×4.6-mm2 area using a pair of galvo scanners. Using this colposcopic vis-OCT with both probes ...

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    17. Devices, methods, and systems of functional optical coherence tomography

      Devices, methods, and systems of functional optical coherence tomography

      The present disclosure provides systems and methods for the determining a rate of change of one or more analyte concentrations in a target using non invasive non contact imaging techniques such as OCT. Generally, OCT data is acquired and optical information is extracted from OCT scans to quantitatively determine both a flow rate of fluid in the target and a concentration of one or more analytes. Both calculations can provide a means to determine a change in rate of an analyte over time. Example methods and systems of the disclosure may be used in assessing metabolism of a tissue, where ...

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    18. Retinal oximetry in humans using visible-light optical coherence tomography [Invited]

      Retinal oximetry in humans using visible-light optical coherence tomography [Invited]

      We measured hemoglobin oxygen saturation (sO 2 ) in the retinal circulation in healthy humans using visible-light optical coherence tomography (vis-OCT). The measurements showed clear oxygenation differences between central retinal arteries and veins close to the optic nerve head. Spatial variations at different vascular branching levels were also revealed. In addition, we presented theoretical and experimental results to establish that noises in OCT intensity followed Rice distribution. We used this knowledge to retrieve unbiased estimation of true OCT intensity to improve the accuracy of vis-OCT oximetry, which had inherently lower signal-to-nose ratio from human eyes due to safety and comfort limitations ...

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    19. Feature Of The Week 10/16/2016: Real-time Functional Analysis of Inertial Microfluidic Devices via Spectral Domain Optical Coherence Tomography

      Feature Of The Week 10/16/2016: Real-time Functional Analysis of Inertial Microfluidic Devices via Spectral Domain Optical Coherence Tomography

      Inertial microfluidic devices have recently attracted considerable interest due to their unique capability of high-throughput filtration, separation, and sorting of particles and live cells in a continuous flow manner. However, the underlying mechanism is not fully understood yet, which is due to limited options for real-time three-dimensional (3D) tracking and analysis of particles and live cells in microfluidic channels. Although micro-particle image velocimetry using optical confocal microscopy can be used to resolve the position of microparticles in 3D, it often requires exogenous labels to provide fluorescence contrast which is not always favorable for live cell analysis. To better understand the ...

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    20. Real-time Functional Analysis of Inertial Microfluidic Devices via Spectral Domain Optical Coherence Tomography

      Real-time Functional Analysis of Inertial Microfluidic Devices via Spectral Domain Optical Coherence Tomography

      We report the application of spectral-domain optical coherence tomography (SD-OCT) technology that enables real-time functional analysis of sorting microparticles and cells in an inertial microfluidic device. We demonstrated high-speed, high-resolution acquisition of cross-sectional images at a frame rate of 350 Hz, with a lateral resolution of 3 μm and an axial resolution of 1 μm within the microfluidic channel filled with water. We analyzed the temporal sequence of cross-sectional SD-OCT images to determine the position and diameter of microspheres in a spiral microfluidic channel under various flow rates. We used microspheres with known diameters to validate the sub-micrometer precision of ...

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    21. Imaging hemodynamic response after ischemic stroke in mouse cortex using visible-light optical coherence tomography

      Imaging hemodynamic response after ischemic stroke in mouse cortex using visible-light optical coherence tomography

      Visible-light optical coherence tomography (Vis-OCT) is an emerging technology that can image hemodynamic response in microvasculature. Vis-OCT can retrieve blood oxygen saturation (sO 2 ) mapping using intrinsic optical absorption contrast while providing high-resolution anatomical vascular structures at the same time. To improve the accuracy of Vis-OCT oximetry on vessels embedded in highly scattering medium, i.e., brain cortex, we developed and formulated a novel dual-depth sampling and normalization strategy that allowed us to minimize the detrimental effect of ubiquitous tissue scattering. We applied our newly developed approach to monitor the hemodynamic response in mouse cortex after focal photothrombosis. We observed ...

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    22. Postdoctoral Fellows Openings at Northwestern University

      Postdoctoral Fellows Openings at Northwestern University

      Functional Optical Imaging lab (FOIL) in the Department of Biomedical Engineering at Northwestern University develops optical imaging and sensing technologies for biomedical applications, including ophthalmology, vision science, neuroscience, HIV, and cancers. We are looking for two new postdoctoral fellows to join our extremely friendly, vibrant, productive, and collaborative group to develop novel optical microscopy technologies for ophthalmology and single-molecule imaging. We especially encourage applicants with extensive instrumentation and signal processing experiences in optical coherence tomography, ultra-fast optics, and super-resolution optical imaging. Experiences with small animal imaging, human retinal imaging, or cell culture and staining are also desired. The successful candidate ...

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    23. Visible-Light Optical Coherence Tomography Angiography for Monitoring Laser-Induced Choroidal Neovascularization in Mice

      Visible-Light Optical Coherence Tomography Angiography for Monitoring Laser-Induced Choroidal Neovascularization in Mice

      Purpose : This study sought to determine the earliest time-point at which evidence of choroidal neovascularization (CNV) could be detected with visible-light optical coherence tomography angiography (vis-OCTA) in a mouse model of laser-induced CNV. Methods : Visible light-OCTA was used to study laser-induced CNV at different time-points after laser injury to monitor CNV development and measure CNV lesion size. Measurements obtained from vis-OCTA angiograms were compared with histopathologic measurements from isolectin-stained choroidal flatmounts. Results : Choroidal neovascularization area measurements between the vis-OCTA system and isolectin-stained choroidal flatmounts were significantly different in area for days 2 to 4 postlaser injury, and were not significantly ...

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    24. Dual-band optical coherence tomography using a single supercontinuum laser source

      Dual-band optical coherence tomography using a single supercontinuum laser source

      We developed a simultaneous visible-light (Vis) and near-infrared (NIR) dual-band optical coherence tomography (OCT) system using a single supercontinuum laser source. The goal was to benchmark our newly developed Vis-OCT against the well-developed NIR-OCT. The Vis-OCT subsystem operated at 91 nm full-width-at-half-maximum (FWHM) bandwidth centered at 566 nm; the NIR-OCT subsystem operated at 93 nm FWHM bandwidth centered at 841 nm. The axial resolutions were 1.8 and 4.4    μ m 4.4  μm in air for the Vis- and NIR-OCT subsystems, respectively. We compared the respective performances, including anatomical imaging, angiography, absolute retinal blood flow measurements, and spectroscopic analysis ...

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    1-24 of 55 1 2 3 »
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    1. (53 articles) Hao F. Zhang
    2. (51 articles) Northwestern University
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    6. (9 articles) Opticent Health
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