1. Articles from Liang Liu

    1-21 of 21
    1. Sectorwise Visual Field Simulation Using Optical Coherence Tomographic Angiography Nerve Fiber Layer Plexus Measurements in Glaucoma

      Sectorwise Visual Field Simulation Using Optical Coherence Tomographic Angiography Nerve Fiber Layer Plexus Measurements in Glaucoma

      Purpose To simulate 24-2 visual field (VF) using optical coherence tomographic angiography (OCTA) for glaucoma evaluation. Design Cross-sectional study. Methods One eye each of 39 glaucoma and 31 age-matched normal participants was scanned using 4.5-mm OCTA scans centered on the disc. The peripapillary retinal nerve fiber layer plexus capillary density (NFLP_CD, %area) was measured. The NFLP_CD and 24-2 VF maps were divided into 8 corresponding sectors using an extension of Garway-Heath scheme. Results Sector NFLP_CD was transformed to a logarithmic dB scale and converted to sector simulated VF deviation maps. Comparing simulated and actual 24-2 VF maps, the worst ...

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    2. Measuring Glaucomatous Focal Perfusion Loss in the Peripapillary Retina using Optical Coherence Tomographic Angiography

      Measuring Glaucomatous Focal Perfusion Loss in the Peripapillary Retina using Optical Coherence Tomographic Angiography

      Purpose To measure low perfusion areas (LPA) and focal perfusion loss (FPL) in the peripapillary retina using optical coherence tomographic angiography (OCTA) in glaucoma. Design Prospective observation study. Participants Forty-seven primary open angle glaucoma (POAG) patients and 36 normal subjects were analyzed. Methods One eye of each subject was scanned using AngioVue 4.5-mm OCTA scan centered on the disc. En face nerve fiber layer plexus angiogram was generated. Using custom software, capillary density map was obtained by computing the fraction of area occupied by flow pixels within each superpixel containing 21×21-pixels. The low-perfusion map is defined by local ...

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    3. Automated segmentation of peripapillary retinal boundaries in OCT combining a convolutional neural network and a multi-weights graph search

      Automated segmentation of peripapillary retinal boundaries in OCT combining a convolutional neural network and a multi-weights graph search

      Quantitative analysis of the peripapillary retinal layers and capillary plexuses from optical coherence tomography (OCT) and OCT angiography images depend on two segmentation tasks – delineating the boundary of the optic disc and delineating the boundaries between retinal layers. Here, we present a method combining a neural network and graph search to perform these two tasks. A comparison of this novel method’s segmentation of the disc boundary showed good agreement with the ground truth, achieving an overall Dice similarity coefficient of 0.91 ± 0.04 in healthy and glaucomatous eyes. The absolute error of retinal layer boundaries segmentation in the ...

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    4. Signal strength reduction effects in optical coherence tomographic angiography

      Signal strength reduction effects in optical coherence tomographic angiography

      Objective To elucidate the relationship between vessel density (VD) measurements and signal strength in optical coherence tomography angiography (OCTA). Design Cross-sectional study. Subjects: Healthy volunteers. Methods OCTA images obtained from healthy volunteers were analyzed to demonstrate the relationship between signal strength index (SSI) and VD. Experiments were performed to determine the effects of signal strength reduction on VD measurements on the Optovue/AngioVue and Cirrus/AngioPlex OCTA systems. Signal strength reduction was generated by either neutral density filters (NDF) or defocus. Main Outcome Measures Regression analysis of signal strength effects on VD. Results VD decreased linearly with signal strength with ...

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    5. Automated detection of shadow artifacts in optical coherence tomography angiography

      Automated detection of shadow artifacts in optical coherence tomography angiography

      Frequently, when imaging retinal vasculature with optical coherence tomography angiography (OCTA) in diseased eyes, there are unavoidable obstacles to the propagation of light such as vitreous floaters or the pupil boundary. These obstacles can block the optical coherence tomography (OCT) beam and impede the visualization of the underlying retinal microcirculation. Detecting these shadow artifacts is especially important in the quantification of metrics that assess retinal disease progression because they might masquerade as regional perfusion loss. In this work, we present an algorithm to identify shadowed areas in OCTA of healthy subjects as well as patients with diabetic retinopathy, uveitis and ...

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    6. Nerve Fiber Flux Analysis Using Wide-Field Swept-Source Optical Coherence Tomography

      Nerve Fiber Flux Analysis Using Wide-Field Swept-Source Optical Coherence Tomography

      Purpose : To devise a method to quantify nerve fibers over their arcuate courses over an extended peripapillary area using optical coherence tomography (OCT). Methods : Participants were imaged with 8 × 8-mm volumetric OCT scans centered at the optic disc. A new quantity, nerve fiber flux (NFF), represents the cross-sectional area transected perpendicular to the nerve fibers. The peripapillary area was divided into 64 tracks with equal flux. An iterative algorithm traced the trajectory of the tracks assuming that the relative distribution of the NFF was conserved with compensation for fiber connections to ganglion cells on the macular side. Average trajectory was ...

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    7. OCT Angiography Changes in the 3 Parafoveal Retinal Plexuses in Response to Hyperoxia

      OCT Angiography Changes in the 3 Parafoveal Retinal Plexuses in Response to Hyperoxia

      Purpose Use projection-resolved OCT angiography to investigate the autoregulatory response in the 3 parafoveal retinal plexuses under hyperoxia. Design Prospective cohort study. Participants Nine eyes from 9 healthy participants. Methods One eye from each participant was scanned using a commercial spectral-domain OCT system. Two repeated macular scans (3 × 3 mm 2 ) were acquired at baseline and during oxygen breathing. The split-spectrum amplitude-decorrelation algorithm was used to detect blood flow. The projection-resolved algorithm was used to suppress projection artifacts and resolve blood flow in 3 distinct parafoveal plexuses. The Wilcoxon signed-rank test was used to compare baseline and hyperoxic parameters. The ...

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    8. Optical coherence tomography angiography enhances the detection of optic nerve damage in multiple sclerosis

      Optical coherence tomography angiography enhances the detection of optic nerve damage in multiple sclerosis

      Background Quantitative assessment of optic nerve damage is important in the evaluation of optic neuritis (ON) and multiple sclerosis (MS). Objective To detect optic nerve damage using optical coherence tomography (OCT) and OCT angiography in MS. Methods Peripapillary retinal nerve fibre layer (NFL) thickness, macular ganglion cell complex (GCC) thickness and Optic Nerve Head Flow Index (ONH-FI) were measured. The ONH-FI was defined as flow signal averaged over the optic disc. Diagnostic accuracy was evaluated by the area under the receiver-operating characteristics curve (AROC). Results Sixty-eight eyes of 45 MS participants and 55 eyes of 32 healthy controls (HCs) were ...

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    9. Optical Coherence Tomography Angiography of the Peripapillary Retina in Primary Angle-Closure Glaucoma

      Optical Coherence Tomography Angiography of the Peripapillary Retina in Primary Angle-Closure Glaucoma

      Purpose To measure the change of peripapillary retinal vessel density (VD) in eyes with a history of acute primary angle closure glaucoma (PACG). Design Case-control study. Methods Twenty-one consecutive Chinese patients with history of unilateral acute PACG were enrolled. Eyes with acute PACG constituted the case group, while the contralateral eyes without attack constituted the control. All patients underwent ophthalmic examinations including best-corrected visual acuity, intraocular pressure, and visual field (VF). Spectral-domain optical coherence tomography (SD-OCT) was used to obtain both structural OCT and OCT angiography (OCTA). Structural OCT scans provided thickness measurements of the peripapillary retinal nerve fiber layer ...

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    10. Projection-Resolved Optical Coherence Tomography Angiography of Macular Retinal Circulation in Glaucoma

      Projection-Resolved Optical Coherence Tomography Angiography of Macular Retinal Circulation in Glaucoma

      Purpose To detect macular perfusion defects in glaucoma using projection-resolved optical coherence tomography (OCT) angiography. Design Prospective observation study. Participants A total of 30 perimetric glaucoma and 30 age-matched normal participants were included. Methods One eye of each participant was imaged using 6 × 6–mm macular OCT angiography (OCTA) scan pattern by 70-kHz 840-nm spectral-domain OCT. Flow signal was calculated by the split-spectrum amplitude-decorrelation angiography algorithm. A projection-resolved OCTA (PR-OCTA) algorithm was used to remove flow projection artifacts. Four en face OCTA slabs were analyzed: the superficial vascular complex (SVC), intermediate capillary plexus (ICP), deep capillary plexus (DCP), and all-plexus ...

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    11. Handheld optical coherence tomography angiography

      Handheld optical coherence tomography angiography

      We developed a handheld optical coherence tomography angiography (OCTA) system using a 100-kHz swept-source laser. The handheld probe weighs 0.4 kg and measures 20.6 × 12.8 × 4.6 cm 3 . The system has dedicated features for handheld operation. The probe is equipped with a mini iris camera for easy alignment. Real-time display of the en face OCT and cross-sectional OCT images in the system allows accurately locating the imaging target. Fast automatic focusing was achieved by an electrically tunable lens controlled by a golden-section search algorithm. An extended axial imaging range of 6 mm allows easy alignment. A ...

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    12. Automated detection of dilated capillaries on optical coherence tomography angiography

      Automated detection of dilated capillaries on optical coherence tomography angiography

      Automated detection and grading of angiographic high-risk features in diabetic retinopathy can potentially enhance screening and clinical care. We have previously identified capillary dilation in angiograms of the deep plexus in optical coherence tomography angiography as a feature associated with severe diabetic retinopathy. In this study, we present an automated algorithm that uses hybrid contrast to distinguish angiograms with dilated capillaries from healthy controls and then applies saliency measurement to map the extent of the dilated capillary networks. The proposed algorithm agreed well with human grading.

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    13. Compensation for Reflectance Variation in Vessel Density Quantification by Optical Coherence Tomography Angiography

      Compensation for Reflectance Variation in Vessel Density Quantification by Optical Coherence Tomography Angiography

      Purpose : To compensate for reflectance variation when quantifying vessel density by optical coherence tomography angiography (OCTA). Methods : Healthy participants received 6×6-mm macular and 4.5×4.5-mm optic nerve head (ONH) angiography scans on a 70-kHz spectral-domain optical coherence tomography system. The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to compute the OCTA signal. Mean reflectance projection and maximum decorrelation projection were used to create en face OCT and OCTA images. Background OCTA noise in static tissue was evaluated in the foveal avascular zone (FAZ). Vessel density was calculated from en face retinal OCTA that was binarized according to ...

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    14. Retinal Blood Flow Response to Hyperoxia Measured With En Face Doppler Optical Coherence Tomography

      Retinal Blood Flow Response to Hyperoxia Measured With En Face Doppler Optical Coherence Tomography

      Purpose : To use multiplane en face Doppler optical coherence tomography (OCT) to measure the change in total retinal blood flow (TRBF) in response to hyperoxia. Methods : One eye of each healthy human participant ( n = 8) was scanned with a commercial high-speed (70-kHz) spectral OCT system. Three repeated scans were captured at baseline and after 10 minutes of oxygen (hyperoxia) by open nasal mask. The procedure was performed twice on day 1 and once more on day 2. Blood flow of each vein was estimated using Doppler OCT at an optimized en face plane. The TRBF was summed from all veins ...

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    15. Glaucoma Increases Retinal Surface Contour Variability as Measured by Optical Coherence Tomography

      Glaucoma Increases Retinal Surface Contour Variability as Measured by Optical Coherence Tomography

      Purpose : We investigated the feasibility of glaucoma detection by measuring retinal surface contour variability (RSCV) using optical coherence tomography (OCT). Methods : The peripapillary region in one eye of each participant was scanned over an 8 × 8 mm area with a swept source OCT prototype. The retinal surface contour was sampled at approximately 1.5- to 3.5-mm radius circles centered on the optic nerve head. The RSCV is defined as the average log value within a middle spatial frequency band of the Fourier transform to the elevation profile of the inner retinal surface. The spatial frequency band was optimized to ...

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    16. Automated volumetric segmentation of retinal fluid on optical coherence tomography

      Automated volumetric segmentation of retinal fluid on optical coherence tomography

      We propose a novel automated volumetric segmentation method to detect and quantify retinal fluid on optical coherence tomography (OCT). The fuzzy level set method was introduced for identifying the boundaries of fluid filled regions on B-scans (x and y-axes) and C-scans (z-axis). The boundaries identified from three types of scans were combined to generate a comprehensive volumetric segmentation of retinal fluid. Then, artefactual fluid regions were removed using morphological characteristics and by identifying vascular shadowing with OCT angiography obtained from the same scan. The accuracy of retinal fluid detection and quantification was evaluated on 10 eyes with diabetic macular edema ...

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    17. Automated Quantification of Capillary Nonperfusion Using Optical Coherence Tomography Angiography in Diabetic Retinopathy

      Automated Quantification of Capillary Nonperfusion Using Optical Coherence Tomography Angiography in Diabetic Retinopathy

      Importance Macular ischemia is a key feature of diabetic retinopathy (DR). Quantification of macular ischemia has potential as a biomarker for DR. Objective To assess the feasibility of automated quantification of capillary nonperfusion as a potential sign of macular ischemia using optical coherence tomography (OCT) angiography. Design, Setting, and Participants An observational study conducted in a tertiary, subspecialty, academic practice evaluated macular nonperfusion with 6 × 6-mm OCT angiography obtained with commercially available 70-kHz OCT and fluorescein angiography (FA). The study was conducted from January 22 to September 18, 2014. Data analysis was performed from October 1, 2014, to April 7 ...

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    18. Imaging the anterior eye with dynamic-focus swept-source optical coherence tomography.

      Imaging the anterior eye with dynamic-focus swept-source optical coherence tomography.

      A custom-built dynamic-focus swept-source optical coherence tomography (SS-OCT) system with a central wavelength of 1310 nm was used to image the anterior eye from the cornea to the lens. An electrically tunable lens was utilized to dynamically control the positions of focusing planes over the imaging range of 10 mm. The B-scan images were acquired consecutively at the same position but with different focus settings. The B-scan images were then registered and averaged after filtering the out-of-focus regions using a Gaussian window. By fusing images obtained at different depth focus locations, high-resolution and high signal-strength images were obtained over the ...

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    19. Advanced image processing for optical coherence tomographic angiography of macular diseases

      Advanced image processing for optical coherence tomographic angiography of macular diseases

      This article provides an overview of advanced image processing for three dimensional (3D) optical coherence tomographic (OCT) angiography of macular diseases, including age-related macular degeneration (AMD) and diabetic retinopathy (DR). A fast automated retinal layers segmentation algorithm using directional graph search was introduced to separates 3D flow data into different layers in the presence of pathologies. Intelligent manual correction methods are also systematically addressed which can be done rapidly on a single frame and then automatically propagated to full 3D volume with accuracy better than 1 pixel. Methods to visualize and analyze the abnormalities including retinal and choroidal neovascularization, retinal ...

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    20. Optical Coherence Tomography Angiography of Peripapillary Retinal Blood Flow Response to Hyperoxia

      Optical Coherence Tomography Angiography of Peripapillary Retinal Blood Flow Response to Hyperoxia

      Purpose. To measure the change in peripapillary retinal blood flow in response to hyperoxia by using optical coherence tomography (OCT) angiography. Methods. One eye of each healthy human participants (six) was scanned with a commercial high-speed (70 kHz) spectral OCT. Scans were captured twice after 10-minute exposures to normal breathing (baseline) and hyperoxia. Blood flow was detected by the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. Peripapillary retinal blood flow index and vessel density were calculated from en face maximum projections of the retinal layers. The experiment was performed on 2 separate days for each participant. Coefficient of variation (CV) was used ...

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    1-21 of 21
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    1. (21 articles) Oregon Health & Science University
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    3. (18 articles) Center for Ophthalmic Optics and Lasers
    4. (17 articles) Yali Jia
    5. (5 articles) Ou Tan
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    Optical Coherence Tomography Angiography of Peripapillary Retinal Blood Flow Response to Hyperoxia Advanced image processing for optical coherence tomographic angiography of macular diseases Imaging the anterior eye with dynamic-focus swept-source optical coherence tomography. Automated Quantification of Capillary Nonperfusion Using Optical Coherence Tomography Angiography in Diabetic Retinopathy Automated volumetric segmentation of retinal fluid on optical coherence tomography Retinal Blood Flow Response to Hyperoxia Measured With En Face Doppler Optical Coherence Tomography Compensation for Reflectance Variation in Vessel Density Quantification by Optical Coherence Tomography Angiography Automated detection of dilated capillaries on optical coherence tomography angiography Handheld optical coherence tomography angiography OCT Angiography Changes in the 3 Parafoveal Retinal Plexuses in Response to Hyperoxia Impact of cardiometabolic factors on retinal vasculature: A 3x3, 6x6 and 8x8-mm optical coherence tomography angiography study Quantitative research on the interaction between cerebral edema and peripheral cerebral blood perfusion using swept-source optical coherence tomography