1. Articles from Tristan T. Hormel

    1-9 of 9
    1. Automated segmentation of retinal fluid volumes from structural and angiographic optical coherence tomography using deep learning

      Automated segmentation of retinal fluid volumes from structural and angiographic optical coherence tomography using deep learning

      Purpose: We proposed a deep convolutional neural network (CNN), named Retinal Fluid Segmentation Network (ReF-Net) to segment volumetric retinal fluid on optical coherence tomography (OCT) volume. Methods: 3 × 3-mm OCT scans were acquired on one eye by a 70-kHz OCT commercial AngioVue system (RTVue-XR; Optovue, Inc.) from 51 participants in a clinical diabetic retinopathy (DR) study (45 with retinal edema and 6 healthy controls). A CNN with U-Net-like architecture was constructed to detect and segment the retinal fluid. Cross-sectional OCT and angiography (OCTA) scans were used for training and testing ReF-Net. The effect of including OCTA data for retinal fluid ...

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    2. Retinal capillary oximetry with visible light optical coherence tomography

      Retinal capillary oximetry with visible light optical coherence tomography

      Assessing oxygen saturation (sO 2 ) remains challenging but is nonetheless necessary for understanding retinal metabolism. We and others previously achieved oximetry on major retinal vessels and measured the total retinal oxygen metabolic rate in rats using visible-light optical coherence tomography. Here we extend oximetry measurements to capillaries and investigate all three retinal vascular plexuses by amplifying and extracting the spectroscopic signal from each capillary segment under the guidance of optical coherence tomography (OCT) angiography. Using this approach, we measured capillary sO 2 in the retinal circulation in rats, demonstrated reproducibility of the results, validated the measurements in superficial capillaries with ...

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    3. Imaging retinal structures at cellular-level resolution by visible-light optical coherence tomography

      Imaging retinal structures at cellular-level resolution by visible-light optical coherence tomography

      In vivo high-resolution images are the most direct way to understand retinal function and diseases. Here we report the use of visible-light optical coherence tomography with volumetric registration and averaging to achieve cellular-level retinal structural imaging in a rat eye, covering the entire depth of the retina. Vitreous fibers, nerve fiber bundles, and vasculature were clearly revealed, as well as at least three laminar sublayers in the inner plexiform layer. We also successfully visualized ganglion cell somas in the ganglion cell layer, cells in the inner nuclear layer, and photoreceptors in the outer nuclear layer and ellipsoid zone. This technique ...

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    4. 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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    5. Monitoring retinal responses to acute intraocular pressure elevation in rats with visible light optical coherence tomography

      Monitoring retinal responses to acute intraocular pressure elevation in rats with visible light optical coherence tomography

      Elevated intraocular pressure (IOP) is an important risk factor for glaucoma. However, the role of IOP in glaucoma progression, as well as retinal physiology in general, remains incompletely understood. We demonstrate the use of visible light optical coherence tomography to measure retinal responses to acute IOP elevation in Brown Norway rats. We monitored retinal responses in reflectivity, angiography, blood flow, oxygen saturation (sO2 ), and oxygen metabolism over a range of IOP from 10 to 100 mmHg. As IOP was elevated, nerve fiber layer reflectivity was found to decrease. Vascular perfusion in the three retinal capillary plexuses remained steady until IOP ...

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    6. High dynamic range optical coherence tomography angiography (HDR-OCTA)

      High dynamic range optical coherence tomography angiography (HDR-OCTA)

      The dynamic range of current optical coherence tomography (OCT) angiography (OCTA) images is limited by the fixed scanning intervals. High speed OCT devices introduce the possibility of extending the flow signal dynamic range. In this study, we created a novel scanning pattern for achieving high dynamic range (HDR)-OCTA with a superior scanning efficiency. We implemented a bidirectional, interleaved scanning pattern that is sensitive to different flow speeds by adjustable adjacent inter-scan time intervals. We found that an improved flow dynamic range can be achieved by generating 3 different B-scan time intervals using 3 repetitions.

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    7. Maximum value projection produces better en face OCT angiograms than mean value projection

      Maximum value projection produces better en face OCT angiograms than mean value projection

      Optical coherence tomography angiography (OCTA) images rely on en face data projections for both qualitative and quantitative interpretation. Both maximum value and mean value projections are commonly used, and many researchers consider them essentially interchangeable approaches. On the contrary, we find that maximum value projection achieves a consistently higher signal-to-noise ratio and higher image contrast across multiple vascular layers, in both healthy eyes and for each disease examined.

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    8. Real-time cross-sectional and en face OCT angiography guiding high-quality scan acquisition

      Real-time cross-sectional and en face OCT angiography guiding high-quality scan acquisition

      Defocusing, vignetting, and bulk motion degrade the image quality of optical coherence tomography angiography (OCTA) more significantly than structural OCT. The assessment of focus, alignment conditions, and stability of imaging subjects in commercially available OCTA systems are currently based on OCT signal quality alone, without knowledge of OCTA signal quality. This results in low yield rates for further quantification. In this Letter, we developed a novel OCTA platform based on a graphics processing unit (GPU) for a real-time, high refresh rate, B-san-by-B-scan split-spectrum amplitude-decorrelation angiography. The GPU provides a real-time display of both cross-sectional and en face images to assist ...

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    9. Automated phase unwrapping in Doppler optical coherence tomography

      Automated phase unwrapping in Doppler optical coherence tomography

      Phase wrapping is a crucial issue in Doppler optical coherence tomography (OCT) and restricts its automatic implementation for clinical applications that quantify total retinal blood flow. We propose an automated phase-unwrapping technique that takes advantage of the parabolic profile of blood flow velocity in vessels. Instead of inspecting the phase shift manually, the algorithm calculates the gradient magnitude of the phase shift on the cross-sectional image and automatically detects the presence of phase wrapping. The voxels affected by phase wrapping are corrected according to the determined flow direction adjacent to the vessel walls. We validated this technique in the rodent ...

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    1-9 of 9
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    Automated phase unwrapping in Doppler optical coherence tomography Real-time cross-sectional and en face OCT angiography guiding high-quality scan acquisition Maximum value projection produces better en face OCT angiograms than mean value projection High dynamic range optical coherence tomography angiography (HDR-OCTA) Monitoring retinal responses to acute intraocular pressure elevation in rats with visible light optical coherence tomography Automated segmentation of peripapillary retinal boundaries in OCT combining a convolutional neural network and a multi-weights graph search Imaging retinal structures at cellular-level resolution by visible-light optical coherence tomography Retinal capillary oximetry with visible light optical coherence tomography Automated segmentation of retinal fluid volumes from structural and angiographic optical coherence tomography using deep learning Systems and methods for reflectance-based projection-resolved optical coherence tomography angiography Health collaborations forged at CIIE begin to bear fruit Method for determining the topography of the cornea of an eye