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Ul Banna H, Mitchell B, Chen S, Palko J. Super-Resolution Ultrasound Localization Microscopy Using High-Frequency Ultrasound to Measure Ocular Perfusion Velocity in the Rat Eye. Bioengineering (Basel) 2023; 10:689. [PMID: 37370620 PMCID: PMC10295416 DOI: 10.3390/bioengineering10060689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Revised: 05/15/2023] [Accepted: 05/24/2023] [Indexed: 06/29/2023] Open
Abstract
Imaging of the ocular vasculature can provide new insights into the pathophysiology of ocular diseases. This study proposes a novel high-frequency super-resolution ultrasound localization microscopy (SRULM) technique and evaluates its ability to measure in vivo perfusion changes in the rat eye at elevated intraocular pressure (IOP). A 38.4 MHz center frequency linear array transducer on a VisualSonics Vevo F2 imaging platform was used to collect high frame rate (1 kHz) radiofrequency data of the posterior rat eye following systemic microbubble contrast injection. Following clutter and spatiotemporal non-local means filtering, individual microbubbles were localized and tracked. The microbubble tracks were accumulated over 10,000 frames to generate vascular images quantifying perfusion velocity and direction. Experiments were performed using physiologic relevant controlled flow states for algorithm validation and subsequently performed in vivo on the rat eye at 10 mm Hg IOP increments from 10 to 60 mm Hg. The posterior vasculature of the rat eye, including the ophthalmic artery, long posterior ciliary arteries and their branches, central retinal artery and retinal arterioles and venules were successfully visualized, and velocities quantified at each IOP level. Significant reductions in arterial flow were measured as IOP was elevated. High-frequency SRULM can be used to visualize and quantify the perfusion velocity of the rat eye in both the retrobulbar and intraocular vasculature simultaneously. The ability to detect ocular perfusion changes throughout the depth of the eye may help elucidate the role ischemia has in the pathophysiology of ocular diseases such as glaucoma.
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Affiliation(s)
- Hasan Ul Banna
- Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV 26505, USA
| | - Benjamin Mitchell
- Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV 26505, USA
| | - Stephen Chen
- School of Medicine, West Virginia University, Morgantown, WV 26505, USA
| | - Joel Palko
- Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV 26505, USA
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Girkin CA, Garner MA, Fazio MA, Clark ME, Karuppanan U, Hubbard MG, Bianco G, Hubbard ST, Fortune B, Gross AK. Retinal electrophysiologic response to IOP elevation in living human eyes. Exp Eye Res 2023; 229:109420. [PMID: 36806673 PMCID: PMC11048619 DOI: 10.1016/j.exer.2023.109420] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Revised: 01/26/2023] [Accepted: 02/15/2023] [Indexed: 02/18/2023]
Abstract
PURPOSE The relationships between intraocular pressure (IOP), ocular perfusion pressure (OPP), retinal perfusion, and retinal electrophysiologic responses have been explored experimentally across several animal models. These studies have demonstrated that elevated IOP reduces OPP, and when this reduction in OPP exceeds the autoregulatory capacity of the retina vasculature, retinal perfusion and electrophysiologic responses are reduced. This study aimed to evaluate these interactions for the first time in the living human eye. METHODS Five eyes from three research-consented brain-dead organ donors underwent optical coherence tomography with angiographic (OCT/A; Spectralis, Heidelberg Engineering) and electroretinographic (ERG, Diagnosys LLC) measurements while IOP was manometrically-elevated stepwise to pressures of 10, 30 and 50 mmHg. Systemic blood pressure (BP) was monitored continuously during testing. Correlation analysis was applied to assess association between ERG and OPP changes. In a single eye, prolonged IOP elevation was induced with viscoelastic injection and serial ERG measurements were obtained. RESULTS Reductions in inner retinal function defined by photopic ERG were observed with elevation in IOP and concomitant reduction in OPP. Reductions, especially in b-wave, and photopic negative response (PhNR) amplitudes and implicit times were significantly correlated with elevation in IOP and reduction in OPP. There were more appreciable changes in perfusion and functional responses in eyes tested while systemic blood pressure was lower. With prolonged IOP elevation, selective loss of the PhNR response was observed. CONCLUSIONS In the living human eye, retinal perfusion and inner retinal function are acutely impacted by elevation of IOP, and this impact is related to systemic BP and OPP. This novel approach provides a viable model to study the autoregulatory responses to IOP elevation in the living human eye.
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Affiliation(s)
- Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States.
| | - Mary Anne Garner
- Department of Neurobiology, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States
| | - Massimo A Fazio
- Department of Ophthalmology and Visual Sciences, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States; Hamilton Glaucoma Center, Shiley Eye Institute, The Viterbi Family Department of Ophthalmology, University of California San Diego, La Jolla, CA, United States
| | - Mark E Clark
- Department of Ophthalmology and Visual Sciences, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States
| | - Udayakumar Karuppanan
- Department of Ophthalmology and Visual Sciences, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States
| | - Meredith G Hubbard
- Department of Ophthalmology and Visual Sciences, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States; Department of Neurobiology, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States
| | - Gianfranco Bianco
- Department of Ophthalmology and Visual Sciences, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States
| | - Seth T Hubbard
- Department of Neurobiology, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States; Science and Technology Honors Program, The University of Alabama at Birmingham, Birmingham, AL, United States
| | - Brad Fortune
- Devers Eye Institute, Legacy Health, Portland, OR, United States
| | - Alecia K Gross
- Department of Neurobiology, The University of Alabama at Birmingham School of Medicine, Birmingham, AL, United States
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Rahimi M, Leahy S, Matei N, Burford J, Blair NP, Shahidi M. Impairments of retinal hemodynamics and oxygen metrics in ocular hypertension-induced ischemia-reperfusion. Exp Eye Res 2022; 225:109278. [PMID: 36252653 PMCID: PMC10985794 DOI: 10.1016/j.exer.2022.109278] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Revised: 08/23/2022] [Accepted: 10/10/2022] [Indexed: 12/29/2022]
Abstract
Ischemia-reperfusion (I/R) is an established model for retinal neurodegeneration. However, there is limited knowledge of retinal physiological metrics and their relationships to retinal function and morphology in the I/R model. The purpose of the study was to test the hypotheses that retinal hemodynamic and oxygen metrics are impaired and associated with visual dysfunction, retinal thinning, and retinal ganglion cell (RGC) loss due to I/R injury. Intraocular pressure (IOP) was increased in one eye of 10 rats for 90 min followed by reperfusion. Fellow eyes served as controls. After one week of reperfusion, multimodal imaging was performed to quantify total retinal blood flow (TRBF) and retinal vascular oxygen contents. Retinal oxygen delivery (DO2) and metabolism (MO2) were calculated. Pattern-evoked electroretinography (PERG) and optical coherence tomography were performed to measure RGC function and retinal thicknesses, respectively. RGCs were counted from retina whole mounts. After one week of reperfusion, TRBF was lower in study eyes than in control eyes (p < 0.0003). Similarly, DO2 and MO2 were reduced in study eyes compared to control eyes (p < 0.003). PERG amplitude, TRT, IRT, ORT, and RGCs were also lower in study eyes (p ≤ 0.01). DO2 and MO2 were correlated with PERG amplitude, TRT, IRT, and ORT (r ≥ 0.6, p ≤ 0.005). The findings improve knowledge of physiological metrics affected by I/R injury and have the potential for identifying biomarkers of injury and outcomes for evaluating experimental treatments.
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Affiliation(s)
- Mansour Rahimi
- USC Roski Eye Institute, Department of Ophthalmology, Keck School of Medicine of University of Southern California, Los Angeles, CA, 90033, USA
| | - Sophie Leahy
- USC Roski Eye Institute, Department of Ophthalmology, Keck School of Medicine of University of Southern California, Los Angeles, CA, 90033, USA
| | - Nathanael Matei
- USC Roski Eye Institute, Department of Ophthalmology, Keck School of Medicine of University of Southern California, Los Angeles, CA, 90033, USA
| | - James Burford
- USC Roski Eye Institute, Department of Ophthalmology, Keck School of Medicine of University of Southern California, Los Angeles, CA, 90033, USA
| | - Norman P Blair
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, USA
| | - Mahnaz Shahidi
- USC Roski Eye Institute, Department of Ophthalmology, Keck School of Medicine of University of Southern California, Los Angeles, CA, 90033, USA.
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Retinal blood flow reversal quantitatively monitored in out-of-plane vessels with laser Doppler holography. Sci Rep 2021; 11:17828. [PMID: 34497299 PMCID: PMC8426375 DOI: 10.1038/s41598-021-96877-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Accepted: 08/05/2021] [Indexed: 12/29/2022] Open
Abstract
Laser Doppler holography is a planar blood flow imaging technique recently introduced in ophthalmology to image human retinal and choroidal blood flow non-invasively. Here we present a digital method based on the Doppler spectrum asymmetry that reveals the local direction of blood flow with respect to the optical axis in out-of-plane vessels. This directional information is overlaid on standard grayscale blood flow images to depict flow moving towards the camera in red and flow moving away from the camera in blue, as in ultrasound color Doppler imaging. We show that thanks to the strong contribution of backscattering to the Doppler spectrum in out-of-plane vessels, the local axial direction of blood flow can be revealed with a high temporal resolution, which enables us to evidence pathological blood flow reversals. We also demonstrate the use of optical Doppler spectrograms to quantitatively monitor retinal blood flow reversals.
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Silverman RH, Urs R, Tezel G, Yang X, Nelson I, Ketterling JA. Retrobulbar blood flow in rat eyes during acute elevation of intraocular pressure. Exp Eye Res 2021; 207:108606. [PMID: 33930396 DOI: 10.1016/j.exer.2021.108606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 04/12/2021] [Accepted: 04/22/2021] [Indexed: 10/21/2022]
Abstract
Most studies of the effect of acute elevation of intraocular pressure (IOP) on ocular blood-flow have utilized optical coherence tomography (OCT) to characterize retinal and choroidal flow and vascular density. This study investigates the effect of acute IOP elevation on blood flow velocity in the retrobulbar arteries and veins supplying and draining the eye, which, unlike the retinal and choroidal vasculature, are not directly compressed as IOP is increased. By cannulation of the anterior chamber of 20 Sprague-Dawley rats, we increased IOP in 10 mmHg steps from 10 to 60 mmHg and returned to 10 mmHg. After 1 min at each IOP (and 3 min after return to 10 mmHg), we acquired 18 MHz plane-wave ultrasound data at 3000 compound images/sec for 1.5 s. We produced color-flow Doppler images by digital signal processing of the ultrasound data, identified retrobulbar arteries and veins, generated spectrograms depicting flow velocity over the cardiac cycle and characterized changes of vascular density and perfusion in the orbit overall. Systolic, diastolic and mean velocities and resistive and pulsatile indices were determined from arterial spectrograms at each IOP level. Baseline mean arterial and mean venous velocities averaged 30.9 ± 10.8 and 8.5 ± 3.3 mm/s, respectively. Arterial velocity progressively decreased and resistance indices increased at and above an IOP of 30 mmHg. Mean arterial velocity at 60 mmHg dropped by 55% with respect to baseline, while venous velocity decreased by 20%. Arterial and venous velocities and resistance returned to near baseline after IOP was restored to 10 mmHg. Both vascular density and orbital perfusion decreased with IOP, but while perfusion returned to near normal when IOP returned to 10 mmHg, density remained reduced. Our findings are consistent with OCT-based studies showing reduced perfusion of the retina at levels comparable to retrobulbar arterial flow velocity change with increased IOP. The lesser effect on venous flow is possibly attributable to partial collapse of the venous lumen as volumetric venous outflow decreased at high IOP. The continued reduction in orbital vascular density 3 min after restoration of IOP to 10 mmHg might be attributable to persisting narrowing of capillaries, but this needs to be verified in future studies.
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Affiliation(s)
- Ronald H Silverman
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, NY, USA.
| | - Raksha Urs
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, NY, USA
| | - Gulgun Tezel
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, NY, USA
| | - Xiangjun Yang
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, NY, USA
| | - Inez Nelson
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, NY, USA
| | - Jeffrey A Ketterling
- F.L. Lizzi Center for Biomedical Engineering, Riverside Research, New York, NY, USA
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Courtie E, Veenith T, Logan A, Denniston AK, Blanch RJ. Retinal blood flow in critical illness and systemic disease: a review. Ann Intensive Care 2020; 10:152. [PMID: 33184724 PMCID: PMC7661622 DOI: 10.1186/s13613-020-00768-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 10/23/2020] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Assessment and maintenance of end-organ perfusion are key to resuscitation in critical illness, although there are limited direct methods or proxy measures to assess cerebral perfusion. Novel non-invasive methods of monitoring microcirculation in critically ill patients offer the potential for real-time updates to improve patient outcomes. MAIN BODY Parallel mechanisms autoregulate retinal and cerebral microcirculation to maintain blood flow to meet metabolic demands across a range of perfusion pressures. Cerebral blood flow (CBF) is reduced and autoregulation impaired in sepsis, but current methods to image CBF do not reproducibly assess the microcirculation. Peripheral microcirculatory blood flow may be imaged in sublingual and conjunctival mucosa and is impaired in sepsis. Retinal microcirculation can be directly imaged by optical coherence tomography angiography (OCTA) during perfusion-deficit states such as sepsis, and other systemic haemodynamic disturbances such as acute coronary syndrome, and systemic inflammatory conditions such as inflammatory bowel disease. CONCLUSION Monitoring microcirculatory flow offers the potential to enhance monitoring in the care of critically ill patients, and imaging retinal blood flow during critical illness offers a potential biomarker for cerebral microcirculatory perfusion.
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Affiliation(s)
- E Courtie
- Neuroscience and Ophthalmology, Institute of Inflammation and Ageing, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
- Ophthalmology Department, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK
- NIHR Surgical Reconstruction and Microbiology Research Centre, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK
| | - T Veenith
- Critical Care Unit, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK
- Birmingham Acute Care Research Group, Institute of Inflammation and Ageing, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - A Logan
- Axolotl Consulting Ltd, Droitwich, WR9 0JS, Worcestershire, UK
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7HL, UK
| | - A K Denniston
- Neuroscience and Ophthalmology, Institute of Inflammation and Ageing, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
- Ophthalmology Department, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK
- NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
- Centre for Rare Diseases, Institute of Translational Medicine, Birmingham Health Partners, Birmingham, UK
| | - R J Blanch
- Neuroscience and Ophthalmology, Institute of Inflammation and Ageing, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
- Ophthalmology Department, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK.
- NIHR Surgical Reconstruction and Microbiology Research Centre, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK.
- Academic Department of Military Surgery and Trauma, Royal Centre for Defence Medicine, Birmingham, UK.
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7
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Miller DA, Grannonico M, Liu M, Kuranov RV, Netland PA, Liu X, Zhang HF. Visible-Light Optical Coherence Tomography Fibergraphy for Quantitative Imaging of Retinal Ganglion Cell Axon Bundles. Transl Vis Sci Technol 2020; 9:11. [PMID: 33110707 PMCID: PMC7552935 DOI: 10.1167/tvst.9.11.11] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Accepted: 09/18/2020] [Indexed: 01/15/2023] Open
Abstract
Purpose To develop a practical technique for visualizing and quantifying retinal ganglion cell (RGC) axon bundles in vivo. Methods We applied visible-light optical coherence tomography (vis-OCT) to image the RGC axon bundles, referred to as vis-OCT fibergraphy, of healthy wild-type C57BL/6 mice. After vis-OCT imaging, retinas were flat-mounted, immunostained with anti-beta-III tubulin (Tuj1) antibody for RGC axons, and imaged with confocal microscopy. We quantitatively compared the RGC axon bundle networks imaged by in vivo vis-OCT and ex vivo confocal microscopy using semi-log Sholl analysis. Results Side-by-side comparison of ex vivo confocal microscopy and in vivo vis-OCT confirmed that vis-OCT fibergraphy captures true RGC axon bundle networks. The semi-log Sholl regression coefficients extracted from vis-OCT fibergrams (3.7 ± 0.8 mm–1) and confocal microscopy (3.6 ± 0.3 mm–1) images also showed good agreement with each other (n = 6). Conclusions We demonstrated the feasibility of using vis-OCT fibergraphy to visualize RGC axon bundles. Further applying Sholl analysis has the potential to identify biomarkers for non-invasively assessing RGC health. Translational Relevance Our novel technique for visualizing and quantifying RGC axon bundles in vivo provides a potential measurement tool for diagnosing and tracking the progression of optic neuropathies.
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Affiliation(s)
- David A Miller
- Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA
| | - Marta Grannonico
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Mingna Liu
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Roman V Kuranov
- Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA.,Opticent Health, Evanston, IL, USA
| | - Peter A Netland
- Department of Ophthalmology, University of Virginia, Charlottesville, VA, USA
| | - Xiaorong Liu
- Department of Biology, University of Virginia, Charlottesville, VA, USA.,Department of Psychology, University of Virginia, Charlottesville, VA, USA
| | - Hao F Zhang
- Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA.,Department of Ophthalmology, Northwestern University, Evanston, IL, USA
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Song W, Shao W, Yi W, Liu R, Desai M, Ness S, Yi J. Visible light optical coherence tomography angiography (vis-OCTA) facilitates local microvascular oximetry in the human retina. BIOMEDICAL OPTICS EXPRESS 2020; 11:4037-4051. [PMID: 33014584 PMCID: PMC7510897 DOI: 10.1364/boe.395843] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 06/18/2020] [Accepted: 06/22/2020] [Indexed: 05/06/2023]
Abstract
We report herein the first visible light optical coherence tomography angiography (vis-OCTA) for human retinal imaging. Compared to the existing vis-OCT systems, we devised a spectrometer with a narrower bandwidth to increase the spectral power density for OCTA imaging, while retaining the major spectral contrast in the blood. We achieved a 100 kHz A-line rate, the fastest acquisition speed reported so far for human retinal vis-OCT. We rigorously optimized the imaging protocol such that a single acquisition took < 6 seconds with a field of view (FOV) of 3×7.8 mm2. The angiography enables accurate localization of microvasculature down to the capillary level and thus enables oximetry at vessels < 100 µm in diameter. We demonstrated microvascular hemoglobin oxygen saturation (sO2) at the feeding and draining vessels at the perifoveal region. The longitudinal repeatability was assessed by < 5% coefficient of variation (CV). The unique capabilities of our vis-OCTA system may allow studies on the role of microvascular oxygen in various retinal pathologies.
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Affiliation(s)
- Weiye Song
- Department of Medicine, Boston University School of Medicine, Boston Medical Center, Boston 02118, USA
| | - Wenjun Shao
- Department of Medicine, Boston University School of Medicine, Boston Medical Center, Boston 02118, USA
| | - Wei Yi
- Department of Medicine, Boston University School of Medicine, Boston Medical Center, Boston 02118, USA
| | - Rongrong Liu
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA
| | - Manishi Desai
- Department of Ophthalmology, Boston University School of Medicine, Boston Medical Center, Boston 02118, USA
| | - Steven Ness
- Department of Ophthalmology, Boston University School of Medicine, Boston Medical Center, Boston 02118, USA
| | - Ji Yi
- Department of Medicine, Boston University School of Medicine, Boston Medical Center, Boston 02118, USA
- Department of Biomedical Engineering, Boston University, Boston 02118, USA
- Department of Electronic and Computer Engineering, Boston University, Boston 02118, USA
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9
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Retinal capillary oximetry with visible light optical coherence tomography. Proc Natl Acad Sci U S A 2020; 117:11658-11666. [PMID: 32398376 DOI: 10.1073/pnas.1918546117] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Assessing oxygen saturation (sO2) 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 sO2 in the retinal circulation in rats, demonstrated reproducibility of the results, validated the measurements in superficial capillaries with known perfusion pathways, and determined sO2 responses to hypoxia and hyperoxia in the different retinal capillary beds. OCT capillary oximetry has the potential to provide new insights into the retinal circulation in the normal eye as well as in retinal vascular diseases.
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Pi S, Hormel TT, Wei X, Cepurna W, Morrison JC, Jia Y. Imaging retinal structures at cellular-level resolution by visible-light optical coherence tomography. OPTICS LETTERS 2020; 45:2107-2110. [PMID: 32236080 PMCID: PMC8575555 DOI: 10.1364/ol.386454] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 03/05/2020] [Indexed: 05/10/2023]
Abstract
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 provides, to the best of our knowledge, a new means to visualize the retina in vivo at a cellular resolution and may enable detection or discovery of cellular neuronal biomarkers to help better diagnose ocular disease.
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Affiliation(s)
- Shaohua Pi
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
| | - Tristan T. Hormel
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
| | - Xiang Wei
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
| | - William Cepurna
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
| | - John C. Morrison
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
| | - Yali Jia
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
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12
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Liu R, Cheng S, Tian L, Yi J. Deep spectral learning for label-free optical imaging oximetry with uncertainty quantification. LIGHT, SCIENCE & APPLICATIONS 2019; 8:102. [PMID: 31754429 PMCID: PMC6864044 DOI: 10.1038/s41377-019-0216-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Revised: 10/17/2019] [Accepted: 11/01/2019] [Indexed: 05/06/2023]
Abstract
Measurement of blood oxygen saturation (sO2) by optical imaging oximetry provides invaluable insight into local tissue functions and metabolism. Despite different embodiments and modalities, all label-free optical-imaging oximetry techniques utilize the same principle of sO2-dependent spectral contrast from haemoglobin. Traditional approaches for quantifying sO2 often rely on analytical models that are fitted by the spectral measurements. These approaches in practice suffer from uncertainties due to biological variability, tissue geometry, light scattering, systemic spectral bias, and variations in the experimental conditions. Here, we propose a new data-driven approach, termed deep spectral learning (DSL), to achieve oximetry that is highly robust to experimental variations and, more importantly, able to provide uncertainty quantification for each sO2 prediction. To demonstrate the robustness and generalizability of DSL, we analyse data from two visible light optical coherence tomography (vis-OCT) setups across two separate in vivo experiments on rat retinas. Predictions made by DSL are highly adaptive to experimental variabilities as well as the depth-dependent backscattering spectra. Two neural-network-based models are tested and compared with the traditional least-squares fitting (LSF) method. The DSL-predicted sO2 shows significantly lower mean-square errors than those of the LSF. For the first time, we have demonstrated en face maps of retinal oximetry along with a pixel-wise confidence assessment. Our DSL overcomes several limitations of traditional approaches and provides a more flexible, robust, and reliable deep learning approach for in vivo non-invasive label-free optical oximetry.
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Affiliation(s)
- Rongrong Liu
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208 USA
| | - Shiyi Cheng
- Department of Electrical and Computer Engineering, Boston University, Boston, MA 02215 USA
| | - Lei Tian
- Department of Electrical and Computer Engineering, Boston University, Boston, MA 02215 USA
| | - Ji Yi
- Department of Electrical and Computer Engineering, Boston University, Boston, MA 02215 USA
- Department of Biomedical Engineering, Boston University, Boston, MA 02215 USA
- Department of Medicine, Boston University School of Medicine, Boston Medical Center, Boston, MA 02118 USA
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