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Jo HC, Jeong H, Lee J, Na KS, Kim DY. Quantification of Blood Flow Velocity in the Human Conjunctival Microvessels Using Deep Learning-Based Stabilization Algorithm. SENSORS 2021; 21:s21093224. [PMID: 34066590 PMCID: PMC8124391 DOI: 10.3390/s21093224] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 04/30/2021] [Accepted: 05/01/2021] [Indexed: 11/27/2022]
Abstract
The quantification of blood flow velocity in the human conjunctiva is clinically essential for assessing microvascular hemodynamics. Since the conjunctival microvessel is imaged in several seconds, eye motion during image acquisition causes motion artifacts limiting the accuracy of image segmentation performance and measurement of the blood flow velocity. In this paper, we introduce a novel customized optical imaging system for human conjunctiva with deep learning-based segmentation and motion correction. The image segmentation process is performed by the Attention-UNet structure to achieve high-performance segmentation results in conjunctiva images with motion blur. Motion correction processes with two steps—registration and template matching—are used to correct for large displacements and fine movements. The image displacement values decrease to 4–7 μm during registration (first step) and less than 1 μm during template matching (second step). With the corrected images, the blood flow velocity is calculated for selected vessels considering temporal signal variances and vessel lengths. These methods for resolving motion artifacts contribute insights into studies quantifying the hemodynamics of the conjunctiva, as well as other tissues.
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Affiliation(s)
- Hang-Chan Jo
- Department of Electrical and Computer Engineering, Inha University, Incheon 22212, Korea; (H.-C.J.); (H.J.); (J.L.)
- Center for Sensor Systems, Inha University, Incheon 22212, Korea
| | - Hyeonwoo Jeong
- Department of Electrical and Computer Engineering, Inha University, Incheon 22212, Korea; (H.-C.J.); (H.J.); (J.L.)
| | - Junhyuk Lee
- Department of Electrical and Computer Engineering, Inha University, Incheon 22212, Korea; (H.-C.J.); (H.J.); (J.L.)
| | - Kyung-Sun Na
- Department of Ophthalmology & Visual Science, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul 07345, Korea
- Correspondence: (K.-S.N.); (D.-Y.K.); Tel.: +82-02-3779-1520 (K.-S.N.); +82-32-860-7394 (D.-Y.K.)
| | - Dae-Yu Kim
- Department of Electrical and Computer Engineering, Inha University, Incheon 22212, Korea; (H.-C.J.); (H.J.); (J.L.)
- Center for Sensor Systems, Inha University, Incheon 22212, Korea
- Inha Research Institute for Aerospace Medicine, Inha University, Incheon 22212, Korea
- Correspondence: (K.-S.N.); (D.-Y.K.); Tel.: +82-02-3779-1520 (K.-S.N.); +82-32-860-7394 (D.-Y.K.)
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Quantification of ocular surface microcirculation by computer assisted video microscopy and diffuse reflectance spectroscopy. Exp Eye Res 2020; 201:108312. [PMID: 33157128 PMCID: PMC7581323 DOI: 10.1016/j.exer.2020.108312] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 10/13/2020] [Accepted: 10/15/2020] [Indexed: 11/22/2022]
Abstract
In piglets we tested the applicability of digital video microscopy and diffuse reflectance spectroscopy for non-invasive assessments of limbal and bulbar conjunctival microcirculation. A priori we postulated that the metabolic rate is higher in limbal as compared to bulbar conjunctiva, and that this difference is reflected in microvascular structure or function between the two locations. Two study sites, Oslo University Hospital (OUH), Norway and Cleveland Clinic (CC), USA, used the same video microscopy and spectroscopy techniques to record limbal and bulbar microcirculation in sleeping piglets. Recordings were analyzed with custom-made software to quantify functional capillary density, capillary flow velocity and microvascular oxygen saturation in measuring volumes of approximately 0.1 mm3. The functional capillary density was higher in limbus than in bulbar conjunctiva at both study sites (OUH: 18.1 ± 2.9 versus 12.2 ± 2.9 crossings per mm line, p < 0.01; CC: 11.3 ± 3.0 versus 7.1 ± 2.8 crossings per mm line, p < 0.01). Median categorial capillary blood flow velocity was higher in bulbar as compared with limbal recordings (CC: 3 (1-3) versus 1 (0-3), p < 0.01). Conjunctival microvascular oxygen saturation was 88 ± 5.9% in OUH versus 94 ± 7.5% in CC piglets. Non-invasive digital video microscopy and diffuse reflectance spectroscopy can be used to obtain data from conjunctival microcirculation in piglets. Limbal conjunctival microcirculation has a larger capacity for oxygen delivery as compared with bulbar conjunctiva.
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Simkiene J, Pranskuniene Z, Vitkauskiene A, Pilvinis V, Boerma EC, Pranskunas A. Ocular microvascular changes in patients with sepsis: a prospective observational study. Ann Intensive Care 2020; 10:38. [PMID: 32266602 PMCID: PMC7138894 DOI: 10.1186/s13613-020-00655-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 03/24/2020] [Indexed: 12/11/2022] Open
Abstract
Background The aim of the study was to detect differences in the conjunctival microcirculation between septic patients and healthy subjects and to evaluate the course of conjunctival and retinal microvasculature in survivors and non-survivors over a 24-h period of time. Methods This single-center prospective observational study was performed in mixed ICU in a tertiary teaching hospital. We included patients with sepsis or septic shock within the first 24 h after ICU admission. Conjunctival imaging, using an IDF video microscope, and retinal imaging, using portable digital fundus camera, as well as systemic hemodynamic measurements, were performed at three time points: at baseline, 6 h and 24 h. Baseline conjunctival microcirculatory parameters were compared with healthy controls. Results A total of 48 patients were included in the final assessment and analysis. Median APACHE II and SOFA scores were 16[12–21] and 10[7–12], respectively. Forty-four (92%) patients were in septic shock, 48 (100%) required mechanical ventilation. 19 (40%) patients were discharged alive from the intensive care unit. We found significant reductions in all microcirculatory parameters in the conjunctiva when comparing septic and healthy subjects. In addition, we observed a significant lower microvascular flow index (MFI) of small conjunctival vessels during all three time points in non-survivors compared with survivors. However, retinal arteriolar vessels were not different between survivors and non-survivors. Conclusions Conjunctival microvascular blood flow was altered in septic patients. In the 24-h observation period conjunctival small vessels had a significantly higher MFI, but no difference in retinal arteriolar diameter in survivors in comparison with non-survivors. Trial registration NCT04214743, https://www.clinicaltrials.gov. Date of registration: 31 December 2019 – Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04214743
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Affiliation(s)
- Jurate Simkiene
- Department of Intensive Care Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, Kaunas, 50009, Lithuania
| | - Zivile Pranskuniene
- Department of Drug Technology and Social Pharmacy, Lithuanian University of Health Sciences, Eiveniu str. 2, Kaunas, 50009, Lithuania.,Institute of Pharmaceutical Technologies, Lithuanian University of Health Sciences, Eiveniu str. 2, Kaunas, 50009, Lithuania
| | - Astra Vitkauskiene
- Department of Laboratory Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, Kaunas, 50009, Lithuania
| | - Vidas Pilvinis
- Department of Intensive Care Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, Kaunas, 50009, Lithuania
| | - E Christiaan Boerma
- Department of Intensive Care Medicine, Medical Center Leeuwarden, Henri Dunantweg 2, 8901 BR, Leeuwarden, The Netherlands
| | - Andrius Pranskunas
- Department of Intensive Care Medicine, Lithuanian University of Health Sciences, Eiveniu str. 2, Kaunas, 50009, Lithuania.
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Akagi T, Uji A, Huang AS, Weinreb RN, Yamada T, Miyata M, Kameda T, Ikeda HO, Tsujikawa A. Conjunctival and Intrascleral Vasculatures Assessed Using Anterior Segment Optical Coherence Tomography Angiography in Normal Eyes. Am J Ophthalmol 2018; 196:1-9. [PMID: 30099035 DOI: 10.1016/j.ajo.2018.08.009] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Revised: 08/03/2018] [Accepted: 08/03/2018] [Indexed: 01/05/2023]
Abstract
PURPOSE To investigate conjunctival and intrascleral vasculatures using anterior segment optical coherence tomography angiography (AS-OCTA) in normal eyes. DESIGN Cross-sectional study. METHODS AS-OCTA images of the corneal limbus were acquired circumferentially using a swept-source optical coherence tomography system in 10 eyes of 10 healthy subjects. AS-OCTA flow patterns with en face maximum projection were compared between the superficial (from the conjunctival epithelium to a depth of 200 μm) and deep (from a depth of 200 μm to 1000 μm) layers. The OCTA images were also compared with fluorescein scleral angiography and indocyanine green aqueous angiography images. Quantitative parameters (vessel density, vessel length density, vessel diameter index, and fractal dimension) were compared among different locations. RESULTS The OCTA vessel patterns differed between the superficial and deep layers. The superficial-layer flow signals showed centrifugal patterns from the limbus, whereas the deep-layer flow signals showed segmental patterns. The OCTA en face images with whole signals had a similar appearance to the scleral angiography images, whereas those in the deep layer showed a similar appearance to the aqueous angiography images. In the superficial layer, only the vessel diameter index was significantly different among the locations (P = .003). In the deep layer, all 4 parameters differed significantly among the locations (P < .001 to P = .003). CONCLUSIONS OCTA is a promising tool for evaluating conjunctival and intrascleral vasculatures. It may also help in understanding ocular surface blood flow relevant to vascular and ocular surface diseases, as well as aqueous humor outflow.
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Khansari MM, Tan M, Karamian P, Shahidi M. Inter-visit variability of conjunctival microvascular hemodynamic measurements in healthy and diabetic retinopathy subjects. Microvasc Res 2018; 118:7-11. [PMID: 29438814 PMCID: PMC5992619 DOI: 10.1016/j.mvr.2018.01.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 01/12/2018] [Accepted: 01/15/2018] [Indexed: 12/18/2022]
Abstract
Conjunctival microcirculation imaging provides a non-invasive means for detecting hemodynamic alterations due to systemic and ocular diseases. However, reliable longitudinal monitoring of hemodynamic changes due to disease progression requires establishment of measurement variability over time. The purpose of the current study was to determine inter-visit variability of conjunctival microvascular hemodynamic measurements in non-diabetic control (NC, N = 7) and diabetic retinopathy (DR, N = 10) subjects. Conjunctival microvascular imaging was performed during 2 visits, which were 17 ± 12 weeks apart. Images were analyzed to determine vessel diameter (D), axial blood velocity (V), blood flow (Q), wall shear rate (WSR) and wall shear stress (WSS). The inter-visit variability was determined based on mean inter-visit differences. In NC, inter-visit variability of D, V, Q, WSR and WSS were 0.2 ± 0.5 µm, −0.01 ± 0.16 mm/s, −8 ± 46 pl/s, −3 ± 46 s−1 and −0.01 ± 0.10 dyne/cm2, respectively. Inter-visit variability of D, V, Q, WSR and WSS were beyond the normal 95% confidence limits in 60%, 20%, 40%, 20% and 20% of DR subjects, respectively. The variability of hemodynamic measurements over time was established in non-diabetic subjects, suggestive of the potential of the method for detecting longitudinal changes due to progression of DR.
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Affiliation(s)
- Maziyar M Khansari
- Department of Ophthalmology, University of Southern California, CA, USA; Laboratory of Neuro Imaging, USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, CA, USA
| | - Michael Tan
- Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, IL, USA
| | - Preny Karamian
- Department of Ophthalmology, University of Southern California, CA, USA
| | - Mahnaz Shahidi
- Department of Ophthalmology, University of Southern California, CA, USA.
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Affiliation(s)
- Lewis. E. MacKenzie
- School of Biomedical Sciences, University of Leeds, Garstang Building Leeds, Leeds, UK
| | - Andy. R. Harvey
- School of Physics and Astronomy, Kelvin Building University of Glasgow University Avenue, Glasgow, UK
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Felder AE, Mercurio C, Wanek J, Ansari R, Shahidi M. Automated Real-Time Conjunctival Microvasculature Image Stabilization. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:1670-1675. [PMID: 26863649 PMCID: PMC5745197 DOI: 10.1109/tmi.2016.2522918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The bulbar conjunctiva is a thin, vascularized membrane covering the sclera of the eye. Non-invasive imaging techniques have been utilized to assess the conjunctival vasculature as a means of studying microcirculatory hemodynamics. However, eye motion often confounds quantification of these hemodynamic properties. In the current study, we present a novel optical imaging system for automated stabilization of conjunctival microvasculature images by real-time eye motion tracking and realignment of the optical path. The ability of the system to stabilize conjunctival images acquired over time by reducing image displacements and maintaining the imaging area was demonstrated.
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MacKenzie LE, Choudhary TR, McNaught AI, Harvey AR. In vivo oximetry of human bulbar conjunctival and episcleral microvasculature using snapshot multispectral imaging. Exp Eye Res 2016; 149:48-58. [PMID: 27317046 DOI: 10.1016/j.exer.2016.06.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Revised: 05/11/2016] [Accepted: 06/13/2016] [Indexed: 10/21/2022]
Abstract
Multispectral imaging (MSI) is a well-established technique for non-invasive oximetry of retinal blood vessels, which has contributed to the understanding of a variety of retinal conditions, including glaucoma, diabetes, vessel occlusion, and retinal auto-regulation. We report the first study to use snapshot multi-spectral imaging (SMSI) for oximetry of the bulbar conjunctival and episcleral microvasculature in the anterior segment of the eye. We report the oxygen dynamics of the bulbar conjunctival and episcleral microvasculature at normoxia and at acute mild hypoxia conditions. A retinal-fundus camera fitted with a custom Image-Replicating Imaging Spectrometer was used to image the bulbar conjunctival and episcleral microvasculature in ten healthy human subjects at normoxia (21% Fraction of Inspired Oxygen [FiO2]) and acute mild hypoxia (15% FiO2) conditions. Eyelid closure was used to control oxygen diffusion between ambient air and the sclera surface. Four subjects were imaged for 30 seconds immediately following eyelid opening. Vessel diameter and Optical Density Ratio (ODR: a direct proxy for oxygen saturation) of vessels was computed automatically. Oximetry capability was validated using a simple phantom that mimicked the scleral vasculature. Acute mild hypoxia resulted in a decrease in blood oxygen saturation (SO2) (i.e. an increase in ODR) when compared with normoxia in both bulbar conjunctival (p < 0.001) and episcleral vessels (p = 0.03). Average episcleral diameter increased from 78.9 ± 8.7 μm (mean ± standard deviation) at normoxia to 97.6 ± 14.3 μm at hypoxia (p = 0.02). Diameters of bulbar conjunctival vessels showed no significant change from 80.1 ± 7.6 μm at normoxia to 80.6 ± 7.0 μm at hypoxia (p = 0.89). When exposed to ambient air, hypoxic bulbar conjunctival vessels rapidly reoxygenated due to oxygen diffusion from ambient air. Reoxygenation occured in an exponential manner, and SO2 reached normoxia baseline levels. The average ½ time to full reoxygenation was 3.4 ± 1.4 s. As a consequence of oxygen diffusion, bulbar conjunctival vessels will be highly oxygenated (i.e. close to 100% SO2) when exposed to ambient air. Episcleral vessels were not observed to undergo any significant oxygen diffusion, instead behaving similarly to pulse oximetry measurements. This is the first study to the image oxygen dynamics of bulbar conjunctival and episcleral microvasculature, and consequently, the first study to directly observe the rapid reoxygenation of hypoxic bulbar conjunctival vessels when exposed to ambient air. Oximetry of bulbar conjunctival vessels could potentially provide insight into conditions where oxygen dynamics of the microvasculature are not fully understood, such as diabetes, sickle-cell diseases, and dry-eye syndrome. Oximetry in the bulbar conjunctival and episcleral microvasculature could be complimentary or alternative to retinal oximetry.
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Affiliation(s)
- L E MacKenzie
- School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom
| | - T R Choudhary
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom; EPSRC IRC "Hub" in Optical Molecular Sensing & Imaging, MRC Centre for Inflammation Research, Queen's Medical Research Institute, University of Edinburgh, Edinburgh, United Kingdom
| | - A I McNaught
- Department of Ophthalmology, Cheltenham General Hospital, Gloucestershire Hospitals NHS Foundation Trust, Gloucestershire, United Kingdom; School of Health Professions, Plymouth University, Plymouth, United Kingdom
| | - A R Harvey
- School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom.
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Khansari MM, Wanek J, Felder AE, Camardo N, Shahidi M. Automated Assessment of Hemodynamics in the Conjunctival Microvasculature Network. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:605-11. [PMID: 26452274 PMCID: PMC4821773 DOI: 10.1109/tmi.2015.2486619] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The conjunctival microcirculation is accessible for direct visualization and quantitative assessment of microvascular hemodynamic properties. Currently available methods to assess hemodynamics in the conjunctival microvasculature use manual or semi-automated algorithms, which can be inefficient for application to a large number of microvessels within the microvascular network. We present an automated image analysis method for measurements of diameter and blood velocity in microvessels. The method was applied to conjunctival microcirculation images acquired in 15 healthy human subjects. Frangi filtering, thresholding, and morphological closing were applied to automatically segment microvessels, while variance filtering was used to detect blood flow. Diameter and blood velocity were measured in arterioles and venules within the conjunctival microvascular network, and blood flow and wall shear rate were calculated. Repeatability and validity of hemodynamic measurements were established. The automated image analysis method allows reliable, rapid and quantitative assessment of hemodynamics in the conjunctival microvascular network and can be potentially applied to microcirculation images of other tissues.
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Affiliation(s)
- Maziyar M. Khansari
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Justin Wanek
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Anthony E. Felder
- Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Nicole Camardo
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Mahnaz Shahidi
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, IL, 60612, USA
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