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Merkle CW, Augustin M, Harper DJ, Glösmann M, Baumann B. Degeneration of Melanin-Containing Structures Observed Longitudinally in the Eyes of SOD1-/- Mice Using Intensity, Polarization, and Spectroscopic OCT. Transl Vis Sci Technol 2022; 11:28. [PMID: 36259678 PMCID: PMC9587514 DOI: 10.1167/tvst.11.10.28] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Purpose Melanin plays an important function in maintaining eye health, however there are few metrics that can be used to study retinal melanin content in vivo. Methods The slope of the spectral coefficient of variation (SSCoV) is a novel biomarker that measures chromophore concentration by analyzing the local divergence of spectral intensities using optical coherence tomography (OCT). This metric was validated in a phantom and applied in a longitudinal study of superoxide dismutase 1 knockout (SOD1−/−) mice, a model for wet and dry age-related macular degeneration. We also examined a new feature of interest in standard OCT image data, the ratio of maximum intensity in the retinal pigment epithelium to that of the choroid (RC ratio). These new biomarkers were supported by polarization-sensitive OCT and histological analysis. Results SSCoV correlated well with depolarization metrics both in phantom and in vivo with both metrics decreasing more rapidly in SOD1−/− mice with age (P < 0.05). This finding is correlated with reduced melanin pigmentation in the choroid over time. The RC ratio clearly differentiated the SOD1−/− and control groups (P < 0.0005) irrespective of time and may indicate lower retinal pigment epithelium melanin in the SOD1−/− mice. Histological analysis showed decreased melanin content and potential differences in melanin granule shape in SOD1−/− mice. Conclusions SSCoV and RC ratio biomarkers provided insights into the changes of retinal melanin in the SOD1−/− model longitudinally and noninvasively. Translational Relevance These biomarkers were designed with the potential for rapid adoption by existing clinical OCT systems without requiring new hardware.
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Affiliation(s)
- Conrad W Merkle
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Marco Augustin
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Danielle J Harper
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Martin Glösmann
- Core Facility for Research and Technology, University of Veterinary Medicine Vienna, Austria
| | - Bernhard Baumann
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
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2
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Baumann B, Merkle CW, Augustin M, Glösmann M, Garhöfer G. Pulsatile tissue deformation dynamics of the murine retina and choroid mapped by 4D optical coherence tomography. Biomed Opt Express 2022; 13:647-661. [PMID: 35284183 PMCID: PMC8884196 DOI: 10.1364/boe.445093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 12/20/2021] [Accepted: 12/28/2021] [Indexed: 05/11/2023]
Abstract
Irregular ocular pulsatility and altered mechanical tissue properties are associated with some of the most sight-threatening eye diseases. Here we present 4D optical coherence tomography (OCT) for the quantitative assessment and depth-resolved mapping of pulsatile dynamics in the murine retina and choroid. Through a pixel-wise analysis of phase changes of the complex OCT signal, we reveal spatiotemporal displacement characteristics across repeated frame acquisitions. We demonstrate in vivo fundus elastography (FUEL) imaging in wildtype mouse retinas and in a mouse model of retinal neovascularization and uncover subtle structural deformations related to ocular pulsation. Our data in mouse eyes hold promise for a powerful retinal elastography technique that may enable a new paradigm of OCT-based measurements and image contrast.
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Affiliation(s)
- Bernhard Baumann
- Center for Medical Physics and Biomedical
Engineering, Medical University of Vienna,
Währinger Gürtel 18-20, 1090 Vienna, Austria
| | - Conrad W. Merkle
- Center for Medical Physics and Biomedical
Engineering, Medical University of Vienna,
Währinger Gürtel 18-20, 1090 Vienna, Austria
| | - Marco Augustin
- Center for Medical Physics and Biomedical
Engineering, Medical University of Vienna,
Währinger Gürtel 18-20, 1090 Vienna, Austria
| | - Martin Glösmann
- Core Facility for Research and Technology,
University of Veterinary Medicine Vienna,
Veterinärplatz 1, 1210 Vienna, Austria
| | - Gerhard Garhöfer
- Department of Clinical Pharmacology,
Medical University of Vienna, Währinger
Gürtel 18-20, 1090 Vienna, Austria
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3
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Eugui P, Merkle CW, Gesperger J, Lichtenegger A, Baumann B. Investigation of the scattering and attenuation properties of cataracts formed in mouse eyes with 1060-nm and 1310-nm swept-source optical coherence tomography. Biomed Opt Express 2021; 12:6391-6406. [PMID: 34745744 PMCID: PMC8547986 DOI: 10.1364/boe.433927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 08/31/2021] [Accepted: 08/31/2021] [Indexed: 06/13/2023]
Abstract
Cataracts are the leading cause of blindness worldwide. Here we propose optical coherence tomography (OCT) as a quantitative method for investigating cataracts. OCT provides volumetric and non-invasive access to the lens and makes it possible to rapidly observe the formation of opacifications in animal models such as mice. We compared the performance of two different wavelengths - 1060 nm and 1310 nm - for OCT imaging in cataract research. In addition, we present multi-contrast OCT capable of mapping depth-resolved scattering and average anterior cortical attenuation properties of the crystalline lens and quantitatively characterize induced cataract development in the mouse eye. Lastly, we also propose a novel method based on the retinal OCT projection image for quantifying and mapping opacifications in the lens, which showed a good correlation with scattering and attenuation characteristics simultaneously analyzed during the process of cataract formation in the lens.
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Affiliation(s)
- Pablo Eugui
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Conrad W. Merkle
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Johanna Gesperger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
- Division of Neuropathology and Neurochemistry, Department of Neurology, Medical University of Vienna, Austria
| | - Antonia Lichtenegger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Bernhard Baumann
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
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4
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Baumann B, Harper DJ, Eugui P, Gesperger J, Lichtenegger A, Merkle CW, Augustin M, Woehrer A. Improved accuracy of quantitative birefringence imaging by polarization sensitive OCT with simple noise correction and its application to neuroimaging. J Biophotonics 2021; 14:e202000323. [PMID: 33332741 DOI: 10.1002/jbio.202000323] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 12/13/2020] [Accepted: 12/14/2020] [Indexed: 05/25/2023]
Abstract
Polarization-sensitive optical coherence tomography (PS-OCT) enables three-dimensional imaging of biological tissues based on the inherent contrast provided by scattering and polarization properties. In fibrous tissue such as the white matter of the brain, PS-OCT allows quantitative mapping of tissue birefringence. For the popular PS-OCT layout using a single circular input state, birefringence measurements are based on a straight-forward evaluation of phase retardation data. However, the accuracy of these measurements strongly depends on the signal-to-noise ratio (SNR) and is prone to mapping artifacts when the SNR is low. Here we present a simple yet effective approach for improving the accuracy of PS-OCT phase retardation and birefringence measurements. By performing a noise bias correction of the detected OCT signal amplitudes, the impact of the noise floor on retardation measurements can be markedly reduced. We present simulation data to illustrate the influence of the noise bias correction on phase retardation measurements and support our analysis with real-world PS-OCT image data.
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Affiliation(s)
- Bernhard Baumann
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Danielle J Harper
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Pablo Eugui
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Johanna Gesperger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
- Division of Neuropathology and Neurochemistry, Department of Neurology, Medical University of Vienna, Vienna, Austria
| | - Antonia Lichtenegger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Conrad W Merkle
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Marco Augustin
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Adelheid Woehrer
- Division of Neuropathology and Neurochemistry, Department of Neurology, Medical University of Vienna, Vienna, Austria
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5
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Merkle CW, Augustin M, Harper DJ, Gesperger J, Lichtenegger A, Eugui P, Garhöfer G, Glösmann M, Baumann B. High-resolution, depth-resolved vascular leakage measurements using contrast-enhanced, correlation-gated optical coherence tomography in mice. Biomed Opt Express 2021; 12:1774-1791. [PMID: 33996197 PMCID: PMC8086440 DOI: 10.1364/boe.415227] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 01/22/2021] [Accepted: 01/24/2021] [Indexed: 06/09/2023]
Abstract
Vascular leakage plays a key role in vision-threatening retinal diseases such as diabetic retinopathy and age-related macular degeneration. Fluorescence angiography is the current gold standard for identification of leaky vasculature in vivo, however it lacks depth resolution, providing only 2D images that complicate precise identification and localization of pathological vessels. Optical coherence tomography (OCT) has been widely adopted for clinical ophthalmology due to its high, micron-scale resolution and rapid volumetric scanning capabilities. Nevertheless, OCT cannot currently identify leaky blood vessels. To address this need, we have developed a new method called exogenous contrast-enhanced leakage OCT (ExCEL-OCT) which identifies the diffusion of tracer particles around leaky vasculature following injection of a contrast agent. We apply this method to a mouse model of retinal neovascularization and demonstrate high-resolution 3D vascular leakage measurements in vivo for the first time.
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Affiliation(s)
- Conrad W. Merkle
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Marco Augustin
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Danielle J. Harper
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Johanna Gesperger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
- Division of Neuropathology and Neurochemistry, Department of Neurology, Medical University of Vienna, Vienna, Austria
| | - Antonia Lichtenegger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Pablo Eugui
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Gerhard Garhöfer
- Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Martin Glösmann
- Core Facility for Research and Technology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Bernhard Baumann
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
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6
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Kho AM, Zhang T, Zhu J, Merkle CW, Srinivasan VJ. Incoherent excess noise spectrally encodes broadband light sources. Light Sci Appl 2020; 9:172. [PMID: 33082941 PMCID: PMC7538909 DOI: 10.1038/s41377-020-00404-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 08/26/2020] [Accepted: 09/09/2020] [Indexed: 05/09/2023]
Abstract
Across optics and photonics, excess intensity noise is often considered a liability. Here, we show that excess noise in broadband supercontinuum and superluminescent diode light sources encodes each spectral channel with unique intensity fluctuations, which actually serve a useful purpose. Specifically, we report that excess noise correlations can both characterize the spectral resolution of spectrometers and enable cross-calibration of their wavelengths across a broad bandwidth. Relative to previous methods that use broadband interferometry and narrow linewidth lasers to characterize and calibrate spectrometers, our approach is simple, comprehensive, and rapid enough to be deployed during spectrometer alignment. First, we employ this approach to aid alignment and reduce the depth-dependent degradation of the sensitivity and axial resolution in a spectrometer-based optical coherence tomography (OCT) system, revealing a new outer retinal band. Second, we achieve a pixel-to-pixel correspondence between two otherwise disparate spectrometers, enabling a robust comparison of their respective measurements. Thus, excess intensity noise has useful applications in optics and photonics.
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Affiliation(s)
- Aaron M. Kho
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616 USA
| | - Tingwei Zhang
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616 USA
| | - Jun Zhu
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616 USA
| | - Conrad W. Merkle
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616 USA
| | - Vivek J. Srinivasan
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616 USA
- Department of Ophthalmology and Vision Science, University of California Davis School of Medicine, Sacramento, CA 95817 USA
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7
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Zhu J, Bernucci MT, Merkle CW, Srinivasan VJ. Visibility of microvessels in Optical Coherence Tomography angiography depends on angular orientation. J Biophotonics 2020; 13:e202000090. [PMID: 32468737 PMCID: PMC7737355 DOI: 10.1002/jbio.202000090] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 05/20/2020] [Accepted: 05/21/2020] [Indexed: 05/02/2023]
Abstract
Optical Coherence Tomography angiography (OCTA) is a widespread tool for depth-resolved imaging of chorioretinal vasculature with single microvessel resolution. To improve the clinical interpretation of OCTA, the conditions affecting visualization of microvessels must be defined. Here we inject a scattering plasma tracer (Intralipid) during OCTA imaging of the anesthetized rat eye. In the retina, we find that interlaminar (vertical) vessels that connect laminae have one-fourth to one-third the OCTA red blood cell to tracer (RBC-to-tracer) signal ratio of intralaminar (horizontal) vessels. This finding suggests that the OCTA signal from microvessels depends on angular orientation, making vertically-oriented vessels more difficult to visualize using intrinsic contrast alone. Clinicians should be aware of this potential artifact when interpreting OCTA.
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Affiliation(s)
- Jun Zhu
- Biomedical Engineering Department, University of California Davis, Davis, California
| | - Marcel T. Bernucci
- Biomedical Engineering Department, University of California Davis, Davis, California
| | - Conrad W. Merkle
- Biomedical Engineering Department, University of California Davis, Davis, California
| | - Vivek J. Srinivasan
- Biomedical Engineering Department, University of California Davis, Davis, California
- Department of Ophthalmology and Vision Science, University of California Davis School of Medicine, Sacramento, California
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8
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Gesperger J, Lichtenegger A, Roetzer T, Salas M, Eugui P, Harper DJ, Merkle CW, Augustin M, Kiesel B, Mercea PA, Widhalm G, Baumann B, Woehrer A. Improved Diagnostic Imaging of Brain Tumors by Multimodal Microscopy and Deep Learning. Cancers (Basel) 2020; 12:E1806. [PMID: 32640583 PMCID: PMC7408054 DOI: 10.3390/cancers12071806] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 06/26/2020] [Accepted: 07/01/2020] [Indexed: 11/16/2022] Open
Abstract
Fluorescence-guided surgery is a state-of-the-art approach for intraoperative imaging during neurosurgical removal of tumor tissue. While the visualization of high-grade gliomas is reliable, lower grade glioma often lack visible fluorescence signals. Here, we present a hybrid prototype combining visible light optical coherence microscopy (OCM) and high-resolution fluorescence imaging for assessment of brain tumor samples acquired by 5-aminolevulinic acid (5-ALA) fluorescence-guided surgery. OCM provides high-resolution information of the inherent tissue scattering and absorption properties of tissue. We here explore quantitative attenuation coefficients derived from volumetric OCM intensity data and quantitative high-resolution 5-ALA fluorescence as potential biomarkers for tissue malignancy including otherwise difficult-to-assess low-grade glioma. We validate our findings against the gold standard histology and use attenuation and fluorescence intensity measures to differentiate between tumor core, infiltrative zone and adjacent brain tissue. Using large field-of-view scans acquired by a near-infrared swept-source optical coherence tomography setup, we provide initial assessments of tumor heterogeneity. Finally, we use cross-sectional OCM images to train a convolutional neural network that discriminates tumor from non-tumor tissue with an accuracy of 97%. Collectively, the present hybrid approach offers potential to translate into an in vivo imaging setup for substantially improved intraoperative guidance of brain tumor surgeries.
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Affiliation(s)
- Johanna Gesperger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
- Division of Neuropathology and Neurochemistry, Department of Neurology, Medical University of Vienna, 1090 Vienna, Austria; (T.R.); (A.W.)
| | - Antonia Lichtenegger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
| | - Thomas Roetzer
- Division of Neuropathology and Neurochemistry, Department of Neurology, Medical University of Vienna, 1090 Vienna, Austria; (T.R.); (A.W.)
| | - Matthias Salas
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
| | - Pablo Eugui
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
| | - Danielle J. Harper
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
| | - Conrad W. Merkle
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
| | - Marco Augustin
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
| | - Barbara Kiesel
- Department of Neurosurgery, Medical University of Vienna, 1090 Vienna, Austria; (B.K.); (P.A.M.)
| | - Petra A. Mercea
- Department of Neurosurgery, Medical University of Vienna, 1090 Vienna, Austria; (B.K.); (P.A.M.)
| | - Georg Widhalm
- Department of Neurosurgery, Medical University of Vienna, 1090 Vienna, Austria; (B.K.); (P.A.M.)
| | - Bernhard Baumann
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, 1090 Vienna, Austria; (J.G.); (A.L.); (M.S.); (P.E.); (D.J.H.); (C.W.M.); (M.A.)
| | - Adelheid Woehrer
- Division of Neuropathology and Neurochemistry, Department of Neurology, Medical University of Vienna, 1090 Vienna, Austria; (T.R.); (A.W.)
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9
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Merkle CW, Augustin M, Harper DJ, Baumann B. Indocyanine green provides absorption and spectral contrast for optical coherence tomography at 840 nm in vivo. Opt Lett 2020; 45:2359-2362. [PMID: 32287239 DOI: 10.1364/ol.380051] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Accepted: 01/10/2020] [Indexed: 05/25/2023]
Abstract
In recent years, there has been growing interest in the application of exogenous contrast agents to supplement the traditional strengths of optical coherence tomography (OCT) and provide additional biological information. In this Letter, we present how indocyanine green, a common fluorescent contrast agent approved by the United States Food and Drug Administration, can provide absorption and spectral contrast for OCT imaging in the mouse eye in vivo. We further demonstrate high stability of spectral contrast measurements for the long-term monitoring of contrast agents in spite of fluctuations in intensity.
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10
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Eugui P, Harper DJ, Kummer S, Lichtenegger A, Gesperger J, Himmel T, Augustin M, Merkle CW, Glösmann M, Baumann B. Three-dimensional visualization of opacifications in the murine crystalline lens by in vivo optical coherence tomography. Biomed Opt Express 2020; 11:2085-2097. [PMID: 32341868 PMCID: PMC7173898 DOI: 10.1364/boe.387335] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 03/05/2020] [Accepted: 03/12/2020] [Indexed: 05/03/2023]
Abstract
Diagnostic classification techniques used to diagnose cataracts, the world's leading cause of blindness, are currently based on subjective methods. Here, we present optical coherence tomography as a noninvasive tool for volumetric visualization of lesions formed in the crystalline lens. A custom-made swept-source optical coherence tomography (SS-OCT) system was utilized to investigate the murine crystalline lens. In addition to imaging cataractous lesions in aged wildtype mice, we studied the structure and shape of cataracts in a mouse model of Alzheimer's disease. Hyperscattering opacifications in the crystalline lens were observed in both groups. Post mortem histological analysis were performed to correlate findings in the anterior and posterior part of the lens to 3D OCT in vivo imaging. Our results showcase the capability of OCT to rapidly visualize cataractous lesions in the murine lens and suggest that OCT might be a valuable tool that provides additional insight for preclinical studies of cataract formation.
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Affiliation(s)
- Pablo Eugui
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Danielle J. Harper
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Stefan Kummer
- Core Facility for Research and Technology, University of Veterinary Medicine, Austria
| | - Antonia Lichtenegger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Johanna Gesperger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
- Division of Neuropathology and Neurochemistry, Department of Neurology of the Medical University of Vienna, Austria
| | - Tanja Himmel
- Core Facility for Research and Technology, University of Veterinary Medicine, Austria
| | - Marco Augustin
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Conrad W. Merkle
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
| | - Martin Glösmann
- Core Facility for Research and Technology, University of Veterinary Medicine, Austria
| | - Bernhard Baumann
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria
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11
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Augustin M, Harper DJ, Merkle CW, Glösmann M, Hitzenberger CK, Baumann B. Optical Coherence Tomography Findings in the Retinas of SOD1 Knockout Mice. Transl Vis Sci Technol 2020; 9:15. [PMID: 32818102 PMCID: PMC7396182 DOI: 10.1167/tvst.9.4.15] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Accepted: 12/16/2019] [Indexed: 01/22/2023] Open
Abstract
Purpose The retinal phenotype of popular mouse models mimicking ophthalmic diseases, such as the superoxide dismutase 1 (SOD1) knockout (KO) mouse model, has mainly been assessed by ex vivo histology and in vivo fundus photography. We used multifunctional optical coherence tomography (OCT) to characterize the retinas of SOD1 KO mice in vivo. Methods The custom-made ophthalmoscope featured a combination of conventional OCT, polarization-sensitive OCT, and OCT angiography. Seven SOD1 KO mice and nine age-matched controls were imaged between 6 and 17 months of age. A postprocessing framework was used to analyze total and outer retinal thickness changes. Drusenlike lesions were segmented, and their sizes and the number of lesions were assessed quantitatively. Their appearance in the conventional reflectivity images, as well as in the corresponding polarization-sensitive images, was characterized qualitatively. Results Drusenlike lesions increased in size and number with age for SOD1 KO mice. Exploiting the multiple contrast channels, the appearance of the lesions was found to resemble pseudodrusen observed in eyes of patients suffering from dry age-related macular degeneration. The total and outer retinal thicknesses were lower on average after 11 months and 7 months in SOD1 KO mice compared with age-matched controls. Neovascularizations were found in one out of seven KO animals. Conclusions OCT imaging proved beneficial for a detailed in vivo characterization of the pathological changes in SOD1 KO mice. Translational Relevance Phenotyping of animal models using modern imaging concepts can be conducted with more precision and might also ease the translation of conclusions between clinical and preclinical research.
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Affiliation(s)
- Marco Augustin
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Danielle J Harper
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Conrad W Merkle
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Martin Glösmann
- VetCore Facility for Research, Imaging Unit, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Christoph K Hitzenberger
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Bernhard Baumann
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
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12
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Eugui P, Danielle JH, Gesperger J, Lichtenegger A, Merkle CW, Glösmann M, Baumann B. Attenuation coefficient as a quantitative parameter for analyzing cataracts with optical coherence tomography. EPJ Web Conf 2020. [DOI: 10.1051/epjconf/202023804004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Crystalline lenses of mice were imaged in vivo with a custom-made swept-source optical coherence tomography system. The use of the attenuation coefficient as a quantitative parameter for investigating the lens opacities magnitude is proposed, demonstrating a significant difference between the values retrieved from cataractous and normal mouse lenses.
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13
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Harper DJ, Augustin M, Lichtenegger A, Gesperger J, Himmel T, Muck M, Merkle CW, Eugui P, Kummer S, Woehrer A, Glösmann M, Baumann B. Retinal analysis of a mouse model of Alzheimer's disease with multicontrast optical coherence tomography. Neurophotonics 2020; 7:015006. [PMID: 32042855 PMCID: PMC6999077 DOI: 10.1117/1.nph.7.1.015006] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 01/07/2020] [Indexed: 05/18/2023]
Abstract
Significance. Recent Alzheimer's disease (AD) patient studies have focused on retinal analysis, as the retina is the only part of the central nervous system that can be imaged noninvasively by optical methods. However, as this is a relatively new approach, the occurrence and role of retinal pathological features are still debated. Aim. The retina of an APP/PS1 mouse model was investigated using multicontrast optical coherence tomography (OCT) in order to provide a documentation of what was observed in both transgenic and wild-type mice. Approach. Both eyes of 24 APP/PS1 transgenic mice (age: 45 to 104 weeks) and 15 age-matched wild-type littermates were imaged by the custom-built OCT system. At the end of the experiment, retinas and brains were harvested from a subset of the mice (14 transgenic, 7 age-matched control) in order to compare the in vivo results to histological analysis and to quantify the cortical amyloid beta plaque load. Results. The system provided a combination of standard reflectivity data, polarization-sensitive data, and OCT angiograms. Qualitative and quantitative information from the resultant OCT images was extracted on retinal layer thickness and structure, presence of hyper-reflective foci, phase retardation abnormalities, and retinal vasculature. Conclusions. Although multicontrast OCT revealed abnormal structural properties and phase retardation signals in the retina of this APP/PS1 mouse model, the observations were very similar in transgenic and control mice.
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Affiliation(s)
- Danielle J. Harper
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
- Address all correspondence to Danielle J. Harper, E-mail:
| | - Marco Augustin
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Antonia Lichtenegger
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Johanna Gesperger
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
- General Hospital and Medical University of Vienna, Institute of Neurology, Vienna, Austria
| | - Tanja Himmel
- University of Veterinary Medicine, Institute of Pathology, Vienna, Austria
| | - Martina Muck
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Conrad W. Merkle
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Pablo Eugui
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Stefan Kummer
- University of Veterinary Medicine, Core Facility for Research and Technology, Vienna, Austria
| | - Adelheid Woehrer
- General Hospital and Medical University of Vienna, Institute of Neurology, Vienna, Austria
| | - Martin Glösmann
- University of Veterinary Medicine, Core Facility for Research and Technology, Vienna, Austria
| | - Bernhard Baumann
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
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14
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Harper DJ, Konegger T, Augustin M, Schützenberger K, Eugui P, Lichtenegger A, Merkle CW, Hitzenberger CK, Glösmann M, Baumann B. Hyperspectral optical coherence tomography for in vivo visualization of melanin in the retinal pigment epithelium. J Biophotonics 2019; 12:e201900153. [PMID: 31334610 PMCID: PMC7065636 DOI: 10.1002/jbio.201900153] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 06/19/2019] [Accepted: 07/18/2019] [Indexed: 05/09/2023]
Abstract
Previous studies for melanin visualization in the retinal pigment epithelium (RPE) have exploited either its absorption properties (using photoacoustic tomography or photothermal optical coherence tomography [OCT]) or its depolarization properties (using polarization sensitive OCT). However, these methods are only suitable when the melanin concentration is sufficiently high. In this work, we present the concept of hyperspectral OCT for melanin visualization in the RPE when the concentration is low. Based on white light OCT, a hyperspectral stack of 27 wavelengths (440-700 nm) was created in post-processing for each depth-resolved image. Owing to the size and shape of the melanin granules in the RPE, the variations in backscattering coefficient as a function of wavelength could be identified-a result which is to be expected from Mie theory. This effect was successfully identified both in eumelanin-containing phantoms and in vivo in the low-concentration Brown Norway rat RPE.
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Affiliation(s)
- Danielle J. Harper
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | - Thomas Konegger
- Institute of Chemical Technologies and Analytics, TU WienViennaAustria
| | - Marco Augustin
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | - Kornelia Schützenberger
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | - Pablo Eugui
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | - Antonia Lichtenegger
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | - Conrad W. Merkle
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | | | - Martin Glösmann
- Core Facility for Research and TechnologyUniversity of Veterinary MedicineViennaAustria
| | - Bernhard Baumann
- Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
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15
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Baumann B, Merkle CW, Leitgeb RA, Augustin M, Wartak A, Pircher M, Hitzenberger CK. Signal averaging improves signal-to-noise in OCT images: But which approach works best, and when? Biomed Opt Express 2019; 10:5755-5775. [PMID: 31799045 PMCID: PMC6865101 DOI: 10.1364/boe.10.005755] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 09/04/2019] [Accepted: 09/26/2019] [Indexed: 05/22/2023]
Abstract
The high acquisition speed of state-of-the-art optical coherence tomography (OCT) enables massive signal-to-noise ratio (SNR) improvements by signal averaging. Here, we investigate the performance of two commonly used approaches for OCT signal averaging. We present the theoretical SNR performance of (a) computing the average of OCT magnitude data and (b) averaging the complex phasors, and substantiate our findings with simulations and experimentally acquired OCT data. We show that the achieved SNR performance strongly depends on both the SNR of the input signals and the number of averaged signals when the signal bias caused by the noise floor is not accounted for. Therefore we also explore the SNR for the two averaging approaches after correcting for the noise bias and, provided that the phases of the phasors are accurately aligned prior to averaging, then find that complex phasor averaging always leads to higher SNR than magnitude averaging.
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16
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Eugui P, Harper DJ, Lichtenegger A, Augustin M, Merkle CW, Woehrer A, Hitzenberger CK, Baumann B. Polarization-sensitive imaging with simultaneous bright- and dark-field optical coherence tomography. Opt Lett 2019; 44:4040-4043. [PMID: 31415542 DOI: 10.1364/ol.44.004040] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 07/04/2019] [Indexed: 05/20/2023]
Abstract
We present a polarization-sensitive (PS) extension for bright- and dark-field (BRAD) optical coherence tomography imaging. Using a few-mode fiber detection scheme, the light backscattered at different angles is separated, and the BRAD images of tissue scattering are generated. A calibration method to correct for the fiber birefringence is proposed. Since particle scattering profiles are polarization dependent, a PS detection extends the capabilities for investigating the scattering properties of biological tissues. Both phantoms consisting of different-sized microparticles and a brain tissue specimen were imaged to validate the system performance and demonstrate the complementary image contrast.
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17
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Merkle CW, Zhu J, Bernucci MT, Srinivasan VJ. Dynamic Contrast Optical Coherence Tomography reveals laminar microvascular hemodynamics in the mouse neocortex in vivo. Neuroimage 2019; 202:116067. [PMID: 31394180 DOI: 10.1016/j.neuroimage.2019.116067] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 07/01/2019] [Accepted: 08/01/2019] [Indexed: 12/18/2022] Open
Abstract
Studies of flow-metabolism coupling often presume that microvessel architecture is a surrogate for blood flow. To test this assumption, we introduce an in vivo Dynamic Contrast Optical Coherence Tomography (DyC-OCT) method to quantify layer-resolved microvascular blood flow and volume across the full depth of the mouse neocortex, where the angioarchitecture has been previously described. First, we cross-validate average DyC-OCT cortical flow against conventional Doppler OCT flow. Next, with laminar DyC-OCT, we discover that layer 4 consistently exhibits the highest microvascular blood flow, approximately two-fold higher than the outer cortical layers. While flow differences between layers are well-explained by microvascular volume and density, flow differences between subjects are better explained by transit time. Finally, from layer-resolved tracer enhancement, we also infer that microvascular hematocrit increases in deep cortical layers, consistent with predictions of plasma skimming. Altogether, our results show that while the cortical blood supply derives mainly from the pial surface, laminar hemodynamics ensure that the energetic needs of individual cortical layers are met. The laminar trends reported here provide data that links predictions based on the cortical angioarchitecture to cerebrovascular physiology in vivo.
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Affiliation(s)
- Conrad W Merkle
- Department of Biomedical Engineering, University of California Davis, Davis, CA, 95616, USA
| | - Jun Zhu
- Department of Biomedical Engineering, University of California Davis, Davis, CA, 95616, USA
| | - Marcel T Bernucci
- Department of Biomedical Engineering, University of California Davis, Davis, CA, 95616, USA
| | - Vivek J Srinivasan
- Department of Biomedical Engineering, University of California Davis, Davis, CA, 95616, USA; Department of Ophthalmology and Vision Science, University of California Davis School of Medicine, Sacramento, CA, 95817, USA.
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18
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Lichtenegger A, Gesperger J, Kiesel B, Muck M, Eugui P, Harper DJ, Salas M, Augustin M, Merkle CW, Hitzenberger CK, Widhalm G, Woehrer A, Baumann B. Revealing brain pathologies with multimodal visible light optical coherence microscopy and fluorescence imaging. J Biomed Opt 2019; 24:1-11. [PMID: 31240898 PMCID: PMC6977170 DOI: 10.1117/1.jbo.24.6.066010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 06/07/2019] [Indexed: 05/28/2023]
Abstract
We present a multimodal visible light optical coherence microscopy (OCM) and fluorescence imaging (FI) setup. Specification and phantom measurements were performed to characterize the system. Two applications in neuroimaging were investigated. First, curcumin-stained brain slices of a mouse model of Alzheimer's disease were examined. Amyloid-beta plaques were identified based on the fluorescence of curcumin, and coregistered morphological images of the brain tissue were provided by the OCM channel. Second, human brain tumor biopsies retrieved intraoperatively were imaged prior to conventional neuropathologic work-up. OCM revealed the three-dimensional structure of the brain parenchyma, and FI added the tumor tissue-specific contrast. Attenuation coefficients computed from the OCM data and the florescence intensity values were analyzed and showed a statistically significant difference for 5-aminolevulinic acid (5-ALA)-positive and -negative brain tissues. OCM findings correlated well with malignant hot spots within brain tumor biopsies upon histopathology. The combination of OCM and FI seems to be a promising optical imaging modality providing complementary contrast for applications in the field of neuroimaging.
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Affiliation(s)
- Antonia Lichtenegger
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Johanna Gesperger
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
- General Hospital and Medical University of Vienna, Institute of Neurology, Vienna, Austria
| | - Barbara Kiesel
- General Hospital and Medical University of Vienna, Univ. Klinik Neurochirurgie, Vienna, Austria
| | - Martina Muck
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
- General Hospital and Medical University of Vienna, Institute of Neurology, Vienna, Austria
| | - Pablo Eugui
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Danielle J. Harper
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Matthias Salas
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Marco Augustin
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Conrad W. Merkle
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Christoph K. Hitzenberger
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
| | - Georg Widhalm
- General Hospital and Medical University of Vienna, Univ. Klinik Neurochirurgie, Vienna, Austria
| | - Adelheid Woehrer
- General Hospital and Medical University of Vienna, Institute of Neurology, Vienna, Austria
| | - Bernhard Baumann
- Medical University of Vienna, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
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19
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Bernucci MT, Merkle CW, Srinivasan VJ. Investigation of artifacts in retinal and choroidal OCT angiography with a contrast agent. Biomed Opt Express 2018; 9:1020-1040. [PMID: 29541501 PMCID: PMC5846511 DOI: 10.1364/boe.9.001020] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 01/22/2018] [Accepted: 01/24/2018] [Indexed: 05/18/2023]
Abstract
Optical coherence tomography angiography (OCTA) has recently emerged for imaging vasculature in clinical ophthalmology. Yet, OCTA images contain artifacts that remain challenging to interpret. To help explain these artifacts, we perform contrast-enhanced OCTA with a custom-designed wide-field ophthalmoscope in rats in vivo. We choose an intravascular contrast agent (Intralipid) with particles that are more isotropically scattering and more symmetrically shaped than red blood cells (RBCs). Then, by examining how OCTA artifacts change after contrast agent injection, we attribute OCTA artifacts to RBC-specific properties. In this work, we investigate retinal and choroidal OCTA in rats with or without melanosomes, both before and after contrast agent injection, at a wavelength at which scattering dominates the image contrast (1300 nm). First, baseline images suggest that high backscattering of choroidal melanosomes accounts for the relatively dark appearance of choroidal vessel lumens in OCTA. Second, Intralipid injection tends to eliminate the hourglass pattern artifact in OCTA images of vessel lumens and highlights vertical capillaries that were previously faint in OCTA, showing that RBC orientation is important in determining OCTA signal. Third, Intralipid injection increases lumen signal without significantly affecting the tails, suggesting that projection artifacts, or tails, are due to RBC multiple scattering. Fourth, Intralipid injection increases the side-to-top signal ratio less in choroidal vessel lumens of pigmented rats, suggesting that melanosome multiple scattering makes the hourglass artifact less prominent. This study provides the first direct experimental in vivo evidence to explain light scattering-related artifacts in OCTA.
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Affiliation(s)
- Marcel T. Bernucci
- Department of Biomedical Engineering, University of California Davis, Davis, California, USA
| | - Conrad W. Merkle
- Department of Biomedical Engineering, University of California Davis, Davis, California, USA
| | - Vivek J. Srinivasan
- Department of Biomedical Engineering, University of California Davis, Davis, California, USA
- Department of Ophthalmology and Vision Science, University of California Davis School of Medicine, Sacramento, California, USA
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20
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Abstract
Optical Coherence Tomography Angiography (OCTA) refers to a powerful class of OCT scanning protocols and algorithms that selectively enhance the imaging of blood vessel lumens, based mainly on the motion and scattering of red blood cells (RBCs). Though OCTA is widely used in clinical and basic science applications for visualization of perfused blood vessels, OCTA is still primarily a qualitative tool. However, more quantitative hemodynamic information would better delineate disease mechanisms, and potentially improve the sensitivity for detecting early stages of disease. Here, we take a broader view of OCTA in the context of microvascular hemodynamics and light scattering. Paying particular attention to the unique challenges presented by capillaries versus larger supplying and draining vessels, we critically assess opportunities and challenges in making OCTA a quantitative tool.
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Affiliation(s)
- Jun Zhu
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, USA
| | - Conrad W. Merkle
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, USA
| | - Marcel T. Bernucci
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, USA
| | - Shau Poh Chong
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, USA
| | - Vivek J. Srinivasan
- Department of Biomedical Engineering, University of California Davis, Davis, CA 95616, USA
- Department of Ophthalmology and Vision Science, School of Medicine, University of California Davis, Sacramento, CA 95817, USA
- Correspondence: ; Tel.: +1-530-752-9277
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21
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Merkle CW, Leahy C, Srinivasan VJ. Dynamic contrast optical coherence tomography images transit time and quantifies microvascular plasma volume and flow in the retina and choriocapillaris. Biomed Opt Express 2016; 7:4289-4312. [PMID: 27867732 PMCID: PMC5102529 DOI: 10.1364/boe.7.004289] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 08/19/2016] [Accepted: 09/16/2016] [Indexed: 05/18/2023]
Abstract
Despite the prevalence of optical imaging techniques to measure hemodynamics in large retinal vessels, quantitative measurements of retinal capillary and choroidal hemodynamics have traditionally been challenging. Here, a new imaging technique called dynamic contrast optical coherence tomography (DyC-OCT) is applied in the rat eye to study microvascular blood flow in individual retinal and choroidal layers in vivo. DyC-OCT is based on imaging the transit of an intravascular tracer dynamically as it passes through the field-of-view. Hemodynamic parameters can be determined through quantitative analysis of tracer kinetics. In addition to enabling depth-resolved transit time, volume, and flow measurements, the injected tracer also enhances OCT angiograms and enables clear visualization of the choriocapillaris, particularly when combined with a post-processing method for vessel enhancement. DyC-OCT complements conventional OCT angiography through quantification of tracer dynamics, similar to fluorescence angiography, but with the important added benefit of laminar resolution.
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Affiliation(s)
- Conrad W. Merkle
- Department of Biomedical Engineering, University of California Davis, Davis, California, USA
| | - Conor Leahy
- Department of Biomedical Engineering, University of California Davis, Davis, California, USA
| | - Vivek J. Srinivasan
- Department of Biomedical Engineering, University of California Davis, Davis, California, USA
- Department of Ophthalmology and Vision Science, University of California Davis School of Medicine, Sacramento, California, USA
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22
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Chong SP, Merkle CW, Cooke DF, Zhang T, Radhakrishnan H, Krubitzer L, Srinivasan VJ. Noninvasive, in vivo imaging of subcortical mouse brain regions with 1.7 μm optical coherence tomography. Opt Lett 2015; 40:4911-4. [PMID: 26512481 PMCID: PMC4871109 DOI: 10.1364/ol.40.004911] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
A spectral/Fourier domain optical coherence tomography (OCT) intravital microscope using a supercontinuum light source at 1.7 μm was developed to study subcortical structures noninvasively in the living mouse brain. The benefits of 1.7 μm for deep tissue brain imaging are demonstrated by quantitatively comparing OCT signal attenuation characteristics of cortical tissue across visible and near-infrared wavelengths. Imaging of hippocampal tissue architecture and white matter microvasculature are demonstrated in vivo through thinned-skull, glass coverslip-reinforced cranial windows in mice. Applications of this novel platform include monitoring disease progression and pathophysiology in rodent models of Alzheimer's disease and subcortical dementias, including vascular dementia.
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Affiliation(s)
- Shau Poh Chong
- Biomedical Engineering Department, University of California Davis, Davis, California 95616, USA
| | - Conrad W. Merkle
- Biomedical Engineering Department, University of California Davis, Davis, California 95616, USA
| | - Dylan F. Cooke
- Department of Psychology & Center for Neuroscience, University of California Davis, Davis, California 95616, USA
| | - Tingwei Zhang
- Biomedical Engineering Department, University of California Davis, Davis, California 95616, USA
| | - Harsha Radhakrishnan
- Biomedical Engineering Department, University of California Davis, Davis, California 95616, USA
| | - Leah Krubitzer
- Department of Psychology & Center for Neuroscience, University of California Davis, Davis, California 95616, USA
| | - Vivek J. Srinivasan
- Biomedical Engineering Department, University of California Davis, Davis, California 95616, USA
- Corresponding author:
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23
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Merkle CW, Srinivasan VJ. Laminar microvascular transit time distribution in the mouse somatosensory cortex revealed by Dynamic Contrast Optical Coherence Tomography. Neuroimage 2015; 125:350-362. [PMID: 26477654 DOI: 10.1016/j.neuroimage.2015.10.017] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2015] [Revised: 09/15/2015] [Accepted: 10/07/2015] [Indexed: 11/15/2022] Open
Abstract
The transit time distribution of blood through the cerebral microvasculature both constrains oxygen delivery and governs the kinetics of neuroimaging signals such as blood-oxygen-level-dependent functional Magnetic Resonance Imaging (BOLD fMRI). However, in spite of its importance, capillary transit time distribution has been challenging to quantify comprehensively and efficiently at the microscopic level. Here, we introduce a method, called Dynamic Contrast Optical Coherence Tomography (DyC-OCT), based on dynamic cross-sectional OCT imaging of an intravascular tracer as it passes through the field-of-view. Quantitative transit time metrics are derived from temporal analysis of the dynamic scattering signal, closely related to tracer concentration. Since DyC-OCT does not require calibration of the optical focus, quantitative accuracy is achieved even deep in highly scattering brain tissue where the focal spot degrades. After direct validation of DyC-OCT against dilution curves measured using a fluorescent plasma label in surface pial vessels, we used DyC-OCT to investigate the transit time distribution in microvasculature across the entire depth of the mouse somatosensory cortex. Laminar trends were identified, with earlier transit times and less heterogeneity in the middle cortical layers. The early transit times in the middle cortical layers may explain, at least in part, the early BOLD fMRI onset times observed in these layers. The layer-dependencies in heterogeneity may help explain how a single vascular supply manages to deliver oxygen to individual cortical layers with diverse metabolic needs.
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Affiliation(s)
- Conrad W Merkle
- Department of Biomedical Engineering, University of California at Davis 451 E. Health Sciences Dr. GBSF 2303 Davis CA 95616, USA
| | - Vivek J Srinivasan
- Department of Biomedical Engineering, University of California at Davis 451 E. Health Sciences Dr. GBSF 2303 Davis CA 95616, USA.
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24
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Chong SP, Merkle CW, Leahy C, Srinivasan VJ. Cerebral metabolic rate of oxygen (CMRO2) assessed by combined Doppler and spectroscopic OCT. Biomed Opt Express 2015; 6:3941-51. [PMID: 26504644 PMCID: PMC4605053 DOI: 10.1364/boe.6.003941] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Revised: 08/28/2015] [Accepted: 09/08/2015] [Indexed: 05/18/2023]
Abstract
A method of measuring cortical oxygen metabolism in the mouse brain that uses independent quantitative measurements of three key parameters: cerebral blood flow (CBF), arteriovenous oxygen extraction (OE), and hemoglobin concentration ([HbT]) is presented. Measurements were performed using a single visible light spectral/Fourier domain OCT microscope, with Doppler and spectroscopic capabilities, through a thinned-skull cranial window in the mouse brain. Baseline metabolic measurements in mice are shown to be consistent with literature values. Oxygen consumption, as measured by this method, did not change substantially during minor changes either in the fraction of inspired oxygen (FiO2) or in the fraction of inspired carbon dioxide (FiCO2), in spite of larger variations in oxygen saturations. This set of experiments supports, but does not prove, the validity of the proposed method of measuring brain oxygen metabolism.
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Affiliation(s)
- Shau Poh Chong
- Biomedical Engineering Department, University of California Davis, Davis, CA 95616, USA
| | - Conrad W Merkle
- Biomedical Engineering Department, University of California Davis, Davis, CA 95616, USA
| | - Conor Leahy
- Biomedical Engineering Department, University of California Davis, Davis, CA 95616, USA
| | - Vivek J Srinivasan
- Biomedical Engineering Department, University of California Davis, Davis, CA 95616, USA
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25
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Chong SP, Merkle CW, Leahy C, Radhakrishnan H, Srinivasan VJ. Quantitative microvascular hemoglobin mapping using visible light spectroscopic Optical Coherence Tomography. Biomed Opt Express 2015; 6:1429-50. [PMID: 25909026 PMCID: PMC4399681 DOI: 10.1364/boe.6.001429] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Revised: 02/19/2015] [Accepted: 03/14/2015] [Indexed: 05/18/2023]
Abstract
Quantification of chromophore concentrations in reflectance mode remains a major challenge for biomedical optics. Spectroscopic Optical Coherence Tomography (SOCT) provides depth-resolved spectroscopic information necessary for quantitative analysis of chromophores, like hemoglobin, but conventional SOCT analysis methods are applicable only to well-defined specular reflections, which may be absent in highly scattering biological tissue. Here, by fitting of the dynamic scattering signal spectrum in the OCT angiogram using a forward model of light propagation, we quantitatively determine hemoglobin concentrations directly. Importantly, this methodology enables mapping of both oxygen saturation and total hemoglobin concentration, or alternatively, oxyhemoglobin and deoxyhemoglobin concentration, simultaneously. Quantification was verified by ex vivo blood measurements at various pO2 and hematocrit levels. Imaging results from the rodent brain and retina are presented. Confounds including noise and scattering, as well as potential clinical applications, are discussed.
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