1. Articles from Manmohan Singh

    1-24 of 61 1 2 3 »
    1. Longitudinal assessment of the effect of alkali burns on corneal biomechanical properties using optical coherence elastography

      Longitudinal assessment of the effect of alkali burns on corneal biomechanical properties using optical coherence elastography

      Eye injury due to alkali burn is a severe ocular trauma that can profoundly affect corneal structure and function, including its biomechanical properties. Here, we assess the changes in the mechanical behavior of mouse corneas in response to alkali-induced injury by conducting longitudinal measurements using optical coherence elastography (OCE). A non-contact air-coupled ultrasound transducer was used to induce elastic waves in control and alkali-injured mouse corneas in vivo, which were imaged with phase-sensitive optical coherence tomography. Corneal mechanical properties were estimated using a modified Rayleigh-Lamb wave model, and results show that Young's modulus of alkali burned corneas were significantly ...

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    2. Multimodal imaging system combining optical coherence tomography and Brillouin microscopy for neural tube imaging

      Multimodal imaging system combining optical coherence tomography and Brillouin microscopy for neural tube imaging

      To understand the dynamics of tissue stiffness during neural tube formation and closure in a murine model, we have developed a multimodal, coaligned imaging system combining optical coherence tomography (OCT) and Brillouin microscopy. Brillouin microscopy can map the longitudinal modulus of tissue but cannot provide structural images. Thus, it is limited for imaging dynamic processes such as neural tube formation and closure. To overcome this limitation, we have combined Brillouin microscopy and OCT in one coaligned instrument. OCT provided depth-resolved structural imaging with a micrometer-scale spatial resolution to guide stiffness mapping by Brillouin modality. 2D structural and Brillouin frequency shift ...

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    3. Assessing Porcine Iris Elasticity and Mechanical Anisotropy with Optical Coherence Elastography

      Assessing Porcine Iris Elasticity and Mechanical Anisotropy with Optical Coherence Elastography

      The relaxation and contraction of the sphincter and dilator muscles of the iris play a critical role in vision, yet little is known about the biomechanic al properties of these mus cles. This study aimed to determine the elastic properties of the iris as a function of its anatomy and intraocular pressure. A high - resolution phase - sensitive OCE system was employed to detect acoustic radiation force induced propagation of elastic waves in the porcine iris in situ. Experiments were conducted at four different intraocular pressures (5, 10, 20, and 30 mmHg) with mechanical excitation at 1 kHz. We found that ...

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    4. Ultra-fast dynamic line-field optical coherence elastography

      Ultra-fast dynamic line-field optical coherence elastography

      Abstract In this work, we present an ultra-fast line-field optical coherence elastography system (LF-OCE) with an 11.5 MHz equivalent A-line rate. The system was composed of a line-field spectral domain optical coherence tomography system based on a supercontinuum light source, Michelson-type interferometer, and a high-speed 2D spectrometer. The system performed ultra-fast imaging of elastic waves in tissue-mimicking phantoms of various elasticities.

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    5. Accuracy of Common Motion Estimators in Wave-Based Optical Coherence Elastography

      Accuracy of Common Motion Estimators in Wave-Based  Optical Coherence Elastography

      Abstract. Motion estimators are commonly used in shear wave optical coherence elastography to compute small displacements. This work focuses on comparing three motion estimators: Kasai, Loupas, and the vector method. Our results show that the vector method is superi or in low - SNR, low - amplitude situations for group velocity calculation and profile reconstruction . © 202 1 Journal of Biomedical Photonics & Engineering.

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    6. Multimodal high-resolution embryonic imaging with light sheet fluorescence microscopy and optical coherence tomography

      Multimodal high-resolution embryonic imaging with light sheet fluorescence microscopy and optical coherence tomography

      A high-resolution imaging system combining optical coherence tomography (OCT) and light sheet fluorescence microscopy (LSFM) was developed. LSFM confined the excitation to only the focal plane, removing the out of plane fluorescence. This enabled imaging a murine embryo with higher speed and specificity than traditional fluorescence microscopy. OCT gives information about the structure of the embryo from the same plane illuminated by LSFM. The co-planar OCT and LSFM instrument was capable of performing co-registered functional and structural imaging of mouse embryos simultaneously.

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    7. Neural network-based image reconstruction in swept-source optical coherence tomography using undersampled spectral data

      Neural network-based image reconstruction in swept-source optical coherence tomography using undersampled spectral data

      Optical coherence tomography (OCT) is a widely used non-invasive biomedical imaging modality that can rapidly provide volumetric images of samples. Here, we present a deep learning-based image reconstruction framework that can generate swept-source OCT (SS-OCT) images using undersampled spectral data, without any spatial aliasing artifacts. This neural network-based image reconstruction does not require any hardware changes to the optical setup and can be easily integrated with existing swept-source or spectral-domain OCT systems to reduce the amount of raw spectral data to be acquired. To show the efficacy of this framework, we trained and blindly tested a deep neural network using ...

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    8. Neural network-based image reconstruction in swept-source optical coherence tomography using undersampled spectral data

      Neural network-based image reconstruction in swept-source optical coherence tomography using undersampled spectral data

      Optical Coherence Tomography (OCT) is a widely used non-invasive biomedical imaging modality that can rapidly provide volumetric images of samples. Here, we present a deep learning-based image reconstruction framework that can generate swept-source OCT (SS-OCT) images using undersampled spectral data, without any spatial aliasing artifacts. This neural network-based image reconstruction does not require any hardware changes to the optical set- up and can be easily integrated with existing swept-source or spectral domain OCT systems to reduce the amount of raw spectral data to be acquired. To show the efficacy of this framework, we trained and blindly tested a deep neural ...

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    9. Heartbeat optical coherence elastography: corneal biomechanics in vivo

      Heartbeat optical coherence elastography: corneal biomechanics in vivo

      Significance: Mechanical assessment of the cornea can provide important structural and functional information regarding its health. Current clinically available tools are limited in their efficacy at measuring corneal mechanical properties. Elastography allows for the direct estimation of mechanical properties of tissues in vivo but is generally performed using external excitation force. Aim: To show that heartbeat optical coherence elastography (Hb-OCE) can be used to assess the mechanical properties of the cornea in vivo. Approach: Hb-OCE was utilized to detect Hb-induced deformations in the rabbit cornea in vivo without the need for external excitation. Furthermore, we demonstrate how this technique can ...

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    10. Confocal air-coupled ultrasonic optical coherence elastography probe for quantitative biomechanics

      Confocal air-coupled ultrasonic optical coherence elastography probe for quantitative biomechanics

      We present an air-coupled ultrasonic radiation force probe co-focused with a phase-sensitive optical coherence tomography (OCT) system for quantitative wave-based elastography. A custom-made 1 MHz spherically focused piezoelectric transducer with a concentric 10 mm wide circular opening allowed for confocal micro-excitation of waves and phase-sensitive OCT imaging.

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    11. Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus

      Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus

      Purpose : Currently, the biomechanical properties of the corneo-scleral limbus when the eye-globe deforms are largely unknown. The purpose of this study is to evaluate changes in elasticity of the cornea, sclera, and limbus when subjected to different intraocular pressures (IOP) using wave-based optical coherence elastography (OCE). Special attention was given to the elasticity changes of the limbal region with respect to the elasticity variations in the neighboring corneal and scleral regions. Methods : Continuous harmonic elastic waves (800 Hz) were mechanically induced in the sclera near the corneo-sclera limbus of in situ porcine eye-globes ( n = 8). Wave propagation was imaged using ...

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    12. Optical coherence tomography angiography to evaluate murine fetal brain vasculature changes caused by prenatal exposure to nicotine

      Optical coherence tomography angiography to evaluate murine fetal brain vasculature changes caused by prenatal exposure to nicotine

      Maternal smoking causes several defects ranging from intrauterine growth restriction to sudden infant death syndrome and spontaneous abortion. While several studies have documented the effects of prenatal nicotine exposure in development and behavior, acute vasculature changes in the fetal brain due to prenatal nicotine exposure have not been evaluated yet. This study uses correlation mapping optical coherence angiography to evaluate changes in fetal brain vasculature flow caused by maternal exposure to nicotine during the second trimester-equivalent of gestation in a mouse model. The effects of two different doses of nicotine were evaluated. Results showed a decrease in the vasculature for ...

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    13. Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography

      Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography

      Significance: It is generally agreed that the corneal mechanical properties are strongly linked to many eye diseases and could be used to assess disease progression and response to therapies. Elastography is the most notable method of assessing corneal mechanical properties, but it generally requires some type of external excitation to induce a measurable displacement in the tissue. Aim: We present Heartbeat Optical Coherence Elastography (Hb-OCE), a truly passive method that can measure the elasticity of the cornea based on intrinsic corneal displacements induced by the heartbeat. Approach: Hb-OCE measurements were performed in untreated and UV-A/riboflavin cross-linked porcine corneas ex ...

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    14. Multimodal quantitative optical elastography of the crystalline lens with optical coherence elastography and Brillouin microscopy

      Multimodal quantitative optical elastography of the crystalline lens with optical coherence elastography and Brillouin microscopy

      Assessing the biomechanical properties of the crystalline lens can provide crucial information for diagnosing disease and guiding precision therapeutic interventions. Existing noninvasive methods have been limited to global measurements. Here, we demonstrate the quantitative assessment of the elasticity of crystalline lens with a multimodal optical elastography technique, which combines dynamic wave-based optical coherence elastography (OCE) and Brillouin microscopy to overcome the drawbacks of individual modalities. OCE can provide direct measurements of tissue elasticity rapidly and quantitatively, but it is a challenge to image transparent samples such as the lens because this technique relies on backscattered light. On the other hand ...

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    15. Assessing the Acute Effects of Prenatal Synthetic Cannabinoid Exposure on Murine Fetal Brain Vasculature Using Optical Coherence Tomography

      Assessing the Acute Effects of Prenatal Synthetic Cannabinoid Exposure on Murine Fetal Brain Vasculature Using Optical Coherence Tomography

      Marijuana is one of the most commonly abused substances during pregnancy. Synthetic cannabinoids (SCBs) are a group of heterogeneous compounds that are 40‐ to 600‐fold more potent than ∆ 9 ‐tetrahydrocannabinol , the major psychoactive component of marijuana. With SCBs being legally available for purchase and the prevalence of unplanned pregnancies, the possibility of prenatal exposure to SCBs is high. However, the effects of prenatal SCB exposure on embryonic brain development are not well understood. In this study, we use complex correlation mapping optical coherence angiography to evaluate changes in murine fetal brain vasculature in utero , minutes after maternal exposure to ...

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    16. Optical coherence elastography of cold cataract in porcine lens

      Optical coherence elastography of cold cataract in porcine lens

      Cataract is one of the most prevalent causes of blindness around the world. Understanding the mechanisms of cataract development and progression is important for clinical diagnosis and treatment. Cold cataract has proven to be a robust model for cataract formation that can be easily controlled in the laboratory. There is evidence that the biomechanical properties of the lens can be significantly changed by cataract. Therefore, early detection of cataract, as well as evaluation of therapies, could be guided by characterization of lenticular biomechanical properties. In this work, we utilized optical coherence elastography (OCE) to monitor the changes in biomechanical properties ...

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    17. Assessing the biomechanical properties of the porcine crystalline lens as a function of intraocular pressure with optical coherence elastography

      Assessing the biomechanical properties of the porcine crystalline lens as a function of intraocular pressure with optical coherence elastography

      In this study, we investigated the relationship between the biomechanical properties of the crystalline lens and intraocular pressure (IOP) using a confocal acoustic radiation force (ARF) and phase-sensitive optical coherence elastography (OCE) system. ARF induced a small displacement at the apex of porcine lenses in situ at various artificially controlled IOPs. Maximum displacement, relaxation rate, and Young’s modulus were utilized to assess the stiffness of the crystalline lens. The results showed that the stiffness of the crystalline increased as IOP increased, but the lens stiffening was not as significant as the stiffening of other ocular tissues such as the ...

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    18. Modified wavelength scanning interferometry for simultaneous tomography and topography of the cornea with Fourier domain optical coherence tomography

      Modified wavelength scanning interferometry for simultaneous tomography and topography of the cornea with Fourier domain optical coherence tomography

      Visual acuity is dependent on corneal shape and size. A minor variation in surface geometry can cause a deformation of corneal geometry, which affects its optical performance. In this work we demonstrate an algorithm for the simultaneous measurement of corneal tomography and topography with a traditional point-scanning Fourier domain optical coherence tomography (FD-OCT) system. A modified wavelength scanning interferometry (mWSI) algorithm enabled topographical evaluation of the surface with nanometer-scale resolution, which is superior to the micrometer-scale resolution of traditional OCT structural imaging. We validated the technique with an optically flat mirror, standard roughness gauges, and atomic force microscopy (AFM). The ...

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    19. Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography

      Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography

      Purpose To quantify the effects of the hydration state on the Young's modulus of the cornea . Setting Biomedical Optics Laboratory, University of Houston, Houston, Texas, USA. Design Experimental study. Methods Noncontact, dynamic optical coherence elastography (OCE) measurements were taken of in situ rabbit corneas in the whole eye–globe configuration (n = 10) and at an artificially controlled intraocular pressure of 15 mm Hg. Baseline OCE measurements were taken by topically hydrating the corneas with saline for 1 hour. The corneas were then dehydrated topically with a 20% dextran solution for another hour, and the OCE measurements were repeated. A ...

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    20. Effects of Thickness on Corneal Biomechanical Properties Using Optical Coherence Elastography

      Effects of Thickness on Corneal Biomechanical Properties Using Optical Coherence Elastography

      SIGNIFICANCE Measured corneal biomechanical properties are driven by intraocular pressure, tissue thickness, and inherent material properties. We demonstrate tissue thickness as an important factor in the measurement of corneal biomechanics that can confound short-term effects due to UV riboflavin cross-linking (CXL) treatment. PURPOSE We isolate the effects of tissue thickness on the measured corneal biomechanical properties using optical coherence elastography by experimentally altering the tissue hydration state and stiffness. METHODS Dynamic optical coherence elastography was performed using phase-sensitive optical coherence tomography imaging to quantify the tissue deformation dynamics resulting from a spatially discrete, low-force air pulse (150-μm spot size ...

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    21. Quantifying changes in lens biomechanical properties due to cold cataract with optical coherence elastography

      Quantifying changes in lens biomechanical properties due to cold cataract with optical coherence elastography

      Cataract is the most prevalent cause of visual impairment worldwide. Cataracts can be formed due to trauma, radiation, drug abuse, or low temperatures. Thus, early detection of cataract can be immensely helpful for preserving visual acuity by ensuring that the appropriate therapeutic procedures are performed at earlier stages of disease onset and progression. In this work, we utilized a phase-sensitive optical coherence elastography (OCE) system to quantify changes in biomechanical properties of porcine lenses in vitro with induced cold cataracts. The results show significant increase in lens Young’s modulus due to formation of the cold cataract (from ~ 35 kPa ...

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    22. Biomechanical assessment of myocardial infarction using optical coherence elastography

      Biomechanical assessment of myocardial infarction using optical coherence elastography

      Myocardial infarction (MI) leads to cardiomyocyte loss, impaired cardiac function, and heart failure. Molecular genetic analyses of myocardium in mouse models of ischemic heart disease have provided great insight into the mechanisms of heart regeneration, which is promising for novel therapies after MI. Although biomechanical factors are considered an important aspect in cardiomyocyte proliferation, there are limited methods for mechanical assessment of the heart in the mouse MI model. This prevents further understanding the role of tissue biomechanics in cardiac regeneration. Here we report optical coherence elastography (OCE) of the mouse heart after MI. Surgical ligation of the left anterior ...

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    23. Common-path phase-sensitive optical coherence tomography provides enhanced phase stability and detection sensitivity for dynamic elastography

      Common-path phase-sensitive optical coherence tomography provides enhanced phase stability and detection sensitivity for dynamic elastography

      Phase-sensitive optical coherence elastography (PhS-OCE) is an emerging optical technique to quantify soft-tissue biomechanical properties. We implemented a common-path OCT design to enhance displacement sensitivity and optical phase stability for dynamic elastography imaging. The background phase stability was greater in common-path PhS-OCE (0.24 ± 0.07nm) than conventional PhS-OCE (1.60 ± 0.11μm). The coefficient of variation for surface displacement measurements using conventional PhS-OCE averaged 11% versus 2% for common-path PhS-OCE. Young’s modulus estimates showed good precision (95% CIs) for tissue phantoms: 24.96 ± 2.18kPa (1% agar), 49.69 ± 4.87kPa (1.5% agar), and 116.08 ...

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    24. Comparison and combination of rotational imaging optical coherence tomography and selective plane illumination microscopy for embryonic study

      Comparison and combination of rotational imaging optical coherence tomography and selective plane illumination microscopy for embryonic study

      Several optical imaging techniques have been applied for high-resolution embryonic imaging using different contrast mechanisms, each with their own benefits and limitations. In this study, we imaged the same E9.5 mouse embryo with rotational imaging optical coherence tomography (RI-OCT) and selective plane illumination microscopy (SPIM). RI-OCT overcomes optical penetration limits of traditional OCT imaging that prohibit full-body imaging of mouse embryos at later stages by imaging the samples from multiple angles. SPIM enables high-resolution, 3D imaging with less phototoxicity and photobleaching than laser scanning confocal microscopy (LSCM) by illuminating the sample with a focused sheet of light. Side by ...

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    1-24 of 61 1 2 3 »
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