1. Articles from Sava Sakadžic

    1-16 of 16
    1. Measurement of shear-induced diffusion of red blood cells using dynamic light scattering-optical coherence tomography

      Measurement of shear-induced diffusion of red blood cells using dynamic light scattering-optical coherence tomography

      Dynamic Light Scattering-Optical Coherence Tomography (DLS-OCT) takes the advantages of using DLS to measure particle flow and diffusion within an OCT resolution-constrained 3D volume, enabling the simultaneous measurements of absolute RBC velocity and diffusion coefficient with high spatial resolution. In this work, we applied DLS-OCT to measure both RBC velocity and the shear-induced diffusion coefficient within penetrating venules of the somatosensory cortex of anesthetized mice. Blood flow laminar profile measurements indicate a blunted laminar flow profile, and the degree of blunting decreases with increasing vessel diameter. The measured shear-induced diffusion coefficient was proportional to the flow shear rate with a ...

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    2. Characterizing the optical properties of human brain tissue with high numerical aperture optical coherence tomography

      Characterizing the optical properties of human brain tissue with high numerical aperture optical coherence tomography

      Quantification of tissue optical properties with optical coherence tomography (OCT) has proven to be useful in evaluating structural characteristics and pathological changes. Previous studies primarily used an exponential model to analyze low numerical aperture (NA) OCT measurements and obtain the total attenuation coefficient for biological tissue. In this study, we develop a systematic method that includes the confocal parameter for modeling the depth profiles of high NA OCT, when the confocal parameter cannot be ignored. This approach enables us to quantify tissue optical properties with higher lateral resolution. The model parameter predictions for the scattering coefficients were tested with calibrated ...

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    3. Shear-Induced Diffusion of Red Blood Cells Measured with Dynamic Light Scattering-Optical Coherence Tomography

      Shear-Induced Diffusion of Red Blood Cells Measured with Dynamic Light Scattering-Optical Coherence Tomography

      Quantitative measurements of intravascular microscopic dynamics, such as absolute blood flow velocity, shear stress, and the diffusion coefficient of red blood cells (RBCs), are fundamental to understanding the blood flow behavior within the microcirculation, and for understanding why diffuse correlation spectroscopy (DCS) measurements of blood flow are dominantly sensitive to the diffusive motion of RBCs. Dynamic Light Scattering-Optical Coherence Tomography (DLS-OCT) takes the advantages of using DLS to measure particle flow and diffusion within an OCT resolution-constrained 3D volume, enabling the simultaneous measurements of absolute RBC velocity and diffusion coefficient with high spatial resolution. In this work, we applied DLS-OCT ...

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    4. Impact of temporal resolution on estimating capillary RBC-flux with optical coherence tomography

      Impact of temporal resolution on estimating capillary RBC-flux with optical coherence tomography

       Optical coherence tomography (OCT) has been used to measure capillary red blood cell (RBC) flux. However, one important technical issue is that the accuracy of this method is subject to the temporal resolution (ΔtΔt) of the repeated RBC-passage B-scans. A ceiling effect arises due to an insufficient ΔtΔt limiting the maximum RBC-flux that can be measured. In this letter, we first present simulations demonstrating that Δt=1.5  msΔt=1.5  mspermits measuring RBC-flux up to 150  RBCs/s150  RBCs/s with an underestimation of 9%. The simulations further show that measurements with Δt=3 ...

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    5. Microstructural characterization of myocardial infarction with optical coherence tractography and two‐photon microscopy

      Microstructural characterization of myocardial infarction with optical coherence tractography and two‐photon microscopy

      Myocardial infarction leads to complex changes in the fiber architecture of the heart. Here, we present a novel optical approach to characterize these changes in intact hearts in three dimensions. Optical coherence tomography (OCT) was used to derive a depth‐resolved field of orientation on which tractography was performed. Tractography of healthy myocardium revealed a smooth linear transition in fiber inclination or helix angle from the epicardium to endocardium. Conversely, in infarcted hearts, no coherent microstructure could be identified in the infarct with OCT. Additional characterization of the infarct was performed by the measurement of light attenuation and with two ...

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    6. Polarization sensitive optical coherence microscopy for brain imaging

      Polarization sensitive optical coherence microscopy for brain imaging

      Optical coherence tomography (OCT) and optical coherence microscopy (OCM) have demonstrated the ability to investigate cyto- and myelo-architecture in the brain. Polarization-sensitive OCT provides sensitivity to additional contrast mechanisms, specifically the birefringence of myelination and, therefore, is advantageous for investigating white matter fiber tracts. In this Letter, we developed a polarization-sensitive optical coherence microscope (PS-OCM) with a 3.5 μm axial and 1.3 μm transverse resolution to investigate fiber organization and orientation at a finer scale than previously demonstrated with PS-OCT. In a reconstructed mouse brain section, we showed that at the focal depths of 20–70 μm, the ...

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    7. Multimodal reconstruction of microvascular-flow distributions using combined two-photon microscopy and Doppler optical coherence tomography

      Multimodal reconstruction of microvascular-flow distributions using combined two-photon microscopy and Doppler optical coherence tomography

      Computing microvascular cerebral blood flow ( μ CBF ) in real cortical angiograms is challenging. Here, we investigated whether the use of Doppler optical coherence tomography (DOCT) flow measurements in individual vessel segments can help in reconstructing μ CBF across the entire vasculature of a truncated cortical angiogram. A μ CBF computational framework integrating DOCT measurements is presented. Simulations performed on a synthetic angiogram showed that the addition of DOCT measurements, especially close to large inflowing or outflowing vessels, reduces the impact of pressure boundary conditions and estimated vessel resistances resulting in a more accurate reconstruction of μ CBF . Our technique was then applied to reconstruct ...

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    8. Optical coherence tomography visualizes neurons in human entorhinal cortex

      Optical coherence tomography visualizes neurons in human entorhinal cortex

      The cytoarchitecture of the human brain is of great interest in diverse fields: neuroanatomy, neurology, neuroscience, and neuropathology. Traditional histology is a method that has been historically used to assess cell and fiber content in the ex vivo human brain. However, this technique suffers from significant distortions. We used a previously demonstrated optical coherence microscopy technique to image individual neurons in several square millimeters of en-face tissue blocks from layer II of the human entorhinal cortex, over 50     μ m in depth. The same slices were then sectioned and stained for Nissl substance. We registered the optical coherence tomography (OCT) images ...

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    9. Feature Of The Week 10/20/13: Multiparametric, Longitudinal Optical Coherence Tomography Imaging Reveals Acute Injury and Chronic Recovery in Experimental Ischemic Stroke

      Feature Of The Week 10/20/13: Multiparametric, Longitudinal Optical Coherence Tomography Imaging Reveals Acute Injury and Chronic Recovery in Experimental Ischemic Stroke

      To better understand pathophysiology during brain injuries such as stroke, we combined a number of OCT imaging techniques. Namely, we employed Doppler methods to map blood flow, angiography methods to measure capillary-level perfusion and vessel diameter, and scattering quantification methods to determine cell viability. This multi-parametric approach was used to perform imaging in the acute and recovery stages in experimental ischemic stroke, with the goal of determining the fate of the penumbra using imaging biomarkers. The penumbra is an area of brain tissue which is compromised during stroke but could be salvaged through thrombolysis or other treatment methods. Multi-parametric imaging ...

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    10. Multiparametric, Longitudinal Optical Coherence Tomography Imaging Reveals Acute Injury and Chronic Recovery in Experimental Ischemic Stroke

      Multiparametric, Longitudinal Optical Coherence Tomography Imaging Reveals Acute Injury and Chronic Recovery in Experimental Ischemic Stroke

      Progress in experimental stroke and translational medicine could be accelerated by high-resolution in vivo imaging of disease progression in the mouse cortex. Here, we introduce optical microscopic methods that monitor brain injury progression using intrinsic optical scattering properties of cortical tissue. A multi-parametric Optical Coherence Tomography (OCT) platform for longitudinal imaging of ischemic stroke in mice, through thinned-skull, reinforced cranial window surgical preparations, is described. In the acute stages, the spatiotemporal interplay between hemodynamics and cell viability, a key determinant of pathogenesis, was imaged. In acute stroke, microscopic biomarkers for eventual infarction, including capillary non-perfusion, cerebral blood flow deficiency, altered ...

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    11. Optical coherence tractography using intrinsic contrast

      Optical coherence tractography using intrinsic contrast

      Organs such as the heart and brain possess intricate fiber structures that are best characterized with three-dimensional imaging. For instance, diffusion-based, magnetic resonance tractography (MRT) enables studies of connectivity and remodeling during development and disease macroscopically on the millimeter scale. Here we present complementary, high-resolution microscopic optical coherence imaging and analysis methods that, when used in conjunction with clearing techniques, can characterize fiber architecture in intact organs at tissue depths exceeding 1 mm. We anticipate that these techniques can be used to study fiber architecture in situ at microscopic scales not currently accessible to diffusion magentic resonance (MR), and thus ...

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    12. Frontiers in optical imaging of cerebral blood flow and metabolism

      Frontiers in optical imaging of cerebral blood flow and metabolism

      In vivo optical imaging of cerebral blood flow (CBF) and metabolism did not exist 50 years ago. While point optical fluorescence and absorption measurements of cellular metabolism and hemoglobin concentrations had already been introduced by then, point blood flow measurements appeared only 40 years ago. The advent of digital cameras has significantly advanced two-dimensional optical imaging of neuronal, metabolic, vascular, and hemodynamic signals. More recently, advanced laser sources have enabled a variety of novel three-dimensional high-spatial-resolution imaging approaches. Combined, as we discuss here, these methods are permitting a multifaceted investigation of the local regulation of CBF and metabolism with unprecedented ...

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    13. Microvascular oxygen tension and flow measurements in rodent cerebral cortex during baseline conditions and functional activation

      Microvascular oxygen tension and flow measurements in rodent cerebral cortex during baseline conditions and functional activation

      Measuring cerebral oxygen delivery and metabolism microscopically is important for interpreting macroscopic functional magnetic resonance imaging (fMRI) data and identifying pathological changes associated with stroke, Alzheimer's disease, and brain injury. Here, we present simultaneous, microscopic measurements of cerebral blood flow (CBF) and oxygen partial pressure (pO(2)) in cortical microvessels of anesthetized rats under baseline conditions and during somatosensory stimulation. Using a custom-built imaging system, we measured CBF with Fourier-domain optical coherence tomography (OCT), and vascular pO(2) with confocal phosphorescence lifetime microscopy. Cerebral blood flow and pO(2) measurements displayed heterogeneity over distances irresolvable with fMRI and positron ...

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    14. Optically based quantification of absolute cerebral metabolic rate of oxygen (CMRO2) with high spatial resolution in rodents

      Optically based quantification of absolute cerebral metabolic rate of oxygen (CMRO2) with high spatial resolution in rodents

      Measuring oxygen delivery in brain tissue is important for identifying the pathophysiological changes associated with brain injury and various diseases such as cancer, stroke, and Alzheimer's disease. We have developed a multi-modal imaging system for minimally invasive measurement of cerebral oxygenation and blood flow in small animals with high spatial resolution. The system allows for simultaneous measurement of blood flow using Fourier-domain optical coherence tomography, and oxygen partial pressure (pO2) using either confocal or multiphoton phosphorescence lifetime imaging with exogenous porphyrin-based dyes sensitive to dissolved oxygen. Here we present the changes in pO2 and blood flow in superficial cortical ...

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    15. Quantitative cerebral blood flow with Optical Coherence Tomography

      Quantitative cerebral blood flow with Optical Coherence Tomography

      Vivek J. Srinivasan, Sava Sakadžić, Iwona Gorczynska, Svetlana Ruvinskaya, Weicheng Wu, James G. Fujimoto, David A. BoasAbsolute measurements of cerebral blood flow (CBF) are an important endpoint in studies of cerebral pathophysiology. Currently no accepted method exists for in vivo longitudinal monitoring of CBF with high resolution in rats and mice. Using three-dimensional Doppler Optical Coherence Tomography and ... [Opt. Express 18, 2477-2494 (2010)]

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    16. Depth-resolved microscopy of cortical hemodynamics with optical coherence tomography

      Depth-resolved microscopy of cortical hemodynamics with optical coherence tomography

      We describe depth-resolved microscopy of cortical hemodynamics with high-speed spectral/Fourier domain optical coherence tomography (OCT). Stimulus-evoked changes in blood vessel diameter, flow, and total hemoglobin were measured in the rat somatosensory cortex. The results show OCT measurements of hemodynamic changes during functional activation and represent an important step toward understanding functional hyperemia at the microscopic level.

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    1-16 of 16
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  2. Topics in the News

    1. (13 articles) Harvard University
    2. (12 articles) Massachusetts General Hospital
    3. (12 articles) David A. Boas
    4. (9 articles) Vivek J. Srinivasan
    5. (5 articles) Massachusetts Institute of Technology
    6. (4 articles) Harsha Radhakrishnan
    7. (3 articles) UC Davis
    8. (3 articles) James G. Fujimoto
    9. (3 articles) Iwona Gorczynska
    10. (3 articles) Hui Wang
    11. (2 articles) The Chinese University of Hong Kong
    12. (1 articles) National University of Singapore
    13. (1 articles) University of Groningen
    14. (1 articles) Shanghai Jiao Tong University
    15. (1 articles) University of Catania
    16. (1 articles) Singapore Eye Research Institute
    17. (1 articles) Erasmus University
    18. (1 articles) Tien Yin Wong
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    Depth-resolved microscopy of cortical hemodynamics with optical coherence tomography Quantitative cerebral blood flow with Optical Coherence Tomography Optically based quantification of absolute cerebral metabolic rate of oxygen (CMRO2) with high spatial resolution in rodents Microvascular oxygen tension and flow measurements in rodent cerebral cortex during baseline conditions and functional activation Frontiers in optical imaging of cerebral blood flow and metabolism Optical coherence tractography using intrinsic contrast Multiparametric, Longitudinal Optical Coherence Tomography Imaging Reveals Acute Injury and Chronic Recovery in Experimental Ischemic Stroke Feature Of The Week 10/20/13: Multiparametric, Longitudinal Optical Coherence Tomography Imaging Reveals Acute Injury and Chronic Recovery in Experimental Ischemic Stroke Polarization sensitive optical coherence microscopy for brain imaging Microstructural characterization of myocardial infarction with optical coherence tractography and two‐photon microscopy Thorlabs Releases New MEMS‐VCSEL Swept‐Wavelength Laser Sources Upcoming imaging concepts and their impact on treatment planning and treatment response in radiation oncology