1. Articles from David A. Boas

    1-24 of 42 1 2 »
    1. Measuring Capillary Flow Dynamics using Interlaced Two-Photon Volumetric Scanning

      Measuring Capillary Flow Dynamics using Interlaced Two-Photon Volumetric Scanning

      Two photon microscopy and optical coherence tomography (OCT) are two standard methods for measuring flow speeds of red blood cells in microvessels, particularly in animal models. However, traditional two photon microscopy lacks the depth of field to adequately capture the full volumetric complexity of the cerebral microvasculature and OCT lacks the specificity offered by fluorescent labeling. In addition, the traditional raster scanning technique utilized in both modalities requires a balance of image frame rate and field of view, which severely limits the study of RBC velocities in the microvascular network. Here, we overcome this by using a custom two photon ...

      Read Full Article
    2. A novel algorithm for multiplicative speckle noise reduction in ex vivo human brain OCT images

      A novel algorithm for multiplicative speckle noise reduction in ex vivo human brain OCT images

      Optical coherence tomography (OCT) images of ex vivo human brain tissue are corrupted by multiplicative speckle noise that degrades the contrast to noise ratio (CNR) of microstructural compartments. This work proposes a novel algorithm to reduce noise corruption in OCT images that minimizes the penalized negative log likelihood of gamma distributed speckle noise. The proposed method is formulated as a majorize-minimize problem that reduces to solving an iterative regularized least squares optimization. We demonstrate the usefulness of the proposed method by removing speckle in simulated data, phantom data and real OCT images of human brain tissue. We compare the proposed ...

      Read Full Article
    3. Refractive-index matching enhanced polarization sensitive optical coherence tomography quantification in human brain tissue

      Refractive-index matching enhanced polarization sensitive optical coherence tomography quantification in human brain tissue

      The importance of polarization-sensitive optical coherence tomography (PS-OCT) has been increasingly recognized in human brain imaging. Despite the recent progress of PS-OCT in revealing white matter architecture and orientation, quantification of fine-scale fiber tracts in the human brain cortex has been a challenging problem, due to a low birefringence in the gray matter. In this study, we investigated the effect of refractive index matching by 2,2’-thiodiethanol (TDE) immersion on the improvement of PS-OCT measurements in ex vivo human brain tissue. We show that we can obtain fiber orientation maps of U-fibers that underlie sulci, as well as cortical ...

      Read Full Article
    4. Scalable mapping of myelin and neuron density in the human brain with micrometer resolution

      Scalable mapping of myelin and neuron density in the human brain with micrometer resolution

      Optical coherence tomography (OCT) is an emerging 3D imaging technique that allows quantification of intrinsic optical properties such as scattering coefficient and back-scattering coefficient, and has proved useful in distinguishing delicate microstructures in the human brain. The origins of scattering in brain tissues are contributed by the myelin content, neuron size and density primarily; however, no quantitative relationships between them have been reported, which hampers the use of OCT in fundamental studies of architectonic areas in the human brain and the pathological evaluations of diseases. Here, we built a generalized linear model based on Mie scattering theory that quantitatively links ...

      Read Full Article
    5. Refractive-index matching enhanced polarization-sensitive optical coherence tomography quantification in human brain tissue

      Refractive-index matching enhanced polarization-sensitive optical coherence tomography quantification in human brain tissue

      The importance of polarization-sensitive optical coherence tomography (PS-OCT) has been increasingly recognized in human brain imaging. Despite the recent progress of PS-OCT in revealing white matter architecture and orientation, quantification of fine-scale fiber tracts in the human brain cortex has been a challenging problem, due to a low birefringence in the gray matter. In this study, we investigated the effect of refractive index matching by 2,2'-thiodiethanol (TDE) immersion on the improvement of PS-OCT measurements in ex vivo human brain tissue. We obtain the cortical fiber orientation maps in the gray matter, which reveals the radial fibers in the ...

      Read Full Article
    6. Scalable mapping of myelin and neuron density in the human brain with micrometer resolution

      Scalable mapping of myelin and neuron density in the human brain with micrometer resolution

      Optical Coherence Tomography (OCT) is an emerging 3D imaging technique that allows quantification of intrinsic optical properties such as scattering coefficient and back-scattering coefficient, and has proved useful in distinguishing delicate microstructures in the human brain. The origins of scattering in brain tissues are contributed by the myelin content, neuron size and density primarily; however, no quantitative relationships between them have been reported, which hampers the use of OCT in fundamental studies of architectonic areas in the human brain and the pathological evaluations of diseases. To date, histology remains the golden standard, which is prone to errors and can only ...

      Read Full Article
    7. Imaging localized fast optical signals of neural activation with optical coherence tomography in awake mice

      Imaging localized fast optical signals of neural activation with optical coherence tomography in awake mice

      We report optical coherence tomography (OCT) imaging of localized fast optical signals (FOSs) arising from whisker stimulation in awake mice. The activated voxels were identified by fitting the OCT intensity signal time course with a response function over a time scale of a few hundred milliseconds after the whisker stimulation. The significantly activated voxels were shown to be localized to the expected brain region for whisker stimulation. The ability to detect functional stimulus-evoked, depth-resolved FOS with intrinsic contrast from the cortex provides a new tool for neural activity studies.

      Read Full Article
    8. Measuring myelin content and cell density in the human brain using optical coherence tomography

      Measuring myelin content and cell density in the human brain using optical coherence tomography

      Serial Sectioning Optical Coherence Tomography(serial sectioning OCT) has been widely used to investigate the structural and pathological features of brain samples. OCT is an optical imaging technique that provides both the 3D structure of the tissue as well as the optical properties including the scattering coefficient (μ s ) and back-scattering coefficient (μ b ). Serial sectioning OCT allows the reconstruction of distortion-free volumetric images at high contrast and high resolution, which has proven to be useful for the detection of cancerous tissue boundaries, visualizing 3D vascular structures and measuring neuron density. The tissue optical properties extracted from the OCT depth profile has ...

      Read Full Article
    9. Improving the characterization of ex vivo human brain optical properties using high numerical aperture optical coherence tomography by spatially constraining the confocal parameters

      Improving the characterization of ex vivo human brain optical properties using high numerical aperture optical coherence tomography by spatially constraining the confocal parameters

      Significance: The optical properties of biological samples provide information about the structural characteristics of the tissue and any changes arising from pathological conditions. Optical coherence tomography (OCT) has proven to be capable of extracting tissue's optical properties using a model that combines the exponential decay due to tissue scattering and the axial point spread function that arises from the confocal nature of the detection system, particularly for higher numerical aperture (NA) measurements. A weakness in estimating the optical properties is the inter-parameter cross-talk between tissue scattering and the confocal parameters defined by the Rayleigh range and the focus depth ...

      Read Full Article
    10. Insight into the fundamental trade-offs of diffusion MRI from polarization-sensitive optical coherence tomography in ex vivo human brain

      Insight into the fundamental trade-offs of diffusion MRI from polarization-sensitive optical coherence tomography in ex vivo human brain

      In the first study comparing high angular resolution diffusion MRI (dMRI) in the human brain to axonal orientation measurements from polarization-sensitive optical coherence tomography (PSOCT), we compare the accuracy of orientation estimates from various dMRI sampling schemes and reconstruction methods. We find that, if the reconstruction approach is chosen carefully, single-shell dMRI data can yield the same accuracy as multi-shell data, and only moderately lower accuracy than a full Cartesian-grid sampling scheme. Our results suggest that current dMRI reconstruction approaches do not benefit substantially from ultra-high b-values or from very large numbers of diffusion-encoding directions. We also show that accuracy ...

      Read Full Article
    11. Normalized field autocorrelation function-based optical coherence tomography three-dimensional angiography

      Normalized field autocorrelation function-based optical coherence tomography three-dimensional angiography

      Optical coherence tomography angiography (OCTA) has been widely used for <i>en face</i> visualization of the microvasculature, but is challenged for real three-dimensional (3-D) topologic imaging due to the “tail” artifacts that appear below large vessels. Further, OCTA is generally incapable of differentiating descending arterioles from ascending venules. We introduce a normalized field autocorrelation function-based OCTA (<i>g</i><sub>1</sub>-OCTA), which minimizes the tail artifacts and is capable of distinguishing penetrating arterioles from venules in the 3-D image. <i>g</i><sub>1</sub>   (  τ  )   is calculated from repeated optical coherence tomography (OCT) acquisitions for each spatial ...

      Read Full Article
    12. Capillary red blood cell velocimetry by phase-resolved optical coherence tomography

      Capillary red blood cell velocimetry by phase-resolved optical coherence tomography

      Quantitative measurement of blood flow velocity in capillaries is challenging due to their small size (around 5-10 μm), and the discontinuity and single-file feature of RBCs flowing in a capillary. In this work, we present a phase-resolved Optical Coherence Tomography (OCT) method for accurate measurement of the red blood cell (RBC) speed in cerebral capillaries. To account for the discontinuity of RBCs flowing in capillaries, we applied an M-mode scanning strategy that repeated A-scans at each scanning position for an extended time. As the capillary size is comparable to the OCT resolution size (3.5×3.5×3.5μm ...

      Read Full Article
    13. 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 ...

      Read Full Article
    14. 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 ...

      Read Full Article
    15. Capillary red blood cell velocimetry by phase-resolved optical coherence tomography

      Capillary red blood cell velocimetry by phase-resolved optical coherence tomography

      We present a phase-resolved optical coherence tomography (OCT) method to extend Doppler OCT for the accurate measurement of the red blood cell (RBC) velocity in cerebral capillaries. OCT data were acquired with an M-mode scanning strategy (repeated A-scans) to account for the single-file passage of RBCs in a capillary, which were then high-pass filtered to remove the stationary component of the signal to ensure an accurate measurement of phase shift of flowing RBCs. The angular frequency of the signal from flowing RBCs was then quantified from the dynamic component of the signal and used to calculate the axial speed of ...

      Read Full Article
    16. 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 in 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 three‐dimensional volume, enabling the simultaneous measurements of absolute RBC velocity and diffusion coefficient with high spatial resolution. In this ...

      Read Full Article
    17. 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 ...

      Read Full Article
    18. Polarization-sensitive optical coherence tomography of the human brain connectome

      Polarization-sensitive optical coherence tomography of the human brain connectome

      The human brain is composed of approximately 100 billion neurons that ‘communicate’ through an intricate network of axons and dendrites. 1 The difficulty of tracing these 3D neuronal pathways, however, has been a critical barrier for standard histology (the study of microscopic anatomy) over the past 100 years. Indeed, there is still no technology that can be used to acquire microscopic images in undistorted 3D space for mapping human brain connectivity. Currently available techniques for 3D brain mapping include histological staining and polarized light imaging. 2, 3 In these approaches, 2D image slices are obtained, but these must be physically ...

      Read Full Article
    19. 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 ...

      Read Full Article
    20. Optical coherence tomography imaging of capillary reperfusion after ischemic stroke

      Optical coherence tomography imaging of capillary reperfusion after ischemic stroke

      Although progress has been made for recanalization therapies after ischemic stroke, post-treatment imaging studies show that tissue reperfusion cannot be attained despite satisfactory recanalization in a significant percentage of patients. Hence, investigation of microcirculatory changes in both surface and deep cortical levels after ischemia reperfusion is important for understanding the post-stroke blood flow dynamics. In this study, we applied optical coherence tomography (OCT) imaging of cerebral blood flow for the quantification of the microcirculatory changes. We obtained OCT microangiogram of the brain cortex in a mouse stroke model and analyzed the data to trace changes in the capillary perfusion level ...

      Read Full Article
    21. 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 ...

      Read Full Article
    22. 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 ...

      Read Full Article
    1-24 of 42 1 2 »
  1. Categories

    1. Applications:

      Art, Cardiology, Dentistry, Dermatology, Developmental Biology, Gastroenterology, Gynecology, Microscopy, NDE/NDT, Neurology, Oncology, Ophthalmology, Other Non-Medical, Otolaryngology, Pulmonology, Urology
    2. Business News:

      Acquisition, Clinical Trials, Funding, Other Business News, Partnership, Patents
    3. Technology:

      Broadband Sources, Probes, Tunable Sources
    4. Miscellaneous:

      Jobs & Studentships, Student Theses, Textbooks
  2. Topics in the News

    1. (33 articles) Massachusetts General Hospital
    2. (28 articles) Harvard University
    3. (15 articles) Boston University
    4. (13 articles) Massachusetts Institute of Technology
    5. (4 articles) Thorlabs
    6. (3 articles) Brown University
    7. (2 articles) University of Minnesota
    8. (2 articles) Polytechnique Montreal
    9. (1 articles) University of Maryland
    10. (1 articles) The Chinese University of Hong Kong
  3. Popular Articles

  4. Picture Gallery

    Depth-resolved microscopy of cortical hemodynamics with optical coherence tomography Rapid volumetric angiography of cortical microvasculature 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 Optical coherence tomography for the quantitative study of cerebrovascular physiology Motion correction for phase-resolved dynamic optical coherence tomography imaging of rodent cerebral cortex Frontiers in optical imaging of cerebral blood flow and metabolism Handbook of Biomedical Optics (Book) Quantitative imaging of cerebral blood flow velocity and intracellular motility using dynamic light scattering–optical coherence tomography Editorial – Optical Coherence Tomography Angiography: Considerations Regarding Diagnostic Parameters Imaging of the optic nerve: technological advances and future prospects Optical coherence tomography assessment of pulmonary vascular remodeling in advanced heart failure. The OCTOPUS-CHF study