1. Articles from David A. Boas

    1-24 of 34 1 2 »
    1. 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
    2. 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
    3. MATLAB code and data processing guide for Dynamic Light Scattering-Optical Coherence Tomography

      MATLAB code and data processing guide for Dynamic Light Scattering-Optical Coherence Tomography

      This guide is for post data processing of DLSOCT, which outputs axial velocity (Vz), transverse velocity (Vx), total velocity(V), the ratio of static component (Ms), the ratio of dynamic component (Mf), and fitting accuracy (R). The speed upper limit is determined by OCT system Aline rate and 3Dvoxel size.

      Read Full Article
    4. 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
    5. 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
    6. 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
    7. 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
    8. 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
    9. 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
    10. 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
    11. 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
    12. 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
    13. 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
    14. 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
    15. 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
    16. Cross-validation of serial optical coherence scanning and diffusion tensor imaging: A study on neural fiber maps in human medulla oblongata

      Cross-validation of serial optical coherence scanning and diffusion tensor imaging: A study on neural fiber maps in human medulla oblongata

      We established a strategy to perform cross-validation of serial optical coherence scanner imaging (SOCS) and diffusion tensor imaging (DTI) on a postmortem human medulla. Following DTI, the sample was serially scanned by SOCS, which integrates a vibratome slicer and a multi-contrast optical coherence tomography rig for large-scale three-dimensional imaging at microscopic resolution. The DTI dataset was registered to the SOCS space. An average correlation coefficient of 0.9 was found between the co-registered fiber maps constructed by fractional anisotropy and retardance contrasts. Pixelwise comparison of fiber orientations demonstrated good agreement between the DTI and SOCS measures. Details of the comparison ...

      Read Full Article
    17. Statistical intensity variation analysis for rapid volumetric imaging of capillary network flux

      Statistical intensity variation analysis for rapid volumetric imaging of capillary network flux

      We present a novel optical coherence tomography (OCT)-based technique for rapid volumetric imaging of red blood cell (RBC) flux in capillary networks. Previously we reported that OCT can capture individual RBC passage within a capillary, where the OCT intensity signal at a voxel fluctuates when an RBC passes the voxel. Based on this finding, we defined a metric of statistical intensity variation (SIV) and validated that the mean SIV is proportional to the RBC flux [RBC/s] through simulations and measurements. From rapidly scanned volume data, we used Hessian matrix analysis to vectorize a segment path of each capillary ...

      Read Full Article
    18. Blockface histology with optical coherence tomography: A comparison with Nissl staining

      Blockface histology with optical coherence tomography: A comparison with Nissl staining

      Spectral domain optical coherence tomography (SD-OCT) is a high resolution imaging technique that generates excellent contrast based on intrinsic optical properties of the tissue, such as neurons and fibers. The SD-OCT data acquisition is performed directly on the tissue block, diminishing the need for cutting, mounting and staining. We utilized SD-OCT to visualize the laminar structure of the isocortex and compared cortical cytoarchitecture with the gold standard Nissl staining, both qualitatively and quantitatively. In histological processing, distortions routinely affect registration to the blockface image and prevent accurate 3D reconstruction of regions of tissue. We compared blockface registration to SD-OCT and ...

      Read Full Article
    19. Multiple-capillary measurement of RBC speed, flux, and density with optical coherence tomography

      Multiple-capillary measurement of RBC speed, flux, and density with optical coherence tomography

      As capillaries exhibit heterogeneous and fluctuating dynamics even during baseline, a technique measuring red blood cell (RBC) speed and flux over many capillaries at the same time is needed. Here, we report that optical coherence tomography can capture individual RBC passage simultaneously over many capillaries located at different depths. Further, we demonstrate the ability to quantify RBC speed, flux, and linear density. This technique will provide a means to monitor microvascular flow dynamics over many capillaries at different depths at the same time.

      Read Full Article
    20. Functional imaging of hemodynamic stimulus response in the rat retina with ultrahigh-speed spectral / Fourier domain OCT

      Functional imaging of hemodynamic stimulus response in the rat retina with ultrahigh-speed spectral / Fourier domain OCT

      Measuring retinal hemodynamics in response to flicker stimulus is important for investigating pathophysiology in small animal models of diabetic retinopathy, because a reduction in the hyperemic response is thought to be one of the earliest changes in diabetic retinopathy. In this study, we investigated functional imaging of retinal hemodynamics in response to flicker stimulus in the rat retina using an ultrahigh speed spectral / Fourier domain OCT system at 840nm with an axial scan rate of 244kHz. At 244kHz the nominal axial velocity range that could be measured without phase wrapping was +/-37.7mm/s. Pulsatile total retinal arterial blood flow ...

      Read Full Article
    21. Quantitative imaging of cerebral blood flow velocity and intracellular motility using dynamic light scattering–optical coherence tomography

      Quantitative imaging of cerebral blood flow velocity and intracellular motility using dynamic light scattering–optical coherence tomography

      This paper describes a novel optical method for label-free quantitative imaging of cerebral blood flow (CBF) and intracellular motility (IM) in the rodent cerebral cortex. This method is based on a technique that integrates dynamic light scattering (DLS) and optical coherence tomography (OCT), named DLS–OCT. The technique measures both the axial and transverse velocities of CBF, whereas conventional Doppler OCT measures only the axial one. In addition, the technique produces a three-dimensional map of the diffusion coefficient quantifying nontranslational motions. In the DLS–OCT diffusion map, we observed high-diffusion spots, whose locations highly correspond to neuronal cell bodies and ...

      Read Full Article
    22. Dynamic light scattering optical coherence tomography

      Dynamic light scattering optical coherence tomography

      We introduce an integration of dynamic light scattering (DLS) and optical coherence tomography (OCT) for high-resolution 3D imaging of heterogeneous diffusion and flow. DLS analyzes fluctuations in light scattered by particles to measure diffusion or flow of the particles, and OCT uses coherence gating to collect light only scattered from a small volume for high-resolution structural imaging. Therefore, the integration of DLS and OCT enables high-resolution 3D imaging of diffusion and flow. We derived a theory under the assumption that static and moving particles are mixed within the OCT resolution volume and the moving particles can exhibit either diffusive or ...

      Read Full Article
    23. Frequency-domain measurement of neuronal activity using dynamic optical coherence tomography

      Frequency-domain measurement of neuronal activity using dynamic optical coherence tomography

      We report preliminary results on high-resolution in vivo imaging of fast intrinsic optical signals of neuronal activity in the frequency domain. An optical coherence tomography (OCT) system was used for dynamic imaging of the cross section of rodent somatosensory cortex at 250 frame/s. Neurons in the cortex were excited by contralateral forepaw stimulation, and the ipsilateral forepaw was stimulated as a control. Hemodynamic responses at the cortical surface, which were simultaneously measured using a CCD, confirmed that forepaw stimulation properly evoked neuronal activation. Analysis of the OCT signal in the frequency domain resulted in that the spectrum significantly increased ...

      Read Full Article
    1-24 of 34 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. (34 articles) David A. Boas
    2. (27 articles) Massachusetts General Hospital
    3. (25 articles) Harvard University
    4. (10 articles) Massachusetts Institute of Technology
    5. (8 articles) Boston University
    6. (8 articles) Vivek J. Srinivasan
    7. (5 articles) Harsha Radhakrishnan
    8. (5 articles) James G. Fujimoto
    9. (5 articles) Hui Wang
    10. (4 articles) Thorlabs
    11. (1 articles) Yamagata University
    12. (1 articles) Bern University of Applied Sciences
    13. (1 articles) Medical University of Vienna
    14. (1 articles) University of Maryland
    15. (1 articles) Koen A. Vermeer
    16. (1 articles) Vishali Gupta
    17. (1 articles) Bernhard Baumann
    18. (1 articles) Brandon J. Lujan
    19. (1 articles) Antonia Lichtenegger
    20. (1 articles) OCTLIGHT
  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 Quantitative cerebral blood flow with Optical Coherence Tomography 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 Hybrid registration of retinal fluorescein angiography and optical coherence tomography images of patients with diabetic retinopathy Optical Coherence Tomography Angiography Quality Across Three Multicenter Clinical Studies of Diabetic Retinopathy The Role of Optical Coherence Tomography Angiography(OCTA) in Detecting Choroidal Neovascularization in DifferentStages of Best Macular Dystrophy: A Case Series