1. Articles in category: Velocimetry

    121-144 of 330 « 1 2 ... 3 4 5 6 7 8 9 ... 12 13 14 »
    1. Absolute blood flow measured by optical methods

      Absolute blood flow measured by optical methods
      Absolute blood flow (volume of blood per unit time serving a tissue mass or organ) is a physiological parameter that becomes altered in many diseases. In the retina, blood-flow impairment may occur early in diseases such as glaucoma and diabetic retinopathy. In the brain, cerebral blood-flow loss occurs in conditions such as stroke and Alzheimer's disease. In the kidneys, renal blood flow is a primary factor in acute injury and other nephropathies. Whether a loss of blood flow directly causes cell death or merely reflects a reduction in tissue demand, in vivo blood flow measurements have the potential to ...
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    2. In vivo depth-resolved oxygen saturation by dual-wavelength photothermal (DWP) OCT

      In vivo depth-resolved oxygen saturation by dual-wavelength photothermal (DWP) OCT
      Microvasculature hemoglobin oxygen saturation (SaO2) is important in the progression of various pathologies. Non-invasive depth-resolved measurement of SaO2 levels in tissue microvasculature has the potential to provide early biomarkers and a better understanding of the pathophysiological processes allowing improved diagnostics and prediction of disease progression. We report proof-of-concept in vivo depth-resolved measurement of SaO2 levels in selected 30 µm diameter arterioles in the murine brain using Dual-Wavelength Photothermal (DWP) Optical Coherence Tomography (OCT) with 800 nm and 770 nm photothermal excitation wavelengths. Depth location of back-reflected light from a target arteriole was confirmed using Doppler and speckle contrast OCT images ...
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    3. Higher-order cross-correlation-based Doppler optical coherence tomography

      Higher-order cross-correlation-based Doppler optical coherence tomography

      A method based on higher-order cross-correlation is proposed to fetch the Doppler information on flow velocity within areas under low signal-to-noise ratio (SNR) by spectral domain optical coherence tomography. The proposed method is theoretically developed and validated by measurement of a moving mirror with known velocities. Standard deviations of flow velocities of the mirror under different SNRs are determined by the proposed method and compared with those by the modified phase-resolved method. Measurement of flowing particles within a glass capillary is also conducted, and Doppler flow velocity maps of the glass capillary are reconstructed by both methods. All experimental results ...

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    4. Shear flow-induced optical inhomogeneity of blood assessed in vivo and in vitro by spectral domain optical coherence tomography in the 1.3 um wavelength range

      Shear flow-induced optical inhomogeneity of blood assessed in vivo and in vitro by spectral domain optical coherence tomography in the 1.3 um wavelength range

      The optical inhomogeneity of flowing blood, which appears as a waisted double fan-shaped intensity pattern inside vessels in cross-sectional optical coherence tomography (OCT) images, was investigated for the first time. High resolution spectral domain OCT in the 1.3 μm wavelength region is used to assess this inhomogeneous intravascular backscattering of light in an in vivo mouse model and flow phantom measurements. Based on a predicted alignment of the red blood cells toward laminar shear flow, an angular modulation of the corresponding backscattering cross-section inside the vessels is assumed. In combination with the signal attenuation in depth by absorption and ...

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    5. Feature Of The Week 10/30/11: Medical University of Vienna Researchers Investigate Segmentation of Doppler OCT Signatures Using a Support-Vector Machine

      Feature Of The Week 10/30/11: Medical University of Vienna Researchers Investigate Segmentation of Doppler OCT Signatures Using a Support-Vector Machine
      Researchers from the Medical University of Vienna have been prolific contributors to the field of Optical Coherence Tomography for many years. Their pioneering work started back in the late 1980’s and early 1990’s and the group has published over 165 articles since OCT News started in late 2007 (Reference). Recently the group published interesting work on segmentation of Doppler optical coherence tomography signatures using a support-vector machine. Below is a summary of that work. Analysis of tissue perfusion offers direct access to tissue nutrition, its health, or any pathologic alterations that affect the vascular system. Doppler OCT (DOCT ...
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    6. Using ultrahigh sensitive optical microangiography to achieve comprehensive depth resolved microvasculature mapping for human retina

      Using ultrahigh sensitive optical microangiography to achieve comprehensive depth resolved microvasculature mapping for human retina
      Lin An, Tueng T. Shen, and Ruikang K. Wang This paper presents comprehensive and depth-resolved retinal microvasculature images within human retina achieved by a newly developed ultrahigh sensitive optical microangiography (UHS-OMAG) system. Due to its high flow sensitivity, UHS-OMAG is much more sensitive to tissue motion due to the involun ... [J. Biomed. Opt. 16, 106013 (2011)] published Mon Oct 24, 2011.
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    7. Assessment of strain and strain rate in embryonic chick heart in vivo using tissue Doppler optical coherence tomography

      Assessment of strain and strain rate in embryonic chick heart in vivo using tissue Doppler optical coherence tomography

      We present a method to assess the in vivo radial strain and strain rate of the myocardial wall, which is of great importance to understand the biomechanics of cardiac development, using tissue Doppler optical coherence tomography (tissue-DOCT). Combining the structure and velocity information acquired from tissue-DOCT, the velocity distribution in the myocardial wall is plotted, from which the radial strain and strain rate are evaluated. The results demonstrate that tissue-DOCT can be used as a useful tool to describe tissue deformation, especially, the biomechanical characteristics of the embryonic heart.

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    8. Measurement of cerebral microvascular compliance in a model of atherosclerosis with optical coherence tomography

      Measurement of cerebral microvascular compliance in a model of atherosclerosis with optical coherence tomography
      Optical coherence tomography (OCT) has recently been used to produce 3D angiography of microvasculature and blood flow maps of large vessels in the rodent brain in-vivo. However, use of this optical method for the study of cerebrovascular disease has not been fully explored. Recent developments in neurodegenerative diseases has linked common cardiovascular risk factors to neurodegenerative risk factors hinting at a vascular hypothesis for the development of the latter. Tools for studying cerebral blood flow and the myogenic tone of cerebral vasculature have thus far been either highly invasive or required ex-vivo preparations therefore not preserving the delicate in-vivo conditions ...
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    9. Hemoglobin contrast in magneto-motive optical doppler tomography, optical coherence tomography, and ultrasound imaging methods and apparatus

      Hemoglobin contrast in magneto-motive optical doppler tomography, optical coherence tomography, and ultrasound imaging methods and apparatus
      A novel contrast mechanism for imaging blood flow using magneto-motive optical Doppler tomography (MM-ODT), Optical Coherence Tomography, and Ultrasound. MM-ODT, OCT, and ultrasound combined with an externally applied temporally oscillating high-strength magnetic field detects erythrocytes moving according to the field gradient.
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    10. Vanderbilt University Receives NIH Grant for Functional OCT for Monitoring Drug Resistance in Cancer

      Vanderbilt University Receives NIH Grant for Functional OCT for Monitoring Drug Resistance in Cancer
      Vanderbilt University received a $240,321 2011 NIH grant to investigate functional optical coherence tomography for monitoring drug resistance in cancer. This is part of a multiyear project that started in 2010 and ends in 2013. The principal investigator is Melissa Skala.  Below is a summary of that work. Molecular signaling is a critical therapeutic target in cancer, and molecular therapeutics have achieved some success in treating a variety of cancers. However, our incomplete knowledge of pharmacodynamic effects in vivo limits the success of these molecular therapies. We have recently developed a new molecular imaging technique, photothermal optical coherence tomography ...
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    11. Optical microangiography provides an ability to monitor responses of cerebral microcirculation to hypoxia and hyperoxia in mice

      Optical microangiography provides an ability to monitor responses of cerebral microcirculation to hypoxia and hyperoxia in mice
      In vivo imaging of microcirculation can improve our fundamental understanding of cerebral microhemodynamics under various physiological challenges, such as hypoxia and hyperoxia. However, existing techniques often involve the use of invasive procedures or exogenous contrast agents, which would inevitably perturb the intrinsic physiologic responses of microcirculation being investigated. We report ultrahigh sensitive optical microangiography (OMAG) for label-free monitoring of microcirculation responses challenged by oxygen inhalation. For the first time, we demonstrate that OMAG is capable of showing the impact of acute hypoxia and hyperoxia on microhemodynamic activities, including the passive and active modulation of microvascular density and flux regulation, within ...
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    12. New Diagnostic Imaging Technologies in Nonvariceal Upper Gastrointestinal Bleeding

      New Diagnostic Imaging Technologies in Nonvariceal Upper Gastrointestinal Bleeding
      This article covers new endoscopic imaging modalities in nonvariceal upper gastrointestinal bleeding, such as Doppler ultrasound probe technology, endoscopic ultrasonography, color Doppler optical coherence tomography, and magnification endoscopy. A more in-depth discussion of these modalities and the published evidence supporting their use are included. Furthermore, the shift in focus from identification of conventional visual surface stigmata of recent hemorrhage to an assessment and understanding of subsurface blood flow as it relates to the bleeding lesion is discussed.
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    13. In vivo, label-free, three-dimensional quantitative imaging of kidney microcirculation using Doppler optical coherence tomography

      In vivo, label-free, three-dimensional quantitative imaging of kidney microcirculation using Doppler optical coherence tomography
      Doppler optical coherence tomography (DOCT) is a functional extension of optical coherence tomography (OCT) and is currently being employed in several clinical arenas to quantify blood flow in vivo. In this study, the objective was to investigate the feasibility of DOCT to image kidney microcirculation, specifically, glomerular blood flow. DOCT is able to capture three-dimensional (3D) data sets consisting of a series of cross-sectional images in real time, which enables label-free and non-destructive quantification of glomerular blood flow. The kidneys of adult, male Munich–Wistar rats were exposed through laparotomy procedure after being anesthetized. Following exposure of the kidney beneath ...
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    14. Ultrahigh sensitive optical microangiography reveals depth-resolved microcirculation and its longitudinal response to prolonged ischemic event within skeletal muscles in mice

      Ultrahigh sensitive optical microangiography reveals depth-resolved microcirculation and its longitudinal response to prolonged ischemic event within skeletal muscles in mice
      The primary pathophysiology of peripheral arterial disease is associated with impaired perfusion to the muscle tissue in the lower extremities. The lack of effective pharmacologic treatments that stimulate vessel collateralization emphasizes the need for an imaging method that can be used to dynamically visualize depth-resolved microcirculation within muscle tissues. Optical microangiography (OMAG) is a recently developed label-free imaging method capable of producing three-dimensional images of dynamic blood perfusion within microcirculatory tissue beds at an imaging depth of up to ∼2 mm, with an unprecedented imaging sensitivity of blood flow at ∼4 μm/s. In this paper, we demonstrate the utility ...
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    15. Doppler velocity detection limitations in spectrometer-based versus swept-source optical coherence tomography

      Doppler velocity detection limitations in spectrometer-based versus swept-source optical coherence tomography

      Recent advances in Doppler techniques have enabled high sensitivity imaging of biological flow to measure blood velocities and vascular perfusion. Here we compare spectrometer-based and wavelength-swept Doppler OCT implementations theoretically and experimentally, characterizing the lower and upper observable velocity limits in each configuration. We specifically characterize the washout limit for Doppler OCT, the velocity at which signal degradation results in loss of flow information, which is valid for both quantitative and qualitative flow imaging techniques. We also clearly differentiate the washout effect from the separate phenomenon of phase wrapping. We demonstrate that the maximum detectable Doppler velocity is determined by ...

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    16. Determination of suspension viscosity from the flow velocity profile measured by Doppler Optical Coherence Tomography

      Determination of suspension viscosity from the flow velocity profile measured by Doppler Optical Coherence Tomography
      In this paper we present, for the first time to our knowledge, the experimental results for determining suspension viscosity in a capillary type viscometer from flow velocity profiles measured by Doppler Optical Coherence Tomography. The suspension of 0.3?m polystyrene microspheres in a glycerol-water solution was used as a model fluid. The viscosity of the suspension was controlled by glycerol concentration. The shear rate and the shear stress at the capillary wall were measured at six flow rates. The corresponding viscosities were calculated. The comparison of the measured shear rates with the values calculated according to the flow rate ...
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    17. Flicker-induced changes in retinal blood flow assessed by Doppler optical coherence tomography

      Flicker-induced changes in retinal blood flow assessed by Doppler optical coherence tomography

      We used Doppler Fourier-domain optical coherence tomography (OCT) to investigate flicker-induced changes of total retinal blood flow. Total retinal blood flow was measured by summing flows in veins imaged in double-circular scans around the optic disc. In 3 healthy volunteers, total retinal blood flow was measured before and 10-15 seconds after 30 seconds of flicker stimulation. The average blood flow increased 22.2% (p = 0.002). The total venous and arterial vessel cross-sectional area increased 11.3% (p < 0.001) and +2.7% (p = 0.28) respectively. The average venous and arterial flow velocity were calculated indirectly by dividing total retinal blood flow by total venous and arterial cross-sectional areas. They also increased by 8.8% (p = 0.046) and 18.3% (p = 0.004), respectively. These results show that human retinal blood flow increases after visible flicker stimulation, and this could be measured with OCT.

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    18. Imaging vibrating vocal folds with a high speed 1050 nm swept source OCT and ODT

      Imaging vibrating vocal folds with a high speed 1050 nm swept source OCT and ODT
      Vocal fold vibration is vital in voice production and the correct pitch of speech. We have developed a high speed functional optical coherence tomography (OCT) system with a center wavelength of 1050 nm and an imaging speed of 100,000 A-lines per second. We imaged the vibration of an ex-vivo swine vocal fold. At an imaging speed of 100 frames per second, we demonstrated high quality vocal fold images during vibration. Functional information, such as vibration frequency and vibration amplitude, was obtained by analyzing the tissue surface during vibration. The axial direction velocity distribution in the cross-sectional images of the ...
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    19. Enhanced joint spectral and time domain optical coherence tomography for quantitative flow velocity measurement

      Enhanced joint spectral and time domain optical coherence tomography for quantitative flow velocity measurement
      Recently, a new method called joint spectral and time domain optical coherence tomography (STdOCT) for flow velocity measurement in spectral domain OCT (SD OCT) was presented. This method analyzes the detected timeresolved interference fringe spectra by using a two-dimensional fast Fourier transformation (2D FFT) to determine directly the Doppler frequency shift instead of calculating the phase difference at each depth position of adjacent A-scans. There, it was found that STdOCT is more robust for measurements with low signal to noise ratio than the classic phase-resolved Doppler OCT (DOCT) making it attractive first for imaging fast flow velocities at which a ...
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    20. Automated extraction of 3D Doppler OCT signatures using a support vector machine

      Automated extraction of 3D Doppler OCT signatures using a support vector machine
      We present a method for the automated extraction of Doppler OCT flow information by using a support vector machine that combines different features for classification. We employ histogram equalization that makes it possible to distinguish vessels from bulk tissue by texture analysis. This method is particularly applicable to settings with significant phase noise as it is more robust to multiple scattering components than simple threshold-based methods.
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    21. Design and development of a galvanometer inspired dual beam optical coherence tomography system for flow velocity quantification of the microvasculature

      Design and development of a galvanometer inspired dual beam optical coherence tomography system for flow velocity quantification of the microvasculature
      This paper reports initial experimentation of a dual beam flow velocity estimation setup based on optical coherence tomography (OCT) for biomedical applications. The proposed work incorporates a low cost switching mechanism (rotating galvanometer mirror) for optical signal discrimination between adjacent fiber channels enabling quasisimultaneous multiple specimen scanning. A cascaded interferometric design is used with two sample output arms orientated in parallel to eachother. A cross-correlation computation between these two parallel sample beams yields a relative time delay, enabling assessment and quantification of flow velocities.
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    22. Intensity-based modified Doppler variance algorithm: application to phase instable and phase stable optical coherence tomography systems

      Intensity-based modified Doppler variance algorithm: application to phase instable and phase stable optical coherence tomography systems
      The traditional phase-resolved Doppler method demonstrates great success for in-vivo imaging of blood flow and blood vessels. However, the phase-resolved method always requires high phase stability of the system. In phase instable situations, the performance of the phase-resolved methods will be degraded. We propose a modified Doppler variance algorithm that is based on the intensity or amplitude value. Performances of the proposed algorithm are compared with traditional phase-resolved Doppler variance and color Doppler methods for both phase stable and phase instable systems. For the phase instable situation, the proposed algorithm demonstrates images without phase instability induced artifacts. In-vivo imaging of ...
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    23. Principal-component-analysis-based estimation of blood flow velocities using optical coherence tomography intensity signals

      Principal-component-analysis-based estimation of blood flow velocities using optical coherence tomography intensity signals
      The intensity signal in optical coherence tomography contains information about the translational velocity of scatterers, and can be used to quantify blood flow. We apply principal component analysis to efficiently extract this information. We also study use of nonuniform temporal sampling of the intensity signal to increase the range of quantifiable flow velocities. We demonstrate this technique in simulation, phantom and in vivo blood flow measurements, and highlight its potential to enable three-dimensional wide-field mapping of blood flow using OCT.
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    24. Total retinal blood flow measurement with ultrahigh speed swept source/Fourier domain OCT

      Total retinal blood flow measurement with ultrahigh speed swept source/Fourier domain OCT

      Doppler OCT provides depth-resolved information on flow in biological tissues. In this article, we demonstrate ultrahigh speed swept source/Fourier domain OCT for visualization and quantitative assessment of retinal blood flow. Using swept laser technology, the system operated in the 1050-nm wavelength range at a high axial scan rate of 200 kHz. The rapid imaging speed not only enables volumetric imaging with high axial scan densities, but also enables measurement of high flow velocities in the central retinal vessels. Deep penetration in the optic nerve and lamina cribrosa was achieved by imaging at 1-µm wavelengths. By analyzing en-face images extracted ...

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    121-144 of 330 « 1 2 ... 3 4 5 6 7 8 9 ... 12 13 14 »
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