1. Articles in category: Velocimetry

    121-144 of 345 « 1 2 ... 3 4 5 6 7 8 9 ... 13 14 15 »
    1. Visualization and measurement of capillary-driven blood flow using spectral domain optical coherence tomography

      Visualization and measurement of capillary-driven blood flow using spectral domain optical coherence tomography

      Capillary-driven flow (CD-flow) in microchannels plays an important role in many microfluidic devices. These devices, the most popular being those based in lateral flow, are becoming increasingly used in health care and diagnostic applications. CD-flow can passively pump biological fluids as blood, serum or plasma, in microchannels and it can enhance the wall mass transfer by exploiting the convective effects of the flow behind the meniscus. The flow behind the meniscus has not been experimentally identified up to now because of the lack of high-resolution, non-invasive, cross-sectional imaging means. In this study, spectral-domain Doppler optical coherence tomography is used to ...

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    2. OCT methods for capillary velocimetry

      OCT methods for capillary velocimetry

      To date, two main categories of OCT techniques have been described for imaging hemodynamics: Doppler OCT and OCT angiography. Doppler OCT can measure axial velocity profiles and flow in arteries and veins, while OCT angiography can determine vascular morphology, tone, and presence or absence of red blood cell (RBC) perfusion. However, neither method can quantify RBC velocity in capillaries, where RBC flow is typically transverse to the probe beam and single-file. Here, we describe new methods that potentially address these limitations. Firstly, we describe a complex-valued OCT signal in terms of a static scattering component, dynamic scattering component, and noise ...

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    3. Doppler streak mode Fourier domain optical coherence tomography

      Doppler streak mode Fourier domain optical coherence tomography

      Doppler Fourier domain optical coherence tomography is able to be used for in vivo blood flow measurement. In conventional methods, the highest velocity that can be measured is limited to the range the phase shift between two successively recorded depth profiles at the same probe-beam location, which cannot exceed (-π, π), otherwise phase wrapping will occur. This phase-wrapping limit is determined by the time interval between two consecutive A-scans. We present a novel approach to shorten the time interval between two consecutive A-scans and thus increase the phase-wrapping limit by using an area scan camera to record the interference spectrum ...

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    4. Label-free 3D imaging of microstructure, blood, and lymphatic vessels within tissue beds in vivo

      Label-free 3D imaging of microstructure, blood, and lymphatic vessels within tissue beds in vivo

      This Letter reports the use of an ultrahigh resolution optical microangiography (OMAG) system for simultaneous 3D imaging of microstructure and lymphatic and blood vessels without the use of an exogenous contrast agent. An automatic algorithm is developed to segment the lymphatic vessels from the microstructural images based on the fact that the lymph fluid is optically transparent. An OMAG system is developed that utilizes a broadband supercontinuum light source, providing an axial resolution of 2.3 μm and lateral resolution of 5.8 μm, capable of resolving the capillary vasculature and lymphatic vessels innervating microcirculatory tissue beds. Experimental demonstration is ...

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    5. Feasibiliy of optical detection of soft tissue deformation during needle insertion

      Feasibiliy of optical detection of soft tissue deformation during needle insertion

      Needles provide an effective way to reach lesions in soft tissue and are frequently used for diagnosis and treatment. Examples include biopsies, tumor ablation, and brachytherapy. Yet, precise localization of the needle with respect to the target is complicated by motion and deformation of the tissue during insertion. We have developed a prototypical needle with an embedded optical fiber allowing to obtain optical coherence tomography images of the tissue in front of the needle tip. Using the data and particularly the Doppler information it is possible to estimate the motion of the needle tip with respect to the surrounding soft ...

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    6. Dual-beam optical coherence tomography system for quantification of flow velocity in capillary phantoms

      Dual-beam optical coherence tomography system for quantification of flow velocity in capillary phantoms

      The quantification of (blood) flow velocity within the vasculature has potent diagnostic and prognostic potential. Assessment of flow irregularities in the form of increased permeability (micro haemorrhaging), the presence of avascular areas, or conversely the presence of vessels with enlarged or increased tortuosity in the acral regions of the body may provide a means of non-invasive in vivo assessment. If assessment of dermal flow dynamics were performed in a routine manner, the existence and prevalence of ailments such as diabetes mellitus, psoriatic arthritis and Raynaud's condition may be confirmed prior to clinical suspicion. This may prove advantageous in cases ...

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    7. Microfluidics analysis of blood using joint spectral and time domain optical coherence tomography

      Microfluidics analysis of blood using joint spectral and time domain optical coherence tomography

      Although the Doppler Optical Coherence Tomography techniques have already enabled imaging of blood flow in large vessels in biological tissues, the generation of velocity maps of the capillary network is still a challenge. Since several important physiological and pathological phenomena occur in the microcirculation, the possibility of flow imaging and velocity assessment in microcapillaries may be important for medical diagnostics. Understanding of the origin of the Doppler signal in capillary vessels and limitations of such measurements is essential for further development of Doppler OCT methods. In the OCT flow maps of a microcapillary network randomly varying Doppler signals are observed ...

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    8. Split-spectrum amplitude-decorrelation angiography with optical coherence tomography

      Split-spectrum amplitude-decorrelation angiography with optical coherence tomography

      Amplitude decorrelation measurement is sensitive to transverse flow and immune to phase noise in comparison to Doppler and other phase-based approaches. However, the high axial resolution of OCT makes it very sensitive to the pulsatile bulk motion noise in the axial direction. To overcome this limitation, we developed split-spectrum amplitude-decorrelation angiography (SSADA) to improve the signal-to-noise ratio (SNR) of flow detection. The full OCT spectrum was split into several narrower bands. Inter-B-scan decorrelation was computed using the spectral bands separately and then averaged. The SSADA algorithm was tested on in vivo images of the human macula and optic nerve head ...

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    9. 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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    10. Catechin prevents severe dyslipidemia-associated changes in wall biomechanics of cerebral arteries in LDLr-/-:hApoB+/+ mice and improves cerebral blood flow

      Catechin prevents severe dyslipidemia-associated changes in wall biomechanics of cerebral arteries in LDLr-/-:hApoB+/+ mice and improves cerebral blood flow
      Endothelial dysfunction and oxidative stress contribute to the atherosclerotic process that includes stiffening of large peripheral arteries. In contrast, we previously reported a paradoxical increase in cerebrovascular compliance in LDLr-/-: hApoB+/+ atherosclerotic (ATX) mice. We hypothesized that prevention of cerebral artery endothelial function with a chronic dietary antioxidant intake would normalize the changes in cerebral artery wall structure and biomechanics and prevent the decline in basal cerebral blood flow (CBF) associated with atherosclerosis. Three-month old ATX mice were treated, or not, for 3 months with the polyphenol (+)-catechin (CAT, 30 mg/kg/day) and compared to wild-type (WT) controls. In ...
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    11. High-penetration swept source Doppler optical coherence angiography by fully numerical phase stabilization

      High-penetration swept source Doppler optical coherence angiography by fully numerical phase stabilization
      A high-penetration swept-source optical coherence tomography (HP-SS-OCT) system based on a 1-μm short cavity laser is developed. Doppler OCT processing is applied, along with a custom-made numerical phase stabilization algorithm; this process does not require additional calibration hardware. Thus, our phase stabilization method is simple and can be employed in a variety of SS-OCT systems. The bidirectional blood flow and vasculature in the deep choroid was successfully imaged via two Doppler modes that use different time intervals for Doppler processing. En face projection image of squared power of Doppler shift is compared to ICGA, and the utility of our method ...
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    12. Dual-beam-scan Doppler optical coherence angiography for birefringence-artifact-free vasculature imaging

      Dual-beam-scan Doppler optical coherence angiography for birefringence-artifact-free vasculature imaging
      Dual-beam-scan Doppler optical coherence angiography (DB-OCA) enables high-speed, high-sensitivity blood flow imaging. However, birefringence of biological tissues is an obstacle to vasculature imaging. Here, the influence of polarization and birefringence on DB-OCA imaging was analyzed. A DB-OCA system without birefringence artifact has been developed by introducing a Faraday rotator. The performance was confirmed in vitro using chicken muscle and in vivo using the human eye. Birefringence artifacts due to birefringent tissues were suppressed. Micro-vasculatures in the lamina cribrosa and nerve fiber layer of human eyes were visualized in vivo. High-speed and high-sensitivity micro-vasculature imaging involving birefringent tissues is available with ...
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    13. Congratulations to Chia-Pin Liang From the University of Maryland a Winner of a 2012 Student Travel Grant Award

      Congratulations to Chia-Pin Liang From the University of Maryland a Winner of a 2012 Student Travel Grant Award
      Chia-Pin Liang from the University of Maryland is one of four winners of the OCT News 2012 student travel grant awards (see prior announcement Here). Below is a summary of his work. Stereotactic procedures that require insertion of needle-based instruments into the brain serve important roles in a variety of neurosurgical interventions such as biopsy, catheterization, and electrode placement. The laceration of blood vessels in the path of the advancing needle can result in stroke and even death and is perhaps the most worried complication. Also, the brain may shift during surgery because of cerebrospinal fluid (CSF) leakage so that ...
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    14. A forward-imaging needle-type OCT probe for image guided stereotactic procedures

      A forward-imaging needle-type OCT probe for image guided stereotactic procedures
      A forward-imaging needle-type optical coherence tomography (OCT) probe with Doppler OCT (DOCT) capability has the potential to solve critical challenges in interventional procedures. A case in point is stereotactic neurosurgery where probes are advanced into the brain based on predetermined coordinates. Laceration of blood vessels in front of the advancing probe is an unavoidable complication with current methods. Moreover, cerebrospinal fluid (CSF) leakage during surgery can shift the brain rendering the predetermined coordinates unreliable. In order to address these challenges, we developed a forward-imaging OCT probe (740 μm O.D.) using a gradient-index (GRIN) rod lens that can provide real-time ...
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    15. Cocaine-induced cortical microischemia in the rodent brain: clinical implications

      Cocaine-induced cortical microischemia in the rodent brain: clinical implications
      Cocaine-induced stroke is among the most serious medical complications associated with its abuse. However, the extent to which acute cocaine may induce silent microischemia predisposing the cerebral tissue to neurotoxicity has not been investigated; in part, because of limitations of current neuroimaging tools, that is, lack of high spatiotemporal resolution and sensitivity to simultaneously measure cerebral blood flow (CBF) in vessels of different calibers (including capillaries) quantitatively and over a large field of view. Here we combine ultrahigh-resolution optical coherence tomography to enable tracker-free three-dimensional (3D) microvascular angiography and a new phase-intensity-mapping algorithm to enhance the sensitivity of 3D optical ...
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    16. 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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    17. 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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    18. 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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    19. 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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    20. 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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    21. 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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    22. 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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    23. 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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    24. 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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    121-144 of 345 « 1 2 ... 3 4 5 6 7 8 9 ... 13 14 15 »
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