1. Articles in category: Velocimetry

    1-24 of 344 1 2 3 4 ... 13 14 15 »
    1. Simultaneous Investigation of Vascular and Retinal Pigment Epithelial Pathologies of Exudative Macular Diseases by Multi-Functional Optical Coherence Tomography

      Simultaneous Investigation of Vascular and Retinal Pigment Epithelial Pathologies of Exudative Macular Diseases by Multi-Functional Optical Coherence Tomography

      Purpose: To investigate exudative macular disease, multi-functional optical coherence tomography (MF-OCT) using a 1-μm probe band was developed. The clinical utility of MF-OCT was examined in a descriptive case series. Methods: Ten eyes of nine subjects with exudative macular disease, including one eye with age-related macular degeneration (AMD), one eye with idiopathic neovascular maculopathy, and eight eyes with polypoidal choroidal vasculopathy (PCV), were investigated. Areas of 6 × 6 mm 2 around the pathologic region were scanned with 512 × 1024 depth scans in 6.6 seconds. Structural OCT, Doppler optical coherence angiography (OCA) and cumulative phase retardation images were obtained ...

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    2. Doppler optical coherence tomography for microcirculation studies (Thesis)

      Doppler optical coherence tomography for microcirculation studies (Thesis)

      This thesis forms part of an ongoing long-term project to investigate the suitability of Doppler optical coherence tomography (OCT) as a measurement tool to investigate skin thickness and blood flow in patients with systemic sclerosis. There is a discussion of the characterisation of an electro-optic phase modulator for use in a Doppler OCT imaging system which is being built for the purpose of clinical studies. In addition to this the development of software for the same system is described. The work includes a comparison of two methods of obtaining Doppler information that were tested with the system; a phase resolved ...

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    3. REAL-TIME 3D AND 4D Fourier Domain Doppler Optical Coherence Tomography System

      REAL-TIME 3D AND 4D Fourier Domain Doppler Optical Coherence Tomography System

      An optical coherence tomography imaging system includes a Fourier domain optical coherence tomography sensor system, a signal processing system configured to communicate with the Fourier domain optical coherence tomography sensor system to receive detection signals therefrom and to provide imaging signals, and an image display system configured to communicate with the signal processing system to receive the imaging signals. The signal processing system includes a parallel processor configured to calculate structure information and Doppler information from the detection signals in real time such that the imaging signals provide a real time display of combined structure and flow of an object ...

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    4. Implementation and characterization of phase-resolved Doppler optical coherence tomography method for flow velocity measurement

      Implementation and characterization of phase-resolved Doppler optical coherence tomography method for flow velocity measurement

      In this work, the system implementation and characterization of a Phase-Resolved Doppler Optical Coherence Tomography (PR-DOCT) is presented. The phase-resolved Doppler technique was implemented on a custom built Frequency Domain OCT (FD-OCT) that was recently developed at Suranaree University of Technology. Utilizing Doppler phase changed relation in a complex interference signal caused by moving samples, PR-DOCT can produce visualization and characterization of flow activity such as blood flow in biological samples. Here we report the performance of the implemented PR-DOCT system in term of the Velocity Dynamic Range (VDR), which is defined by the range from the minimum to the ...

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      Mentions: Panomsak Meemon
    5. Method and apparatus for quantitative imaging of blood perfusion in living tissue

      Method and apparatus for quantitative imaging of blood perfusion in living tissue

      Embodiments provide methods and systems for quantitative imaging of blood perfusion in living tissue. A method provides for obtaining an optical microangiography (OMAG) image of a sample, wherein the image has an OMAG background sample; digitally reconstructing a homogeneous ideal static background tissue; replacing the OMAG background sample with the digitally reconstructed homogeneous ideal static background tissue; correlating two or more neighboring A-lines with the digitally reconstructed homogeneous ideal static background tissue; and measuring a phase difference between the two or more neighboring A-lines to quantify blood perfusion in the sample. Methods using digital reconstruction to reduce random phase noise ...

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    6. New insight into rheology and flow properties of complex fluids with Doppler optical coherence tomography

      New insight into rheology and flow properties of complex fluids with Doppler optical coherence tomography

      Flow properties of complex fluids such as colloidal suspensions, polymer solutions, fiber suspensions and blood have a vital function in many technological applications and biological systems. Yet, the basic knowledge on their properties is inadequate for many practical purposes. One important reason for this has been the lack of effective experimental methods that would allow detailed study of the flow behavior of especially opaque multi-phase fluids. Optical Coherence Tomography (OCT) is an emerging technique capable of simultaneous measurement of the internal structure and motion of most opaque materials, with resolution in the micrometer scale and measurement frequency up to 100 ...

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    7. Measurement of elastic wave propagation velocity near tissue surface by optical coherence tomographyand laser Doppler velocimetry

      Measurement of elastic wave propagation velocity near tissue surface by optical coherence tomographyand laser Doppler velocimetry

      We demonstrate a new technique for measuring the velocity of elastic waves propagating near a tissue surface by swept-source optical coherence tomography (OCT). We establish a theory for estimating the elastic wave velocity from the OCT images taken with a slow mechanical scanning, which is experimentally verified using agar and tissue samples. The elastic wave velocity measured by this technique agrees well with previous results and that measured with a laser Doppler velocimeter. We also carry out some trial measurements of the elastic wave velocities of several tissue samples by this method.

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    8. New technique analyses blood flow in glaucoma patients

      New technique analyses blood flow in glaucoma patients

      The link between blood flow in the retina and the development of glaucoma can now be measured accurately for the first time. This was made possible by the further development of an established measurement method, optical coherence tomography (OCT), which enables the visual assessment of the retina and has thus become an important diagnostic tool. It does not, however, provide any information about retinal function. With the support of the Austrian Science Fund FWF, a research team at the Medical University of Vienna has succeeded in making a significant improvement to the technique so that it can now also be ...

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    9. OCT in Rare Chorioretinal Diseases

      OCT in Rare Chorioretinal Diseases

      This study will evaluate the total blood flow in the retina and choroid (structures in the back of the eye) by Doppler optical coherence tomography (OCT) and OCT angiography. Angiography is mapping of the blood vessels. The purpose of measuring blood flow in the retina and choroid is to 1.) determine if rare diseases in these structures causes a change in blood flow compared to healthy eyes and 2.) find out if areas of changed blood flow line up with areas of damage that appear on conventional testing.

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    10. Optical coherence tomography microangiography for monitoring the response of vascular perfusion to external pressure on human skin tissue

      Optical coherence tomography microangiography for monitoring the response of vascular perfusion to external pressure on human skin tissue

      Characterization of the relationship between external pressure and blood flow is important in the examination of pressure-induced disturbance in tissue microcirculation. Optical coherence tomography (OCT)-based microangiography is a promising imaging technique, capable of providing the noninvasive extraction of functional vessels within the skin tissue with capillary-scale resolution. Here, we present a feasibility study of OCT microangiography (OMAG) to evaluate changes in blood perfusion in response to externally applied pressure on human skin tissue in vivo . External force is loaded normal to the tissue surface at the nailfold region of a healthy human volunteer. An incremental force is applied step ...

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    11. Optical imaging of intracranial hemorrhages in newborns: modern strategies in diagnostics and direction for future research

      Optical imaging of intracranial hemorrhages in newborns: modern strategies in diagnostics and direction for future research

      Using Doppler optical coherence tomography (DOCT) we study stress-related intracranial hemorrhages (ICHs) in newborn rats. We investigate a masked stage of ICH development that corresponds to the first 4 h after the stress. We show that this period is characterized by significant changes in the diameter of the sagittal vein and the velocity of the cerebral venous blood flow (CVBF). We discuss diagnostic abilities of wavelet-based methods and consider an adaptive technique allowing us to reveal clearest distinctions in the dynamics of CVBF between normal and stressed newborn rats. Finally, we conclude that the venous insufficiency in newborns and a ...

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    12. Single detector-based absolute velocity measurement using spectral domain Doppler optical coherence tomography

      Single detector-based absolute velocity measurement using spectral domain Doppler optical coherence tomography

      We propose an approach for absolute velocity measurement where the use of a beam displacer provides two orthogonal linearly polarized beams to probe the sample simultaneously at two different incidence angles. The approach helps remove the cross talk image and facilitates single detector-based Fourier domain Doppler velocity measurement. The system has been characterized by quantifying absolute flow velocity in a flow phantom.

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    13. Methods for single-pass volumetric bidirectional blood flow imaging spectral domain optical coherence tomography using a modified hilbert transform

      Methods for single-pass volumetric bidirectional blood flow imaging spectral domain optical coherence tomography using a modified hilbert transform

      The present subject matter relates to in vivo volumetric bidirectional blood flow imaging using single-pass flow imaging spectral domain optical coherence tomography. This technique uses a modified Hilbert transform algorithm to separate moving and non-moving scatterers within a depth. The resulting reconstructed image maps the components of moving scatterers flowing into and out of the imaging axis onto opposite image halfplanes, enabling volumetric bidirectional flow mapping without manual segmentation.

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    14. Monitoring the blood coagulation process under various flow conditions with optical coherence tomography

      Monitoring the blood coagulation process under various flow conditions with optical coherence tomography

      Our previous work demonstrated that an optical coherence tomography (OCT) technique was able to characterize the whole blood coagulation process. The 1 / e light penetration depth ( d 1 / e ) derived from the profiles of reflectance versus depth was developed for detecting the whole blood coagulation process in static state. To consider the effect of blood flow, in the present study, d 1 / e versus time from the coagulating porcine blood circulated in a mock flow loop with various steady laminar flows at mean flow speed in the range from 5 to 25     mm / s . The variation of d 1 / e ...

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    15. Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

      Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

      A novel full-range Fourier domain Doppler optical coherence tomography (full-range FD-DOCT) using sinusoidal phase modulation for B-M scan is proposed. In this sinusoidal B-M scan, zero optical path difference (OPD) position does not move corresponding to lateral scanning points in contrast to linear B-M scan. Since high phase sensitivity arises around the zero OPD position, the proposed full-range FD-DOCT can achieve easily high velocity sensitivity without mirror image around the zero OPD position. Velocity sensitivity dependent on the OPD and the interval of scanning points is examined, and flow velocity detection capability is verified through Doppler imaging of a flow ...

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    16. In vivo OCT microangiography of rodent iris

      In vivo OCT microangiography of rodent iris

      We report on the functional optical coherence tomography (OCT) imaging of iris tissue morphology and microcirculation in living small animals. Anterior segments of healthy mouse and rat eyes are imaged with high-speed spectral domain OCT (SD-OCT) utilizing ultrahigh sensitive optical microangiography (UHS-OMAG) imaging protocol. 3D iris microvasculature is produced by the use of an algorithm that calculates absolute differences between the amplitudes of the OCT interframes. We demonstrate that the UHS-OMAG is capable of delineating iris microvascular beds in the mouse and rat with capillary-level resolution. Furthermore, the fast imaging speed enables dynamic imaging of iris micro-vascular response during drug-induced ...

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    17. Georgetown University Receives NIH Grant for Non-Invasive Evaluation of Transplant Kidney Using OCT

      Georgetown University Receives NIH Grant for Non-Invasive Evaluation of Transplant Kidney Using OCT

      Georgetown University Received at 2014 NIH Grant for $520,754 for Non-Invasive Evaluation of Transplant Kidney Using OCT. The principal investigator is Peter Michael Andrewss. The program began in 2014 and ends in 2018. Below is a summary of the proposed work. There is currently a worldwide shortage of kidneys for transplantation due mainly to the fact that there is no reliable means to determine their viability (i.e., kidneys stored for long periods of time, etc.). Also, following transplantation, kidneys oftn do not function immediately and their status is unclear. Previously, we have shown that the histopathology of living ...

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    18. Doppler Optical Coherence Tomography

      Doppler Optical Coherence Tomography

      Optical Coherence Tomography (OCT) has revolutionized ophthalmology. Since its introduction in the early 1990s it has continuously improved in terms of speed, resolution and sensitivity. The technique has also seen a variety of extensions aiming to assess functional aspects of the tissue in addition to morphology. One of these approaches is Doppler OCT (DOCT), which aims to visualize and quantify blood flow. Such extensions were already implemented in time domain systems, but have gained importance with the introduction of Fourier domain OCT. Nowadays phase-sensitive detection techniques are most widely used to extract blood velocity and blood flow from tissues. A ...

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    19. High speed, wide velocity dynamic range Doppler optical coherence tomography (Part IV): split spectrum processing in rotary catheter probes

      High speed, wide velocity dynamic range Doppler optical coherence tomography (Part IV): split spectrum processing in rotary catheter probes

      We report a technique for blood flow detection using split spectrum Doppler optical coherence tomography (ssDOCT) that shows improved sensitivity over existing Doppler OCT methods. In ssDOCT, the Doppler signal is averaged over multiple sub-bands of the interferogram, increasing the SNR of the Doppler signal. We explore the parameterization of this technique in terms of number of sub-band windows, width and overlap of the windows, and their effect on the Doppler signal to noise in a flow phantom. Compared to conventional DOCT, ssDOCT processing has increased flow sensitivity. We demonstrate the effectiveness of ssDOCT in-vivo for intravascular flow detection within ...

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    20. University of Miami Receives NIH Grant for Advanced Imaging for Diabetic Retinopathy

      University of Miami Receives NIH Grant for Advanced Imaging for Diabetic Retinopathy

      The University of Miami Received a 2014 NIH Grant for $367,808 for Advanced Imaging for Diabetic Retinopathy. The principal investigator is Delia Cabrera Debuc. The program began in 2011 and ends in 2016. Below is a summary of the proposed work. Diabetic retinopathy (DR) is a major cause of visual loss in diabetic individuals that presents a significant diagnostic challenge. Advances in preventing vision loss in these individuals are hindered by limited understanding of mechanisms underlying DR and the altered relationships between the retinal neural tissue and retinal vasculature. Therefore, an objective test for the early diagnosis and evaluation ...

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    21. Quantitative Optical Coherence Tomography Angiography of Choroidal Neovascularization in Age-related Macular Degeneration

      Quantitative Optical Coherence Tomography Angiography of Choroidal Neovascularization in Age-related Macular Degeneration

      Purpose To detect and quantify choroidal neovascularization (CNV) in patients with age-related macular degeneration (AMD) using optical coherence tomography (OCT) angiography. Design Observational, cross-sectional study. Participants A total of 5 normal subjects and 5 subjects with neovascular AMD were included. Methods A total of 5 eyes with neovascular AMD and 5 normal age-matched controls were scanned by a high-speed (100 000 A-scans/seconds) 1050-nm wavelength swept-source OCT. The macular angiography scan covered a 3×3-mm area and comprised 200×200×8 A-scans acquired in 3.5 seconds. Flow was detected using the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. Motion artifacts were ...

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    22. Feature Of The Week 3/23/14: Tambov State Technical University Investigates One Specific Velocity Color Mapping One Specific Velocity Color Mapping

      Feature Of The Week 3/23/14: Tambov State Technical University Investigates One Specific Velocity Color Mapping One Specific Velocity Color Mapping

      The method of sign-sensitive mapping of the given range of velocities in a flow with complex geometry based on the principles of optical coherence tomography is described. To produce an alternating-sign flow, the 1% aqueous intralipid solution and the tilted capillary entry with the contraction coefficient 4:1 are used. The mapping is controlled using two parameters, the value of one specific velocity (OSV) for mapping and the accuracy of its determination. The structure image and two OSV images (for positive and negative direction of motion) are obtained as a result of selecting and processing the relevant parts of the ...

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    23. Maximum Likelihood Doppler Frequency Estimation under Decorrelation Noise for Quantifying Flow in Optical Coherence Tomography

      Maximum Likelihood Doppler Frequency Estimation under Decorrelation Noise for Quantifying Flow in Optical Coherence Tomography

      Recent hardware advances in optical coherence tomography (OCT) have led to ever higher A-scan rates. However, the estimation of blood flow axial velocities is limited by the presence and type of noise. Higher acquisition rates alone do not necessarily enable precise quantification of Doppler velocities, particularly if the estimator is sub-optimal. In previous work, we have shown that the Kasai autocorrelation estimator is statistically sub-optimal under conditions of additive white Gaussian noise. In addition, for practical OCT measurements of flow, decorrelation noise affects Doppler frequency estimation by broadening the signal spectrum. Here we derive a general maximum likelihood estimator (MLE ...

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    24. Real-time stroboscopic full-field optical coherence tomography based on graphics processing unit

      Real-time stroboscopic full-field optical coherence tomography based on graphics processing unit

      We present the real-time stroboscopic full-field optical coherence tomography (FF-OCT) system that is based on graphics processing unit (GPU). The basic configuration of the proposed FF-OCT system was the Linnik interferometer. While scanning of a reference mirror in the axial direction, a series of the transverse sectional image was captured with a 2-dimensional CCD camera. To get a depth-resolved 3-D image, the light source of OCT was turned on and off like a stroboscope at the Doppler frequency of the OCT system. The CCD camera used in experiment operated at a rate of 200 frames per second, but the Doppler ...

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    1-24 of 344 1 2 3 4 ... 13 14 15 »
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