234 results on '"Velocity mapping"'
Search Results
2. Techniques and Clinical Applications of Phase-Contrast MRI in CHD
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Rajeshkannan, Ramiah, Rajeshkannan, Ramiah, editor, Raj, Vimal, editor, and Viswamitra, Sanjaya, editor
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- 2021
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3. Techniques in the Assessment of Cardiovascular Blood Flow and Velocity
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Markl, Michael, Toth, Peter P., Series Editor, Kwong, Raymond Y., editor, Jerosch-Herold, Michael, editor, and Heydari, Bobak, editor
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- 2019
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4. Quantitative measurements of flow dynamics in 3D hoppers using MRI.
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Mehdizad, Maral, Fullard, Luke, Galvosas, Petrik, and Holland, Daniel
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FLOW measurement , *MAGNETIC resonance imaging - Abstract
This work uses a recently developed MRI method to measure the solid fraction and velocity in three-dimensional (3D) hoppers quantitatively. We demonstrate that the measurements are quantitative by calculating the mass flow rate within the hopper using MRI and show good agreement with the mass flow rate measured gravimetrically. We study the velocity and solid fraction in hoppers with various angles and outlet sizes. We show that the solid fraction decreases smoothly from the bulk value above the outlet, indicating that the assumption of a "free-fall arch" used in some mass flow correlations is invalid. Furthermore, we show that the solid fraction, velocity and vertical evolution of the acceleration are all self-similar when normalised by the value at the centre of the outlet in a 3D hopper, in agreement with recent studies of 2D hoppers. Thus, these quantitative measurements enable evaluation of phenomenological models describing the flow rate from hoppers. [Display omitted] • We present quantitative measurements of solid fraction and velocity in 3D hoppers. • The velocity and solid fraction profiles scale with outlet size. • There is no "empty annulus" at the outlet of a hopper. • Acceleration increases towards the outlet and there is no "free fall arch". [ABSTRACT FROM AUTHOR]
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- 2021
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5. Multipoint 5D flow cardiovascular magnetic resonance - accelerated cardiac- and respiratory-motion resolved mapping of mean and turbulent velocities
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Jonas Walheim, Hannes Dillinger, and Sebastian Kozerke
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4D flow MRI ,Velocity mapping ,Turbulent kinetic energy ,Respiratory motion compensation ,Cartesian Golden angle ,Low-rank image reconstruction ,Diseases of the circulatory (Cardiovascular) system ,RC666-701 - Abstract
Abstract Background Volumetric quantification of mean and fluctuating velocity components of transient and turbulent flows promises a comprehensive characterization of valvular and aortic flow characteristics. Data acquisition using standard navigator-gated 4D Flow cardiovascular magnetic resonance (CMR) is time-consuming and actual scan times depend on the breathing pattern of the subject, limiting the applicability of the method in a clinical setting. We sought to develop a 5D Flow CMR framework which combines undersampled data acquisition including multipoint velocity encoding with low-rank image reconstruction to provide cardiac- and respiratory-motion resolved assessment of velocity maps and turbulent kinetic energy in fixed scan times. Methods Data acquisition and data-driven motion state detection was performed using an undersampled Cartesian tiny Golden angle approach. Locally low-rank (LLR) reconstruction was implemented to exploit correlations among heart phases and respiratory motion states. To ensure accurate quantification of mean and turbulent velocities, a multipoint encoding scheme with two velocity encodings per direction was incorporated. Velocity-vector fields and turbulent kinetic energy (TKE) were obtained using a Bayesian approach maximizing the posterior probability given the measured data. The scan time of 5D Flow CMR was set to 4 min. 5D Flow CMR with acceleration factors of 19 .0 ± 0.21 (mean ± std) and velocity encodings (VENC) of 0.5 m/s and 1.5 m/s per axis was compared to navigator-gated 2x SENSE accelerated 4D Flow CMR with VENC = 1.5 m/s in 9 subjects. Peak velocities and peak flow were compared and magnitude images, velocity and TKE maps were assessed. Results While net scan time of 5D Flow CMR was 4 min independent of individual breathing patterns, the scan times of the standard 4D Flow CMR protocol varied depending on the actual navigator gating efficiency and were 17.8 ± 3.9 min on average. Velocity vector fields derived from 5D Flow CMR in the end-expiratory state agreed well with data obtained from the navigated 4D protocol (normalized root-mean-square error 8.9 ± 2.1%). On average, peak velocities assessed with 5D Flow CMR were higher than for the 4D protocol (3.1 ± 4.4%). Conclusions Respiratory-motion resolved multipoint 5D Flow CMR allows mapping of mean and turbulent velocities in the aorta in 4 min.
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- 2019
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6. Experimental Study on Motion Control of Rope-Driven Snake Manipulator Using Velocity Mapping Method.
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Gu, Haiyu, Wei, Cheng, Zhang, Zeming, and Zhao, Yang
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The rope-driven snake manipulator is a bionic mechanism with hyper redundant DOFs and can be applied in narrow and confined environments, such as surgery, spacecraft, nuclear plant, etc. The kinematic mapping expressed by the rope length, joint angle and end pose is highly nonlinear and difficult to be calculated. Moreover, the control methods with rope length as input are prone to redundant driving ropes getting stuck due to differences in model and actual mechanism. Therefore, the perfect kinematic mapping of the rope-driven snake manipulator is necessary for designing high-efficiency motion controllers. In this paper, an analytical mapping about the velocities of ropes, joints and end is established and verified. Firstly, a prototype inspired by the biological snake spine is designed. And then the Jacobian matrix representing the velocity mapping is derived and analyzed in detail. The joint and rope velocities are optimized by configuring the null space vector of the Jacobian matrix. Based on the velocity mapping and optimization, a motion control scheme for the snake manipulator is established to realize servo control of the joints and end. Finally, the trajectory tracking simulation and experiment are executed to verify the velocity mapping theory and control scheme. This research can provide solutions for the complex motion control problems of subsequent snake manipulators. [ABSTRACT FROM AUTHOR]
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- 2020
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7. Impact of microplastics on organic fouling of hollow fiber membranes
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Ghasemi, Sahar, Yan, Bin, Zargar, Masoumeh, Ling, Nicholas N.A., Fridjonsson, Einar O., Johns, Michael L., Ghasemi, Sahar, Yan, Bin, Zargar, Masoumeh, Ling, Nicholas N.A., Fridjonsson, Einar O., and Johns, Michael L.
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Given the potential hazards of microplastics (MPs), it is desirable to efficiently remove them during wastewater treatment processes. To this end, ultrafiltration (UF) membranes can significantly increase the removal of MPs, however the fouling of such membrane modules can also be impacted by the presence of MPs. Magnetic Resonance Imaging (MRI) was used here to non-invasively quantify the effect of polyethylene (PE) MPs accumulation in a 3D UF hollow fiber (HF) membrane module containing 400 fibers, via direct non-invasive velocity imaging of the flow distribution between individual fibers during module operation. The co-effect of MPs and alginate (a common organic model foulant mimicking extracellular polymeric substances (EPS)) on fouling of the HF module was then explored. Flow was initially equally distributed with fouling causing flow in particular fibers to be significantly reduced. Fouling with MPs resulted in minimal flow distribution disruption and was easily remediated hydraulically, in contrast alginate fouling required chemical cleaning in order to fully restore homogeneous flow distribution between the fibers. The presence of both MPs and alginate resulted in a more heterogeneous disruption of the fibre flow distribution due to fouling and resulted in much more effective hydraulic cleaning of the module.
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- 2023
8. Special Pulse Sequences for Cardiac Imaging
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Ridgway, John P., Plein, Sven, editor, Greenwood, John, editor, and Ridgway, John P., editor
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- 2015
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9. Gas and Liquid Phase Imaging of Foam Flow Using Pure Phase Encode Magnetic Resonance Imaging
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Alexander Adair, Sebastian Richard, and Benedict Newling
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foam flow ,magnetic resonance imaging ,velocity mapping ,pipe flow ,two-phase flow ,Organic chemistry ,QD241-441 - Abstract
Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented in this article focuses on the use of MRI to measure density and velocity of foam as it passes through a pipe constriction. The foam was created by bubbling fluorinated gas through an aqueous solution. This allowed for the liquid and gas phases to be measured separately by probing the 1H and 19F behavior of the same foam. Density images and velocity maps of the gas and liquid phases of foam flowing through a pipe constriction are presented. In addition, results of computational fluid dynamics simulations of foam flow in the pipe constriction are compared with experimental results.
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- 2020
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10. General Principles of Cardiac Magnetic Resonance Imaging
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Fogel, Mark A., Syed, Mushabbar A., editor, and Mohiaddin, Raad H., editor
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- 2012
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11. Advances in NMR and MRI of Materials.
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Serša, Igor and Serša, Igor
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Chemistry ,Research & information: general ,13-interval PGSTE ,22R and 22S epimers ,2D NMR ,3-Tau model ,CPMG ,CTAB ,Fast Field Cycling ,HPLC ,Inverse Laplace Transform ,Ionic liquids ,L-Curve regularization ,MAS ,NMR ,NMR diffusometry ,NMR relaxometry ,PGSE ,PVC ,Rouse ,VXC72 carbon black ,ZSM-5 ,[Pyr13][Tf2N] ,[Pyr16][Tf2N] ,accelerator ,accelerators ,accuracy ,anisotropy ,archaeological wood ,asphaltenes ,autocatalytic reaction ,beech (Fagus sylvatica) ,biomolecules ,biorelevant dynamic conditions ,budesonide ,calorimetry ,carthamin-3'potassium salt ,cement hydration ,chemical reactivity ,conductivity tensor imaging (CTI) ,confined liquid ,diffusion ,diffusion tensor imaging (DTI) ,diffusion-NMR ,dipolar echoes ,drug delivery system ,drug release ,drying process ,dysprosium ,electrical conductivity ,epoxy resin ,erbium ,fast relaxation times ,fermented safflower petal tablet ,flip angle ,foam flow ,fractal dimension ,gabapentin ,gadolinium (III)-based composites ,gradient broadening ,green metallic luster ,heterogeneous catalysis sugar conversion ,heteronuclei ,hydrogel ,hydrophilic matrix tablets ,hyperpolarization ,identification ,impurity A ,induction period ,lamellar 2D zeolites ,lanthanides ,limit of the quantitation ,linearity ,low field NMR ,low-field NMR spectroscopy ,magnetic resonance ,magnetic resonance imaging ,magnetic resonance imaging (MRI) ,magnetic resonance imaging contrast agents ,maltenes ,moisture content (MC) ,mordenite ,nanodots ,natural soil material ,non-deuterated solvent ,nuclear magnetic resonance imaging ,paramagnetic relaxation enhancement ,partially saturated ,pillared zeolites ,pipe flow ,plasticizer ,polymerization reaction ,polyoxometalates ,pore evolution ,porous material ,precision ,profile ,qNMR ,quantification ,relaxation ,relaxation times ,relaxivity ,relaxometry ,renal clearance ,repeatability ,reptation ,robustness ,silane ,siloxane ,solid-state NMR spectroscopy ,solution-state NMR ,specificity ,swelling ,time-domain NMR ,titanium dioxide TiO2 ,two-phase flow ,ultrasonic ,validation ,velocity mapping ,water content ,water flow ,waterlogged wood ,wood ,wood conservation ,wood consolidation ,zeolites - Abstract
Summary: The development of science has led to the emergence of many new modern materials, which also require more advanced tools for their characterization and analysis. NMR and MRI are certainly among such tools, also due to their continuous development, which has made them more powerful, versatile, and sensitive. With these advances, these two techniques have been able to address many open problems associated with the emergence of new materials.This reprint comprises a collection of advanced NMR and MRI techniques and methods, together with a demonstration of their application to the target materials for which they were designed and optimized. These are presented in 25 original, peer-reviewed articles for the Special Issue in the MDPI journal Molecules. The topics covered include MR methods in pharmaceutical research, NMR in cement research, MR methods in wood research, diffusion in materials, characterization of materials by NMR relaxometry, NMR spectroscopy of materials, and MRI of materials.
12. Motion-sensitized SPRITE measurements of hydrodynamic cavitation in fast pipe flow.
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Adair, Alexander, Mastikhin, Igor V., and Newling, Benedict
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MAGNETIC resonance angiography , *CAVITATION , *PIPE flow , *MAGNETIC resonance imaging , *PHASE coding - Abstract
The pressure variations experienced by a liquid flowing through a pipe constriction can, in some cases, result in the formation of a bubble cloud (i.e., hydrodynamic cavitation). Due to the nature of the bubble cloud, it is ideally measured through the use of non-optical and non-invasive techniques; therefore, it is well-suited for study by magnetic resonance imaging. This paper demonstrates the use of Conical SPRITE (a 3D, centric-scan, pure phase-encoding pulse sequence) to acquire time-averaged void fraction and velocity information about hydrodynamic cavitation for water flowing through a pipe constriction. [ABSTRACT FROM AUTHOR]
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- 2018
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13. Visualization of CSF Flow with Time-resolved 3D MR Velocity Mapping in Aqueductal Stenosis Before and After Endoscopic Third Ventriculostomy.
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Brandner, Sebastian, Buchfelder, Michael, Eyuepoglu, Ilker Y., Luecking, Hannes, Doerfler, Arnd, and Stadlbauer, Andreas
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Purpose: The aim of this study was to evaluate timed-resolved three-dimensional (3D) magnetic resonance (MR) velocity mapping as a method for investigation of cerebrospinal fluid (CSF) flow changes in patients with aqueductal stenosis (AS) treated by endoscopic third ventriculostomy (ETV).Methods: The MR velocity mapping was performed in 12 AS patients before and after ETV and in 10 healthy volunteers by using a 3-Tesla MR system. Time-resolved 3D MR velocity mapping data were acquired with a standard 3D phase contrast (PC) sequence with cardiac triggering. Values of mean (v
mean ) and maximum (vpeak ) velocity were measured at several ventricular structures using dedicated software.Results: Of the patients 11 showed a satisfactory clinical improvement after ETV, whereas one patient needed subsequent shunt implantation. All AS patients showed significant hypomotile CSF flow dynamics in the third ventricle when compared to healthy subjects before surgery (p < 0.05). In contrast, CSF flow velocity was increased within the Foramen of Monro in AS patients. After ETV, all AS patients showed a decrease of CSF flow dynamics within the third ventricle. Mean and peak CSF flow velocities through the ventriculostomy were 1.72 ± 0.59 cm/s (vmean ) and 3.53 ± 0.79 cm/s (vpeak ), respectively after ETV. The patient who needed shunt implantation after ETV had the lowest flow velocities through the ventriculostomy.Conclusion: This study demonstrates that timed-resolved 3D MR velocity mapping is a useful imaging investigation for diagnostics and follow-up in patients with AS. This new technique provides an insight into the physiological CSF flow changes related with AS and its treatment. [ABSTRACT FROM AUTHOR]- Published
- 2018
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14. Rectification of Image Velocity Results (RIVeR): A simple and user-friendly toolbox for large scale water surface Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV).
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Patalano, Antoine, García, Carlos Marcelo, and Rodríguez, Andrés
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PARTICLE image velocimetry , *PARTICLE tracking velocimetry , *LARGE scale integration of circuits , *COMPUTERS in geology , *HYDRAULIC models - Abstract
LSPIV (Large Scale Particle Image Velocimetry) and LSPTV (Large Scale Particle Tracking Velocimetry) are used as relatively low-cost and non-intrusive techniques for water-surface velocity analysis and flow discharge measurements in rivers or large-scale hydraulic models. This paper describes a methodology based on state-of-the-art tools (for example, that apply classical PIV/PTV analysis) resulting in large-scale surface-flow characterization according to the first operational version of the RIVeR (Rectification of Image Velocity Results). RIVeR is developed in Matlab and is designed to be user-friendly. RIVeR processes large-scale water-surface characterization such as velocity fields or individual trajectories of floating tracers. This work describes the wide range of application of the techniques for comparing measured surface flows in hydraulic physical models to flow discharge estimates for a wide range of flow events in rivers (for example, low and high flows). [ABSTRACT FROM AUTHOR]
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- 2017
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15. Image-based background phase error correction in 4D flow MRI revisited.
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Busch, Julia, Giese, Daniel, and Kozerke, Sebastian
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ALGORITHMS ,AORTA ,DIAGNOSTIC imaging ,DIGITAL image processing ,MAGNETIC resonance imaging ,COMPUTERS in medicine ,IMAGING phantoms ,RESEARCH evaluation ,THREE-dimensional imaging ,HUMAN research subjects ,STATISTICAL models - Abstract
Purpose: To correct background phase errors in phase-contrast magnetic resonance imaging (MRI), image-based correction by referencing through stationary tissue is widely used. The aim of the present study was a detailed assessment of background phase errors in 4D Flow MRI and limitations of image-based correction.Materials and Methods: In a phantom study, 4D Flow MRI data were acquired for typical settings on two clinical 3T MR systems. Background errors were analyzed with respect to their spatial order and minimum requirements regarding the signal-to-noise ratio (SNR) and the amount of stationary tissue for image-based correction were assessed. For in vivo evaluation, data of the aorta were acquired on one 3T MR system in five healthy subjects including subsequent scans on the stationary phantom as reference.Results: Background errors were found to exhibit spatial variation of first- to third-order. For correction, a minimum SNR of 20 was needed to achieve an error of less than 0.4% of the encoding velocity. The minimum amount of stationary tissue was strongly dependent on the spatial order requiring at least 25%, 60%, and 75% of stationary tissue for first-, second-, and third-order correction. In vivo evaluation showed that with 35-41% of stationary tissue available only first-order correction yielded a significant reduction (P < 0.01).Conclusion: Background phase errors can range from first to third spatial order in 4D Flow MRI requiring correction with appropriate polynomials. At the same time, the limited amount of stationary tissue available in vivo limits image-based background phase correction to first spatial order.Level Of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1516-1525. [ABSTRACT FROM AUTHOR]- Published
- 2017
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16. ICE FLOW VELOCITY MAPPING IN EAST ANTARCTICA USING HISTORICAL IMAGES FROM 1960s TO 1980s: RECENT PROGRESS
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S. Luo, Y. Cheng, Z. Li, Y. Wang, K. Wang, X. Wang, G. Qiao, W. Ye, Y. Li, M. Xia, X. Yuan, Y. Tian, X. Tong, and R. Li
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Technology ,Series (stratigraphy) ,Outcrop ,Ice stream ,Elevation ,Antarctic ice sheet ,Context (language use) ,East antarctica ,Engineering (General). Civil engineering (General) ,TA1501-1820 ,Velocity mapping ,Climatology ,Applied optics. Photonics ,TA1-2040 ,Geology - Abstract
Recent research indicates that the estimated elevation changes and associated mass balance in East Antarctica are of some degree of uncertainty; a light accumulation has occurred in its vast inland regions, while mass loss in Wilkes Land appears significant. It is necessary to study the mass change trend in the context of a long period of the East Antarctic Ice Sheet (EAIS). The input-output method based on surface ice flow velocity and ice thickness is one of the most important ways to estimate the mass balance, which can provide longer-term knowledge of mass balance because of the availability of the early satellites in 1960s. In this study, we briefly describe the method of extracting ice velocity based on the historical optical images from 1960s to 1980s. Based on the draft ice velocity map of the EAIS using this method, we conduct a series of validation experiments, including comparisons with in-situ measurement, existing historical maps and rock outcrop dataset. Finally, we use the input-output method to estimate mass balance in some regions of EAIS using the generated velocity map.
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- 2021
17. Predictive K-PLSR Myocardial Contractility Modeling with Phase Contrast MR Velocity Mapping
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Lee, Su-Lin, Wu, Qian, Huntbatch, Andrew, Yang, Guang-Zhong, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Ayache, Nicholas, editor, Ourselin, Sébastien, editor, and Maeder, Anthony, editor
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- 2007
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18. Ultrasound velocity mapping to evaluate gluing quality in CLT panels from plantation wood species
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Roger Moya, Freddy Muñoz, and Carolina Tenorio
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Materials science ,Velocity mapping ,business.industry ,Delamination ,Ultrasound ,General Materials Science ,Forestry ,Plant Science ,Composite material ,Glue line ,business ,Industrial and Manufacturing Engineering - Abstract
Evaluation of the glue line in CLT panels and in other wood composite products in general is of great interest. Non-destructive methods such as determination of the velocity of ultrasound waves going through the materials are commonly applied to evaluate wood products. The present work is aimed at mapping ultrasound velocity (UV) to identify problems of glue line delamination in CLT panels of 3 and 5 layers made from Gmelina arborea and Tectona grandis timber. The results showed higher UV in the 3-layered panels in both timber species, and low UV and the presence of regions of low velocity in UV isocurves of the 5-layered CLT panels, due to separation of glue line, such as un-gluing and delamination. A UV reference value for glue line free of delamination problems of 927 and 1039 m/s was set for CLT panels of G. arborea of 3 and 5 layers, respectively, and of 1073 and 946 m/s for CLT panels of T. grandis of 3 and 5 layers, respectively. Values below the UV reference suggest the presence of some anomalies or problems of delamination, such as gluing defects.
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- 2021
19. Ion Imaging Studies of Chemical Dynamics
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Chandler, D. W., Barker, J. R., Heck, A. J. R., Janssen, M. H. M., Lorenz, K. T., Neyer, D. W., Roeterdink, W., Stolte, S., Yoder, L. M., and Campargue, Roger, editor
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- 2001
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20. Selective arterial spin labeling in conjunction with phase-contrast acquisition for the simultaneous visualization of morphology, flow direction, and velocity of individual arteries in the cerebrovascular system.
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Lindner, Thomas, Larsen, Naomi, Jansen, Olav, and Helle, Michael
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Purpose In various cerebrovascular diseases the visualization of individual arteries and knowledge about their hemodynamic properties, like flow velocity and direction, can become important for an accurate diagnosis. Magnetic resonance angiography methods are intended to acquire this information, but often a single acquisition is not sufficient to retrieve all of this desired information. Methods Using selective arterial spin labeling (ASL) methods, a single artery of interest can be tagged and visualized, whereas quantitative information about hemodynamics can be retrieved using phase-contrast techniques that are often limited regarding their selectivity. In this study, a method that allows for velocity mapping of individual arteries by incorporating phase-contrast preparation into selective ASL angiography measurements is presented. Several postprocessing steps are required to generate velocity and directional-encoded maps of selected arteries from the data acquired in a single scan. Results The method was successfully evaluated in healthy volunteers, and a first application in two selected patients is presented. In one patient, an aneurysm of the middle cerebral artery is investigated, and in the second patient it is used to visualize an arterio-venous malformation. Conclusion Selective ASL imaging in conjunction with phase-contrast acquisition allows for investigating hemodynamic properties of individual arteries. Magn Reson Med 78:1469-1475, 2017. © 2016 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]
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- 2017
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21. ESTIMATION OF WALL SHEAR STRESS USING 4D FLOW CARDIOVASCULAR MRI AND COMPUTATIONAL FLUID DYNAMICS.
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SOUDAH, E., CASACUBERTA, J., GAMEZ-MONTERO, P. J., PÉREZ, J. S., RODRÍGUEZ-CANCIO, M., RAUSH, G., LI, C. H., CARRERAS, F., and CASTILLA, R.
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ARTERIAL diseases , *SHEARING force , *BLOOD flow , *CARDIOVASCULAR system , *THREE-dimensional imaging , *ESTIMATION theory , *DIAGNOSIS , *MAGNETIC resonance imaging - Abstract
In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the WSS plays a significant role, together with hemodynamic indicators, in initiation and progression of the vascular diseases. Estimation of WSS values, therefore, may be of clinical significance and the methods employed for its measurement are crucial for clinical community. Recently, four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been widely used in a number of applications for visualization and quantification of blood flow, and although the sensitivity to blood flow measurement has increased, it is not yet able to provide an accurate three-dimensional (3D) WSS distribution. The aim of this work is to evaluate the aortic blood flow features and the associated WSS by the combination of 4D flow cardiovascular magnetic resonance (4D CMR) and computational fluid dynamics technique. In particular, in this work, we used the 4D CMR to obtain the spatial domain and the boundary conditions needed to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. Similar WSS distributions were found for cases simulated. A sensitivity analysis was done to check the accuracy of the method. 4D CMR begins to be a reliable tool to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. The combination of both techniques may provide the ideal tool to help tackle these and other problems related to wall shear estimation. [ABSTRACT FROM AUTHOR]
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- 2017
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22. Photodissociation dynamics of AlO at 193 nm using time-sliced ion velocity imaging
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Yu-jie Ma, Fang-fang Li, Jia-xing Liu, Fengyan Wang, and Guanjun Wang
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Materials science ,Photodissociation ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Dissociation (chemistry) ,0104 chemical sciences ,Ion ,Ion dissociation ,chemistry ,Velocity mapping ,Aluminium ,Ionization ,Physics::Atomic and Molecular Clusters ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,0210 nano-technology ,Anisotropy - Abstract
The photodissociation dynamics of AlO at 193 nm is studied using time-sliced ion velocity mapping. Two dissociation channels are found through the speed and angular distributions of aluminum ions: one is one-photon dissociation of the neutral AlO to generate Al(2Pu)+O(3Pg), and the other is two-photon ionization and then dissociation of AlO+ to generate Al+(1Sg)+O(3Pg). Each dissociation channel includes the contribution of AlO in the vibrational states v=0-2. The anisotropy parameter of the neutral dissociation channel is more dependent on the vibration state of AlO than the ion dissociation channel.
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- 2020
23. Magnetic Resonance Imaging of Cardiac Function and Flow: Present and Future
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van Rossum, Albert C., Van Der Wall, Ernst E., editor, Blanksma, Paul K., editor, Niemeyer, Menco G., editor, Vaalburg, Willem, editor, and Crijns, Harry J. G. M., editor
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- 1998
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24. Data fusion by radial basis function approximation with application in varying velocity mapping
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Huazhong Wang, Shouwei Liu, and Ting Lei
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Computer science ,Velocity mapping ,Mathematical analysis ,Radial basis function ,Sensor fusion - Published
- 2021
25. Magnetic Resonance Imaging measurements of a water spray upstream and downstream of a spray nozzle exit orifice.
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Mastikhin, Igor, Arbabi, Aidin, and Bade, Kyle M.
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MAGNETIC resonance imaging , *SPRAY nozzles , *ORIFICE plates (Fluid dynamics) , *PARTICLE dynamics analysis , *X-rays , *FLUID flow - Abstract
Sprays are dynamic collections of droplets dispersed in a gas, with many industrial and agricultural applications. Quantitative characterization is essential for understanding processes of spray formation and dynamics. There exists a wide range of measurement techniques to characterize sprays, from direct imaging to phase Doppler interferometry to X-rays, which provide detailed information on spray characteristics in the “far-nozzle” region (≫10 diameters of the nozzle). However, traditional methods are limited in their ability to characterize the “near-nozzle” region where the fluid may be inside the nozzle, optically dense, or incompletely atomized. Magnetic Resonance Imaging (MRI) presents potential as a non-invasive technique that is capable of measuring optically inaccessible fluid in a quantitative fashion. In this work, MRI measurements of the spray generated by ceramic flat-fan nozzles were performed. A wide range of flow speeds in the system (0.2 to >25 m/s) necessitated short encoding times. A 3D Conical SPRITE and motion-sensitized 3D Conical SPRITE were employed. The signal from water inside the nozzle was well-characterized, both via proton density and velocity measurements. The signal outside the nozzle, in the near-nozzle region, was detectable, corresponding to the expected flat-fan spray pattern up to 3 mm away. The results demonstrate the potential of MRI for measuring spray characteristics in areas inaccessible by other methods. [ABSTRACT FROM AUTHOR]
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- 2016
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26. Magnetic resonance imaging of the cardiovascular system
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Underwood, Richard, Reiber, Johan H. C., editor, and Van Der Wall, Ernst E., editor
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- 1992
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27. Magnetic resonance imaging and quantitation of blood flow
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van Rossum, Albert C., Sprenger, Michiel, van der Wall, Ernst E., editor, and de Roos, Albert, editor
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- 1991
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28. Manipulator control in singular configurations—Motion in degenerate directions
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Egeland, Olav, Spangelo, Inge, Thoma, M., editor, Wyner, A., editor, and Canudas de Wit, Carlos, editor
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- 1991
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29. Quantitative In Vivo Blood Flow Measurements with Magnetic Resonance Imaging
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Maier, S. E., Boesiger, P., Lanzer, Peter, editor, and Yoganathan, Ajit P., editor
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- 1991
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30. ICE FLOW VELOCITY MAPPING OF EAST ANTARCTICA FROM 1963 TO 1989
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Y. Cheng, X. Li, G. Qiao, W. Ye, Y. Huang, Y. Li, K. Wang, Y. Tian, X. Tong, and R. Li
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lcsh:Applied optics. Photonics ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,lcsh:T ,Ice stream ,0211 other engineering and technologies ,lcsh:TA1501-1820 ,Antarctic ice sheet ,Glacier ,East antarctica ,02 engineering and technology ,Surface velocity ,lcsh:Technology ,01 natural sciences ,lcsh:TA1-2040 ,Velocity mapping ,Physical geography ,lcsh:Engineering (General). Civil engineering (General) ,Scale (map) ,Geology ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences - Abstract
Long-time serial observation of surface ice flow velocity in Antarctic is a crucial component in estimating the mass balance of Antarctic ice sheet. However, there is a lack of historical continental scale velocity maps of Antarctica before the 1990s. Historical optical images such as ARGON and Landsat images before 1990s are difficult to be used for ice flow velocity mapping, due to the fact that they are mostly not strictly geo-processed (e.g., ortho-rectified) and the image quality is lower than those of recent sensors. This paper presents a systematic framework for developing a surface velocity map of East Antarctica from 1963 to 1989 based on historical ARGON and Landsat images, followed by analysis of spatial-temporal changes of the ice flow velocity in some major glaciers, as well as the dynamic changes. The preliminary comparison with existing products suggests that the glaciers in Wilkes Land experienced an increasing trend with obvious fluctuations during the past ∼50 years, while the glaciers near Transantarctic Mountains tended to be stable or slightly fluctuating to a certain degree.
- Published
- 2019
31. 4-Dimensional Velocity Mapping Cardiac Magnetic Resonance of Extracardiac Bypass for Aortic Coarctation Repair
- Author
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Chrysanthos Grigoratos, N Martini, Pierluigi Festa, Daniele Della Latta, Lamia Ait Ali, and Dante Chiappino
- Subjects
medicine.medical_specialty ,4D flow CMR ,business.industry ,Case Report ,macromolecular substances ,cardiac magnetic resonance ,3D imaging ,Clinical Case ,Velocity mapping ,RC666-701 ,Internal medicine ,Descending aorta ,medicine.artery ,cardiovascular system ,Cardiology ,Diseases of the circulatory (Cardiovascular) system ,Medicine ,cardiovascular diseases ,Cardiology and Cardiovascular Medicine ,business ,Cardiac magnetic resonance ,aortic coarctation - Abstract
This report describes a case of a young lady who, following extracardiac bypass between ascending and descending aorta for severe aortic coarctation,…, This report describes a case of a young lady who, following extracardiac bypass between ascending and descending aorta for severe aortic coarctation, underwent 4-dimensional flow cardiac magnetic resonance, a technique that, by 3-dimensional flow assessment over time (4-dimensional), allows not only quantification of flows but also wall shear stress. In this case, increased wall shear stress was observed in the conduit's acute angle (kinking) as well as at the distal anastomosis level. The authors postulate that increased wall shear stress could help identify and risk stratify adult congenital heart disease who could develop vascular complications in the future. (Level of Difficulty: Intermediate.), Graphical abstract
- Published
- 2019
32. Radial k-t SPIRiT: Autocalibrated parallel imaging for generalized phase-contrast MRI.
- Author
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Santelli, Claudio, Schaeffter, Tobias, and Kozerke, Sebastian
- Abstract
Purpose To extend SPIRiT to additionally exploit temporal correlations for highly accelerated generalized phase-contrast MRI and to compare the performance of the proposed radial k-t SPIRiT method relative to frame-by-frame SPIRiT and radial k-t GRAPPA reconstruction for velocity and turbulence mapping in the aortic arch. Theory and Methods Free-breathing navigator-gated two-dimensional radial cine imaging with three-directional multi-point velocity encoding was implemented and fully sampled data were obtained in the aortic arch of healthy volunteers. Velocities were encoded with three different first gradient moments per axis to permit quantification of mean velocity and turbulent kinetic energy. Velocity and turbulent kinetic energy maps from up to 14-fold undersampled data were compared for k-t SPIRiT, frame-by-frame SPIRiT, and k-t GRAPPA relative to the fully sampled reference. Results Using k-t SPIRiT, improvements in magnitude and velocity reconstruction accuracy were found. Temporally resolved magnitude profiles revealed a reduction in spatial blurring with k-t SPIRiT compared with frame-by-frame SPIRiT and k-t GRAPPA for all velocity encodings, leading to improved estimates of turbulent kinetic energy. Conclusion k-t SPIRiT offers improved reconstruction accuracy at high radial undersampling factors and hence facilitates the use of generalized phase-contrast MRI for routine use. Magn Reson Med 72:1233-1245, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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33. MACROPORE VELOCITY MAPPING OF ALLUVIAL SOIL USING TEMPORAL ELECTRICAL RESISTIVITY IMAGING
- Author
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Bharat Sharma Acharya, John P. Hager, Todd Halihan, Lucie Guertault, and Garey A. Fox
- Subjects
Macropore ,Velocity mapping ,Soil science ,Alluvium ,Electrical resistivity tomography ,Geology - Published
- 2021
34. Fluid dynamics of aortic root dilation in Marfan syndrome.
- Author
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Querzoli, Giorgio, Fortini, Stefania, Espa, Stefania, Costantini, Martina, and Sorgini, Francesca
- Subjects
- *
FLUID dynamics , *MARFAN syndrome , *DISSECTION , *AORTA surgery , *GENETIC disorders ,DIAGNOSIS of aortic diseases - Abstract
Aortic root dilation and propensity to dissection are typical manifestations of the Marfan Syndrome (MS), a genetic defect leading to the degeneration of the elastic fibres. Dilation affects the structure of the flow and, in turn, altered flow may play a role in vessel dilation, generation of aneurysms, and dissection. The aim of the present work is the investigation in-vitro of the fluid dynamic modifications occurring as a consequence of the morphological changes typically induced in the aortic root by MS. A mock-loop reproducing the left ventricle outflow tract and the aortic root was used to measure time resolved velocity maps on a longitudinal symmetry plane of the aortic root. Two dilated model aortas, designed to resemble morphological characteristics typically observed in MS patients, have been compared to a reference, healthy geometry. The aortic model was designed to quantitatively reproduce the change of aortic distensibility caused by MS. Results demonstrate that vorticity released from the valve leaflets, and possibly accumulating in the root, plays a fundamental role in redirecting the systolic jet issued from the aortic valve. The altered systolic flow also determines a different residual flow during the diastole. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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35. Accelerated radial Fourier-velocity encoding using compressed sensing.
- Author
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Hilbert, Fabian, Wech, Tobias, Hahn, Dietbert, and Köstler, Herbert
- Abstract
Copyright of Zeitschrift für Medizinische Physik is the property of Elsevier GmbH, Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2014
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36. Effect of temporal resolution on 4D flow MRI in the portal circulation.
- Author
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Landgraf, Benjamin R., Johnson, Kevin M., Roldán‐Alzate, Alejandro, Francois, Christopher J., Wieben, Oliver, and Reeder, Scott B.
- Abstract
Purpose To demonstrate the use of temporal averaging with radial 4D flow magnetic resonance imaging (MRI) to reduce scan time for quantification and visualization of flow in the portal circulation. This study compared phase-contrast MR angiography, 3D flow visualization, and flow quantification of portal venous hemodynamics of time-averaged vs. time-resolved reconstructions. Materials and Methods Time-resolved 3D radial ('4D') phase contrast data were acquired from 44 subjects (15 volunteers, 29 cirrhosis patients) at 3T. Images were reconstructed as a fully sampled time-resolved reconstruction and multiple time-averaged reconstructions using a variable number of acquired projections to simulate different scan times. Images from each reconstruction were evaluated to compare the quality of anatomical and hemodynamic visualization. Results Time-averaged reconstructions outperformed time-resolved reconstructions for flow quantification (3.9 ± 3.1% error vs. 5.2 ± 4.4% error), average streamline length (47 ± 7 mm vs. 34 ± 15 mm), and visualization quality (average grading = 3.7 ± 0.5 vs. 2.2 ± 0.9). In addition, excellent visualization quality was achieved using fewer acquired projections. Conclusion Reductions in scan time can be achieved through time-averaging while still providing excellent visualization and quantification in the portal circulation. Scan time reduction of up to 70%-80% was possible for high-quality assessment, translating into a reduction in scan time from 10-12 minutes to ∼3-4 minutes. J. Magn. Reson. Imaging 2014;39:819-826. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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37. Spatially Resolved Velocity Mapping of the Melt Plume During High-Pressure Gas Atomization of Liquid Metals
- Author
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T. D. Bigg and Andrew M. Mullis
- Subjects
Materials science ,Spatially resolved ,0211 other engineering and technologies ,Metals and Alloys ,02 engineering and technology ,Mechanics ,Condensed Matter Physics ,Kinetic energy ,01 natural sciences ,010305 fluids & plasmas ,Plume ,Mechanics of Materials ,Velocity mapping ,0103 physical sciences ,Metallic materials ,Materials Chemistry ,Supersonic speed ,High pressure gas ,021102 mining & metallurgy - Abstract
We present details of an image analysis algorithm designed specifically to determine the velocity of material in the melt plume during high-pressure, close-coupled gas atomization. Following high-speed filming (16,000 fps) pairs of images are used to identify and track dominant features within the plume. Due to the complexity of the atomization plume, relatively few features are tracked between any given pair of images, but by averaging over the many thousands of frames obtained during high-speed filming a spatially resolved map of the average velocity of material in the plume can be built up. Velocities in the plume are typically very low compared to that of the supersonic gas, being around 30 m s−1 on the margins of the plume where the melt interacts strongly with the gas and dropping to −1 in the center of the melt plume. Consequently, the efficiency of the atomizer in transferring kinetic energy from the gas to the melt is correspondingly very low, with this being estimated as being no more than 0.1 pct.
- Published
- 2020
38. Another useful ice velocity mapping tool using images
- Author
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Ted Scambos
- Subjects
Velocity mapping ,Geology ,Remote sensing - Published
- 2020
39. Quantitative Microvessel Analysis with 3-D Super-Resolution Ultrasound and Velocity Mapping
- Author
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Christopher Dunsby, Piero Tortoli, Enrico Boni, Alessandro Ramalli, Meng-Xing Tang, Sevan Harput, Matthieu Toulemonde, and Kirsten Christensen-Jeffries
- Subjects
Physics ,Ground truth ,medicine.diagnostic_test ,business.industry ,Ultrasound ,Magnetic resonance imaging ,01 natural sciences ,Tortuosity ,Superresolution ,030218 nuclear medicine & medical imaging ,Visualization ,03 medical and health sciences ,0302 clinical medicine ,Velocity mapping ,0103 physical sciences ,medicine ,business ,010301 acoustics ,Microvessel ,Biomedical engineering - Abstract
Medical image analysis is becoming increasingly accessible in the clinic. Computed tomography (CT) or magnetic resonance imaging (MRI) scans are usually post-processed to generate a 3-D visualization of the human body for surgical assistance or extract quantitative data to provide additional diagnostic information. Three dimensional super-resolution ultrasound (SR US) imaging can provide similar information at a micro-level without the high cost or ionising radiation. In this study, we implemented a high volumetric-rate 3-D SR US imaging with a 2-D spiral-shaped array and imaged an in vitro microvascular structure. From the 3-D SR US images clinically relevant parameters, such as microvascular flow rate, microvessel density and tortuosity, were extracted and compared with the ground truth.
- Published
- 2020
40. COMPILING TECHNIQUES FOR EAST ANTARCTIC ICE VELOCITY MAPPING BASED ON HISTORICAL OPTICAL IMAGERY
- Author
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X. Li, R. Li, G. Qiao, Y. Cheng, W. Ye, T. Gao, Y. Huang, Y. Tian, and X. Tong
- Subjects
lcsh:Applied optics. Photonics ,010504 meteorology & atmospheric sciences ,lcsh:T ,Ice stream ,0211 other engineering and technologies ,Antarctic ice sheet ,lcsh:TA1501-1820 ,East antarctica ,02 engineering and technology ,Geodesy ,Surface velocity ,01 natural sciences ,lcsh:Technology ,Sea level rise ,Velocity mapping ,lcsh:TA1-2040 ,Scale (map) ,Parallax ,lcsh:Engineering (General). Civil engineering (General) ,Geology ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences - Abstract
Ice flow velocity over long time series in East Antarctica plays a vital role in estimating and predicting the mass balance of Antarctic Ice Sheet and its contribution to global sea level rise. However, there is no Antarctic ice velocity product with large space scale available showing the East Antarctic ice flow velocity pattern before the 1990s. We proposed three methods including parallax decomposition, grid-based NCC image matching, feature and gird-based image matching with constraints for estimation of surface velocity in East Antarctica based on ARGON KH-5 and LANDSAT imagery, showing the feasibility of using historical optical imagery to obtain Antarctic ice motion. Based on these previous studies, we presented a set of systematic method for developing ice surface velocity product for the entire East Antarctica from the 1960s to the 1980s in this paper.
- Published
- 2018
41. Status and prospects of exploration and exploitation key technologies of the deep petroleum resources in onshore China
- Author
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Yunhua Ge, Chao Ni, Genshun Yao, Xiaodong Fu, Zandong Sun, Chunhao Yu, Jianyong Zhang, Xianyou Yang, Xianzhu Wu, and Long Wen
- Subjects
lcsh:Gas industry ,Petroleum engineering ,Geophysical imaging ,business.industry ,lcsh:TP751-762 ,020209 energy ,Fossil fuel ,Seismic migration ,Drilling ,02 engineering and technology ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry.chemical_compound ,chemistry ,Velocity mapping ,0202 electrical engineering, electronic engineering, information engineering ,Key (cryptography) ,Petroleum ,China ,business ,Geology ,0105 earth and related environmental sciences - Abstract
In recent years, China's deep oil and gas exploration and exploitation have developed rapidly. Technological advancements have played an important role in the rapid exploration and highly efficient development. Aimed at the complex engineering geological environment of deep oil and gas in China, this paper has combined the four technological systems that have made significant progress, mainly including: (1) seismic imaging and reservoir prediction techniques for deep–burial complex structures, includign “2W1S” technique (wide-band, wide azimuth, and small bin), RTM (Reverse Time Migration), integrated modeling technology for complex structures and variable velocity mapping technique, improving structural interpretation accuracy, ensuring high precision ofimaging, and prediction for deep geological bodies; (2) deep speed raising and efficiency drilling technology series, which significantly improved the drilling speed, in turn reduced the drilling cost and drilling risk; (3) development of a deep high-temperature and high-pressure logging technology series, which provided a guarantee for the accurate identification of reservoir properties and fluid properties; (4) the efficient development technology for deep reservoirs, especially the development and maturity of the reconstruction volume technology, improve the production of single well and the benefit of deep oil and gas development. This paper further points out the improvement direction of the four major technology series of deep oil based on the analysis of the current development of the four major technological systems. Moreover, the development of applicability and economy for technical system is the key to realize high efficiency and low-cost exploration and development of deep oil and gas. Keywords: Deep oil & gas, Exploration and exploitation technologies, Seismic, Logging, Drilling, Petroleum reservoir stimulation
- Published
- 2018
42. Rectification of Image Velocity Results (RIVeR): A simple and user-friendly toolbox for large scale water surface Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV)
- Author
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Carlos M. García, Andrés Rodriguez, and Antoine Patalano
- Subjects
Scale (ratio) ,0208 environmental biotechnology ,Flow (psychology) ,INGENIERÍAS Y TECNOLOGÍAS ,02 engineering and technology ,Lsptv ,Stream Gauging ,Particle tracking velocimetry ,Range (statistics) ,Computer vision ,Computers in Earth Sciences ,MATLAB ,Remote sensing ,computer.programming_language ,Physical model ,business.industry ,Velocity Mapping ,Velocimetry ,020801 environmental engineering ,Ingeniería Civil ,Particle image velocimetry ,Surface-Flow Measurement ,Artificial intelligence ,business ,Otras Ingeniería Civil ,computer ,Lspiv ,Geology ,Information Systems - Abstract
LSPIV (Large Scale Particle Image Velocimetry) and LSPTV (Large Scale Particle Tracking Velocimetry) are used as relatively low-cost and non-intrusive techniques for water-surface velocity analysis and flow discharge measurements in rivers or large-scale hydraulic models. This paper describes a methodology based on state-of-the-art tools (for example, that apply classical PIV/PTV analysis) resulting in large-scale surface-flow characterization according to the first operational version of the RIVeR (Rectification of Image Velocity Results). RIVeR is developed in Matlab and is designed to be user-friendly. RIVeR processes large-scale water-surface characterization such as velocity fields or individual trajectories of floating tracers. This work describes the wide range of application of the techniques for comparing measured surface flows in hydraulic physical models to flow discharge estimates for a wide range of flow events in rivers (for example, low and high flows). Fil: Patalano, Antoine. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina Fil: Garcia Rodriguez, Carlos Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina Fil: Rodriguez, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentina
- Published
- 2017
43. Aortic wall shear stress in Marfan syndrome.
- Author
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Geiger, Julia, Arnold, Raoul, Herzer, Lena, Hirtler, Daniel, Stankovic, Zoran, Russe, Max, Langer, Mathias, and Markl, Michael
- Abstract
The aim of this study was to quantify changes in thoracic aortic wall shear stress (WSS) in asymptomatic patients with Marfan syndrome (MFS) compared with healthy controls. WSS in the thoracic aorta was quantified based on time-resolved 3D phase contrast MRI with three-directional velocity encoding (4D flow MRI, temporal resolution ∼44 ms, spatial resolution ∼2.5 mm) in 24 patients with confirmed MFS (age = 18 ± 12 years) and in 12 older healthy volunteers (age = 25 ± 3 years). Diameters of the thoracic aorta normalized to body surface area were similar for both groups. Peak systolic velocity, absolute WSS, time-averaged WSS, circumferential WSS, peak systolic WSS, and WSS eccentricity were calculated in eight analysis planes distributed along the thoracic aorta. Plane-wise comparison revealed significant differences between MFS patients and volunteers in the proximal ascending aorta for peak systolic velocities (1.11 ± 0.23 m/s vs. 1.34 ± 0.18 m/s, P = 0.004) and circumferential WSS (0.14 ± 0.03 N/m
2 vs. 0.11 ± 0.02 N/m2 , P = 0.007). WSS eccentricity was altered in most of the ascending aorta and proximal arch ( P = 0.009-0.020). MFS patients demonstrated segmental differences in peak systolic WSS with a significantly higher WSS at the inner curvature in the proximal ascending aorta and at the anterior part in the more distal ascending aorta ( P < 0.01). These findings indicate differences in WSS associated with MFS despite similar aortic dimensions compared to controls. Magn Reson Med, 70:1137-1144, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]- Published
- 2013
- Full Text
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44. Bayesian multipoint velocity encoding for concurrent flow and turbulence mapping.
- Author
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Binter, Christian, Knobloch, VerENa, Manka, Robert, Sigfridsson, Andreas, and Kozerke, Sebastian
- Abstract
An approach to efficiently measure three-dimensional velocity vector fields and turbulent kinetic energy of blood flow is presented. Multipoint phase-contrast imaging is used in combination with Bayesian analysis to map both mean and fluctuating velocities over a large dynamic range and for practically relevant signal-to-noise ratios. It is demonstrated that the approach permits significant spatiotemporal undersampling to allow for clinically acceptable scan times. Using numerical simulations and in vitro measurements in aortic valve phantoms, it is shown that for given scan time, Bayesian multipoint velocity encoding provides consistently lower errors of velocity and turbulent kinetic energy over a larger dynamic range relative to previous methods. In vitro, significant differences in both peak velocity and turbulent kinetic energy between the aortic CoreValve (150 cm/s, 293 J/m
3 ) and the St. Jude Medical mechanical valve (120 cm/s, 149 J/m3 ) were found. Comparison of peak turbulent kinetic energy measured in a patient with aortic stenosis (950 J/m3 ) and in a patient with an implanted aortic CoreValve (540 J/m3 ) revealed considerable differences relative to the values detected in healthy subjects (149 ± 12 J/m3 ) indicating the potential of the method to provide a comprehensive hemodynamic assessment of valve performance in vivo. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]- Published
- 2013
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45. Orientation Effect in the Low-Energy Electron Attachment to the Apolar Carbon Tetrafluoride Molecule.
- Author
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Xia, Lei, Zeng, Xian‐Jin, Li, Hong‐Kai, Wu, Bin, and Tian, Shan Xi
- Abstract
Electron capture at the carbon–fluorine σ* antibonding orbital accounts for the vector correlations between fragments F− and CF3 or F and CF3− in two complementary dissociation pathways after electron attachment to CF4. An orientation effect in the low‐energy electron attachment is observed by velocity mapping (see picture; C black, F blue). [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
46. Variable velocity encoding in a three-dimensional, three-directional phase contrast sequence: Evaluation in phantom and volunteers.
- Author
-
Nilsson, Anders, Bloch, Karin Markenroth, Carlsson, Marcus, Heiberg, Einar, and Ståhlberg, Freddy
- Abstract
Purpose: To evaluate accuracy and noise properties of a novel time-resolved, three-dimensional, three-directional phase contrast sequence with variable velocity encoding (denoted 4D-vPC) on a 3 Tesla MR system, and to investigate potential benefits and limitations of variable velocity encoding with respect to depicting blood flow patterns. Materials and Methods: A 4D PC-MRI sequence was modified to allow variable velocity encoding (VENC) over the cardiac cycle in all three velocity directions independently. 4D-PC sequences with constant and variable VENC were compared in a rotating phantom with respect to measured velocities and noise levels. Additionally, comparison of flow patterns in the ascending aorta was performed in six healthy volunteers. Results: Phantom measurements showed a linear relationship between velocity noise and velocity encoding. 4D-vPC MRI presented lower noise levels than 4D-PC both in phantom and in volunteer measurements, in agreement with theory. Volunteer comparisons revealed more consistent and detailed flow patterns in early diastole for the variable VENC sequences. Conclusion: Variable velocity encoding offers reduced noise levels compared with sequences with constant velocity encoding by optimizing the velocity-to-noise ratio (VNR) to the hemodynamic properties of the imaged area. Increased VNR ratios could be beneficial for blood flow visualizations of pathology in the cardiac cycle. J. Magn. Reson. Imaging 2012; 36:1450-1459. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
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47. Multipoint 5D flow cardiovascular magnetic resonance - accelerated cardiac- and respiratory-motion resolved mapping of mean and turbulent velocities
- Author
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Walheim, Jonas, Dillinger, Hannes, and Kozerke, Sebastian
- Published
- 2019
- Full Text
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48. Velocity field measurements in sedimentary rock cores by magnetization prepared 3D SPRITE
- Author
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Romanenko, Konstantin, Xiao, Dan, and Balcom, Bruce J.
- Subjects
- *
MAGNETIZATION , *MAGNETIC resonance imaging , *SEDIMENTARY rocks , *MAGNETIC permeability , *POROSITY , *HEWITT-Nachbin spaces - Abstract
Abstract: A time-efficient MRI method suitable for quantitative mapping of 3-D velocity fields in sedimentary rock cores, and granular samples is discussed. The method combines the 13-interval Alternating-Pulsed-Gradient Stimulated-Echo (APGSTE) scheme and three-dimensional Single Point Ramped Imaging with T 1 Enhancement (SPRITE). Collecting a few samples near the q-space origin and employing restricted k-space sampling dramatically improves the performance of the imaging method. The APGSTE–SPRITE method is illustrated through mapping of 3-D velocity field in a macroscopic bead pack and heterogeneous sandstone and limestone core plugs. The observed flow patterns are consistent with a general trend for permeability to increase with the porosity. Domains of low permeability obstruct the flow within the core volume. Water tends to flow along macroscopic zones of higher porosity and across zones of lower porosity. [Copyright &y& Elsevier]
- Published
- 2012
- Full Text
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49. Four-dimensional phase contrast MRI With accelerated dual velocity encoding.
- Author
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Nett, Elizabeth J., Johnson, Kevin M., Frydrychowicz, Alex, Del Rio, Alejandro Munoz, Schrauben, Eric, Francois, Christopher J., and Wieben, Oliver
- Abstract
Purpose: To validate a novel approach for accelerated four-dimensional phase contrast MR imaging (4D PC-MRI) with an extended range of velocity sensitivity. Materials and Methods: 4D PC-MRI data were acquired with a radially undersampled trajectory (PC-VIPR). A dual V
enc (dVenc ) processing algorithm was implemented to investigate the potential for scan time savings while providing an improved velocity-to-noise ratio. Flow and velocity measurements were compared with a flow pump, conventional 2D PC MR, and single Venc 4D PC-MRI in the chest of 10 volunteers. Results: Phantom measurements showed excellent agreement between accelerated dVenc 4D PC-MRI and the pump flow rate (R2 ≥ 0.97) with a three-fold increase in measured velocity-to-noise ratio (VNR) and a 5% increase in scan time. In volunteers, reasonable agreement was found when combining 100% of data acquired with Venc = 80 cm/s and 25% of the high Venc data, providing the VNR of a 80 cm/s acquisition with a wider velocity range of 160 cm/s at the expense of a 25% longer scan. Conclusion: Accelerated dual Venc 4D PC-MRI was demonstrated in vitro and in vivo. This acquisition scheme is well suited for vascular territories with wide ranges of flow velocities such as congenital heart disease, the hepatic vasculature, and others. J. Magn. Reson. Imaging 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]- Published
- 2012
- Full Text
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50. Cardiovascular magnetic resonance physics for clinicians: part II.
- Author
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Biglands, John D., Radjenovic, Aleksandra, and Ridgway, John P.
- Subjects
- *
MAGNETIC resonance imaging , *CORONARY disease , *ANGIOGRAPHY , *EDEMA , *BODY fluid disorders , *EDUCATION of physicians , *CORONARY arteries , *MYOCARDIUM , *PERFUSION , *PHYSICS , *PULSE (Heart beat) , *RADIONUCLIDE imaging , *WAVE analysis , *CONTRAST media , *MAGNETIC resonance angiography - Abstract
This is the second of two reviews that is intended to cover the essential aspects of cardiovascular magnetic resonance (CMR) physics in a way that is understandable and relevant to clinicians using CMR in their daily practice. Starting with the basic pulse sequences and contrast mechanisms described in part I, it briefly discusses further approaches to accelerate image acquisition. It then continues by showing in detail how the contrast behaviour of black blood fast spin echo and bright blood cine gradient echo techniques can be modified by adding rf preparation pulses to derive anumber of more specialised pulse sequences. The simplest examples described include T2-weighted oedema imaging, fat suppression and myocardial tagging cine pulse sequences. Two further important derivatives of the gradient echo pulse sequence, obtained by adding preparation pulses, are used in combination with the administration of a gadolinium-based contrast agent for myocardial perfusion imaging and the assessment of myocardial tissue viability using a late gadolinium enhancement (LGE) technique. These two imaging techniques are discussed in more detail, outlining the basic principles of each pulse sequence, the practical steps required to achieve the best results in a clinical setting and, in the case of perfusion, explaining some of the factors that influence current approaches toperfusion image analysis. The key principles of contrast-enhanced magnetic resonance angiography (CE-MRA) are also explained in detail, especially focusing on timing of the acquisition following contrast agent bolus administration, and current approaches to achieving time resolved MRA. Alternative MRA techniques that do not require the use of an endogenous contrast agent are summarised, and the specialised pulse sequence used to image the coronary arteries, using respiratory navigator gating, is described in detail. The article concludes by explaining the principle behind phase contrast imaging techniques which create images that represent the phase of the MR signal rather than the magnitude. It is shown how this principle can be used to generate velocity maps by designing gradient waveforms that give rise to a relative phase change that is proportional to velocity. Choice of velocity encoding range and key pitfalls in the use of this technique are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
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