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James F Greenleaf - One of the best experts on this subject based on the ideXlab platform.
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measured Wave Dispersion in tubes excited with acoustic radiation force matches theoretical guided Wave Dispersion
Internaltional Ultrasonics Symposium, 2016Co-Authors: Matthew W Urban, James F Greenleaf, Ali Vaziri Astaneh, Wilkins Aquino, Murthy N GuddatiAbstract:Acoustic radiation force (ARF) has been used to generate shear Waves in many different tissues for the purpose of quantifying material properties of those tissues. This method has also been applied to arteries, but care must be taken in this application because Waves produced in the arterial wall are guided Waves. To obtain accurate measurements of mechanical properties of arteries, guided Wave inversion can be used, where experimental Wave Dispersion is iteratively matched with theoretical Dispersion curves. In this paper we study Wave propagation in three sets of rubber tubes with different mechanical properties, and compare their measured and theoretical Dispersion curves. Three sets of tubes were made with outer diameters of 8 mm and wall thicknesses of 1 mm to mimic an adult carotid artery. A different rubber mixture was used for each set of tubes, VytaFlex 10, VytaFlex20, and ReoFlex 30. Reference samples were also poured for testing with hyper-frequency viscoelastic spectroscopy (HFVS) instrument for measurement of the material complex modulus. Wave propagation measurements were made with a Verasonics system and linear array with water inside and surrounding the tubes. Acoustic radiation force was used to generate the Waves with a 200 µs push at 4.1 MHz and plane Wave imaging at a frame rate of 14.9 kHz was used for measuring the propagating Waves. A two-dimensional Fourier transform method was used to extract the Dispersion curves from the measured particle velocity. Theoretical Dispersion curves for flexural modes with circumferential Wavenumber n = 1, 2, 3 were calculated from the material properties measured with HFVS for comparison with the ultrasound-based results. The measured Dispersion curve matches well with theoretical results. However, the match is not with a single theoretical Dispersion curve, but with different theoretical curves at different frequencies. This new approach of matching with multiple theoretical curves can be used for better understanding of Wave propagation in arterial walls and improved characterization of their mechanical properties.
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measurement of viscoelastic properties of in vivo swine myocardium using lamb Wave Dispersion ultrasound vibrometry lduv
IEEE Transactions on Medical Imaging, 2013Co-Authors: Matthew W Urban, Ivan Z Nenadic, Cristina Pislaru, R R Kinnick, James F GreenleafAbstract:Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb Wave Dispersion ultrasound vibrometry (LDUV) is a shear Wave-based method that uses Wave velocity Dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical Waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of Wave propagation were measured over the 50-400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb Wave model to obtain estimates of the shear elasticity, μ1, and viscosity, μ2 as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb Wave model was also studied using simulated data. We demonstrated that Wave velocity measurements and Lamb Wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle.
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lamb Wave Dispersion ultrasound vibrometry lduv method for quantifying mechanical properties of viscoelastic solids
Physics in Medicine and Biology, 2011Co-Authors: Ivan Z Nenadic, Matthew W Urban, Scott Mitchell, James F GreenleafAbstract:Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of shear Wave Dispersion ultrasound vibrometry (SDUV), a noninvasive ultrasound-based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb Wave Dispersion ultrasound vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb Waves and measure the Dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb Wave model was fitted to the Wave speed Dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb Wave Dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM Dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify the mechanical properties of soft tissues with a plate-like geometry.
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shear Wave Dispersion ultrasonic vibrometry for measuring prostate shear stiffness and viscosity an in vitro pilot study
IEEE Transactions on Biomedical Engineering, 2011Co-Authors: F G Mitri, Matthew W Urban, Mostafa Fatemi, James F GreenleafAbstract:This paper reports shear stiffness and viscosity “virtual biopsy” measurements of the three excised noncancerous human prostates using a new tool known as shear Wave Dispersion ultrasound vibrometry (SDUV) in vitro. Improved methods for prostate guided-biopsy are required to effectively guide needle biopsy to the suspected site. In addition, tissue stiffness measurement helps in identifying a suspected site to perform biopsy because stiffness has been shown to correlate with pathologies, such as cancerous tissue. More importantly, early detection of prostate cancer may guide minimally invasive therapy and eliminate insidious procedures. In this paper, “virtual biopsies” were taken in multiple locations in three excised prostates; SDUV shear elasticity and viscosity measurements were performed at the selected “suspicious” locations within the prostates. SDUV measurements of prostate elasticity and viscosity are generally in agreement with preliminary values previously reported in the literature. It is, however, important to emphasize here that the obtained viscoelastic parameters values are local, and not a mean value for the whole prostate.
Matthew W Urban - One of the best experts on this subject based on the ideXlab platform.
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measured Wave Dispersion in tubes excited with acoustic radiation force matches theoretical guided Wave Dispersion
Internaltional Ultrasonics Symposium, 2016Co-Authors: Matthew W Urban, James F Greenleaf, Ali Vaziri Astaneh, Wilkins Aquino, Murthy N GuddatiAbstract:Acoustic radiation force (ARF) has been used to generate shear Waves in many different tissues for the purpose of quantifying material properties of those tissues. This method has also been applied to arteries, but care must be taken in this application because Waves produced in the arterial wall are guided Waves. To obtain accurate measurements of mechanical properties of arteries, guided Wave inversion can be used, where experimental Wave Dispersion is iteratively matched with theoretical Dispersion curves. In this paper we study Wave propagation in three sets of rubber tubes with different mechanical properties, and compare their measured and theoretical Dispersion curves. Three sets of tubes were made with outer diameters of 8 mm and wall thicknesses of 1 mm to mimic an adult carotid artery. A different rubber mixture was used for each set of tubes, VytaFlex 10, VytaFlex20, and ReoFlex 30. Reference samples were also poured for testing with hyper-frequency viscoelastic spectroscopy (HFVS) instrument for measurement of the material complex modulus. Wave propagation measurements were made with a Verasonics system and linear array with water inside and surrounding the tubes. Acoustic radiation force was used to generate the Waves with a 200 µs push at 4.1 MHz and plane Wave imaging at a frame rate of 14.9 kHz was used for measuring the propagating Waves. A two-dimensional Fourier transform method was used to extract the Dispersion curves from the measured particle velocity. Theoretical Dispersion curves for flexural modes with circumferential Wavenumber n = 1, 2, 3 were calculated from the material properties measured with HFVS for comparison with the ultrasound-based results. The measured Dispersion curve matches well with theoretical results. However, the match is not with a single theoretical Dispersion curve, but with different theoretical curves at different frequencies. This new approach of matching with multiple theoretical curves can be used for better understanding of Wave propagation in arterial walls and improved characterization of their mechanical properties.
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measurement of viscoelastic properties of in vivo swine myocardium using lamb Wave Dispersion ultrasound vibrometry lduv
IEEE Transactions on Medical Imaging, 2013Co-Authors: Matthew W Urban, Ivan Z Nenadic, Cristina Pislaru, R R Kinnick, James F GreenleafAbstract:Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb Wave Dispersion ultrasound vibrometry (LDUV) is a shear Wave-based method that uses Wave velocity Dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical Waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of Wave propagation were measured over the 50-400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb Wave model to obtain estimates of the shear elasticity, μ1, and viscosity, μ2 as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb Wave model was also studied using simulated data. We demonstrated that Wave velocity measurements and Lamb Wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle.
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lamb Wave Dispersion ultrasound vibrometry lduv method for quantifying mechanical properties of viscoelastic solids
Physics in Medicine and Biology, 2011Co-Authors: Ivan Z Nenadic, Matthew W Urban, Scott Mitchell, James F GreenleafAbstract:Diastolic dysfunction is the inability of the left ventricle to supply sufficient stroke volumes under normal physiological conditions and is often accompanied by stiffening of the left-ventricular myocardium. A noninvasive technique capable of quantifying viscoelasticity of the myocardium would be beneficial in clinical settings. Our group has been investigating the use of shear Wave Dispersion ultrasound vibrometry (SDUV), a noninvasive ultrasound-based method for quantifying viscoelasticity of soft tissues. The primary motive of this study is the design and testing of viscoelastic materials suitable for validation of the Lamb Wave Dispersion ultrasound vibrometry (LDUV), an SDUV-based technique for measuring viscoelasticity of tissues with plate-like geometry. We report the results of quantifying viscoelasticity of urethane rubber and gelatin samples using LDUV and an embedded sphere method. The LDUV method was used to excite antisymmetric Lamb Waves and measure the Dispersion in urethane rubber and gelatin plates. An antisymmetric Lamb Wave model was fitted to the Wave speed Dispersion data to estimate elasticity and viscosity of the materials. A finite element model of a viscoelastic plate submerged in water was used to study the appropriateness of the Lamb Wave Dispersion equations. An embedded sphere method was used as an independent measurement of the viscoelasticity of the urethane rubber and gelatin. The FEM Dispersion data were in excellent agreement with the theoretical predictions. Viscoelasticity of the urethane rubber and gelatin obtained using the LDUV and embedded sphere methods agreed within one standard deviation. LDUV studies on excised porcine myocardium sample were performed to investigate the feasibility of the approach in preparation for open-chest in vivo studies. The results suggest that the LDUV technique can be used to quantify the mechanical properties of soft tissues with a plate-like geometry.
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shear Wave Dispersion ultrasonic vibrometry for measuring prostate shear stiffness and viscosity an in vitro pilot study
IEEE Transactions on Biomedical Engineering, 2011Co-Authors: F G Mitri, Matthew W Urban, Mostafa Fatemi, James F GreenleafAbstract:This paper reports shear stiffness and viscosity “virtual biopsy” measurements of the three excised noncancerous human prostates using a new tool known as shear Wave Dispersion ultrasound vibrometry (SDUV) in vitro. Improved methods for prostate guided-biopsy are required to effectively guide needle biopsy to the suspected site. In addition, tissue stiffness measurement helps in identifying a suspected site to perform biopsy because stiffness has been shown to correlate with pathologies, such as cancerous tissue. More importantly, early detection of prostate cancer may guide minimally invasive therapy and eliminate insidious procedures. In this paper, “virtual biopsies” were taken in multiple locations in three excised prostates; SDUV shear elasticity and viscosity measurements were performed at the selected “suspicious” locations within the prostates. SDUV measurements of prostate elasticity and viscosity are generally in agreement with preliminary values previously reported in the literature. It is, however, important to emphasize here that the obtained viscoelastic parameters values are local, and not a mean value for the whole prostate.
Xuewei Bao - One of the best experts on this subject based on the ideXlab platform.
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two crustal low velocity channels beneath se tibet revealed by joint inversion of rayleigh Wave Dispersion and receiver functions
Earth and Planetary Science Letters, 2015Co-Authors: Xiaoxiao Sun, Xuewei Bao, David W Eaton, Xiaodong Song, Liangshu Wang, Zhifeng Ding, Zhouchuan Huang, Pan WangAbstract:Abstract Competing geodynamic models, such as rigid-block extrusion, continuous deformation, and the mid-lower crustal flow, have been proposed to describe the growth and expansion of eastern Tibet. However, the dynamic processes responsible for plateau evolution and deformation remain poorly understood partly due to resolution limitations of previous models of lithospheric structure. On the basis of joint inversion of Rayleigh Wave Dispersion and receiver functions using data from a newly deployed seismic array, we have obtained a high-resolution 3D image that reveals the distribution of low-velocity zones (LVZs) with unprecedented clarity. The prominent feature of our model is two low-velocity channels that bound major strike-slip faults in SE Tibet and wrap around the Eastern Himalaya Syntaxis, consistent with the clockwise movement of crustal material in this region. Most large earthquakes in this region occurred in the boundaries of the LVZs. We propose that ductile flow within these channels, in addition to shear motion along strike-slip faults, played a significant role in accommodating intensive lithospheric deformation during the eastward expansion of Tibet in the Cenozoic.
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crustal structure beneath se tibet from joint analysis of receiver functions and rayleigh Wave Dispersion
Geophysical Research Letters, 2014Co-Authors: Xiaoxiao Sun, Xuewei Bao, David W Eaton, Xiaodong Song, Liangshu Wang, Zhifeng DingAbstract:New constraints on the pattern of crustal flow in SE Tibet are obtained from joint analysis of receiver functions and Rayleigh Wave Dispersion with a newly deployed seismic array. The crust in the Sichuan-Yunnan Diamond Block has an average thickness of ~45 km and gradually thins toward the Indo-China Block to the west and the Yangtze Block to the east. High VP/VS ratios are detected to the west of the Xiaojiang fault, but not in the Yangtze Block to the east. The S Wave velocity profile reveals that intra-crustal low-velocity zones (IC-LVZs) are strongly heterogeneous, with two LVZs in the middle and mid-lower crust, respectively, in marked contrast to previous observations of a single LVZ. Combined with other observations, the two IC-LVZs are interpreted as isolated channels of crustal flow at different depths beneath SE Tibet, resulting in the observed complex pattern of radial anisotropy and further elucidating patterns of flow and deformation.
Dariush Motazedian - One of the best experts on this subject based on the ideXlab platform.
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crustal shear Wave velocity models retrieved from rayleigh Wave Dispersion data in northern canada
Bulletin of the Seismological Society of America, 2014Co-Authors: Dariush MotazedianAbstract:Baffin Island is one of the several seismically active regions in the far north of Canada. In 1933, a strong earthquake with M w 7.3 occurred in the region. On 7 July 2009, a relatively strong earthquake with M w 6.0 occurred in the same area. This earthquake was very well recorded by many modern seismic stations. We systematically organized the Rayleigh‐Wave displacement records, measured Rayleigh‐Wave Dispersion data at 28 stations surrounding the epicenter, and retrieved the S ‐Wave velocity models. We used a previous model for the Western Quebec seismic zone as the initial model in our analyses and found that the velocities of all models at the shallow depths (<15 km) were obviously slower than those of the initial model. In the middle crust, the velocities in most models were close to those of the initial model. In the directions of azimuths 171°∼218° and 241°, the velocities in the middle crust were faster than those of the initial model. In the directions of 263°∼279°, the velocities in the middle crust were slower than those of the initial model. The slowest S ‐Wave velocities in the top layers occurred in the directions of azimuths 90° and 218°. These findings indicate differences in the existing crustal structures.
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crustal shear Wave velocity models retrieved from rayleigh Wave Dispersion data in northeastern north america
Bulletin of the Seismological Society of America, 2013Co-Authors: Dariush Motazedian, Stephen CraneAbstract:On 23 June 2010, a moderate earthquake with Mw 5.2 occurred near the town of Val-des-Bois, Quebec, Canada, ∼60 km northeast of Ottawa, Ontario. The earthquake generated excellent crustal Rayleigh-Wave records. We divided the 54 seismic stations that recorded clear Rayleigh-Wave trains into 14 groups by station azimuth. In each group, we measured the Rayleigh-Wave Dispersion data station by station and formed one Dispersion data file for the inversion. In this way, we ob- tained 14 crustal velocity models around the epicenter. We compared all 14 models and found that there are low-velocity layers in the top 10 km on the north side of the Ottawa-Bonnechere graben. Based on model similarity, we formed one model for the north side by averaging the north-side models and another model for the south side by averaging the south-side models. The separation of the north-side and south-side mod- els appears to follow the Ottawa-Bonnechere graben. In the top 10 km, the velocities in the south model are obviously slower than those in the north model.
Xiaodong Song - One of the best experts on this subject based on the ideXlab platform.
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two crustal low velocity channels beneath se tibet revealed by joint inversion of rayleigh Wave Dispersion and receiver functions
Earth and Planetary Science Letters, 2015Co-Authors: Xiaoxiao Sun, Xuewei Bao, David W Eaton, Xiaodong Song, Liangshu Wang, Zhifeng Ding, Zhouchuan Huang, Pan WangAbstract:Abstract Competing geodynamic models, such as rigid-block extrusion, continuous deformation, and the mid-lower crustal flow, have been proposed to describe the growth and expansion of eastern Tibet. However, the dynamic processes responsible for plateau evolution and deformation remain poorly understood partly due to resolution limitations of previous models of lithospheric structure. On the basis of joint inversion of Rayleigh Wave Dispersion and receiver functions using data from a newly deployed seismic array, we have obtained a high-resolution 3D image that reveals the distribution of low-velocity zones (LVZs) with unprecedented clarity. The prominent feature of our model is two low-velocity channels that bound major strike-slip faults in SE Tibet and wrap around the Eastern Himalaya Syntaxis, consistent with the clockwise movement of crustal material in this region. Most large earthquakes in this region occurred in the boundaries of the LVZs. We propose that ductile flow within these channels, in addition to shear motion along strike-slip faults, played a significant role in accommodating intensive lithospheric deformation during the eastward expansion of Tibet in the Cenozoic.
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crustal structure beneath se tibet from joint analysis of receiver functions and rayleigh Wave Dispersion
Geophysical Research Letters, 2014Co-Authors: Xiaoxiao Sun, Xuewei Bao, David W Eaton, Xiaodong Song, Liangshu Wang, Zhifeng DingAbstract:New constraints on the pattern of crustal flow in SE Tibet are obtained from joint analysis of receiver functions and Rayleigh Wave Dispersion with a newly deployed seismic array. The crust in the Sichuan-Yunnan Diamond Block has an average thickness of ~45 km and gradually thins toward the Indo-China Block to the west and the Yangtze Block to the east. High VP/VS ratios are detected to the west of the Xiaojiang fault, but not in the Yangtze Block to the east. The S Wave velocity profile reveals that intra-crustal low-velocity zones (IC-LVZs) are strongly heterogeneous, with two LVZs in the middle and mid-lower crust, respectively, in marked contrast to previous observations of a single LVZ. Combined with other observations, the two IC-LVZs are interpreted as isolated channels of crustal flow at different depths beneath SE Tibet, resulting in the observed complex pattern of radial anisotropy and further elucidating patterns of flow and deformation.
