The Experts below are selected from a list of 7287 Experts worldwide ranked by ideXlab platform
Dorothea I Hollnagel - One of the best experts on this subject based on the ideXlab platform.
-
comparative velocity investigations in cerebral arteries and aneurysms 3d phase contrast mr angiography Laser Doppler Velocimetry and computational fluid dynamics
NMR in Biomedicine, 2009Co-Authors: Dorothea I Hollnagel, Paul Summers, Dimos Poulikakos, Spyros KolliasAbstract:In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3 Tesla MR scanner, Laser Doppler Velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field. Copyright © 2009 John Wiley & Sons, Ltd.
-
comparative velocity investigations in cerebral arteries and aneurysms 3d phase contrast mr angiography Laser Doppler Velocimetry and computational fluid dynamics
NMR in Biomedicine, 2009Co-Authors: Dorothea I Hollnagel, Paul Summers, Dimos Poulikakos, Spyros KolliasAbstract:In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3 Tesla MR scanner, Laser Doppler Velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field.
Spyros Kollias - One of the best experts on this subject based on the ideXlab platform.
-
comparative velocity investigations in cerebral arteries and aneurysms 3d phase contrast mr angiography Laser Doppler Velocimetry and computational fluid dynamics
NMR in Biomedicine, 2009Co-Authors: Dorothea I Hollnagel, Paul Summers, Dimos Poulikakos, Spyros KolliasAbstract:In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3 Tesla MR scanner, Laser Doppler Velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field. Copyright © 2009 John Wiley & Sons, Ltd.
-
comparative velocity investigations in cerebral arteries and aneurysms 3d phase contrast mr angiography Laser Doppler Velocimetry and computational fluid dynamics
NMR in Biomedicine, 2009Co-Authors: Dorothea I Hollnagel, Paul Summers, Dimos Poulikakos, Spyros KolliasAbstract:In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3 Tesla MR scanner, Laser Doppler Velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field.
Paul Summers - One of the best experts on this subject based on the ideXlab platform.
-
comparative velocity investigations in cerebral arteries and aneurysms 3d phase contrast mr angiography Laser Doppler Velocimetry and computational fluid dynamics
NMR in Biomedicine, 2009Co-Authors: Dorothea I Hollnagel, Paul Summers, Dimos Poulikakos, Spyros KolliasAbstract:In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3 Tesla MR scanner, Laser Doppler Velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field. Copyright © 2009 John Wiley & Sons, Ltd.
-
comparative velocity investigations in cerebral arteries and aneurysms 3d phase contrast mr angiography Laser Doppler Velocimetry and computational fluid dynamics
NMR in Biomedicine, 2009Co-Authors: Dorothea I Hollnagel, Paul Summers, Dimos Poulikakos, Spyros KolliasAbstract:In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3 Tesla MR scanner, Laser Doppler Velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field.
Kenju Otsuka - One of the best experts on this subject based on the ideXlab platform.
-
self mixing thin slice solid state Laser Doppler Velocimetry with much less than one feedback photon per Doppler cycle
Optics Letters, 2015Co-Authors: Kenju OtsukaAbstract:The drastic shortening of a photon lifetime as compared with normal TEM00 operations has been shown to be associated with the formation of annular mode operations in a thin-slice Nd:GdVO4 Laser with tilted Laser diode end pumping. The 15 dB enhancement of the signal-to-noise ratio, owing to the shortened photon lifetime, has been demonstrated in the self-mixing Laser Doppler Velocimetry experiment in comparison with the TEM00 operations, where the minimum intensity feedback rate from a target to the Laser for successful measurements was estimated to be −123 dB, which corresponds to 0.007 photon per Doppler cycle.
-
analysis of molecular dynamics of colloidal particles in transported dilute samples by self mixing Laser Doppler Velocimetry
Applied Optics, 2012Co-Authors: Seiichi Sudo, Takayuki Ohtomo, Masao Iwamatsu, Tuyoshi Osada, Kenju OtsukaAbstract:Colloidal particles in a liquid medium are transported with constant velocity, and dynamic light scattering experiments are performed on the samples by self-mixing Laser Doppler Velocimetry. The power spectrum of the modulated wave induced by the motion of the colloidal particles cannot be described by the well-known formula for flowing Brownian motion systems, i.e., a combination of Doppler shift, diffusion, and translation. Rather, the power spectrum was found to be described by the q-Gaussian distribution function. The molecular mechanism resulting in this anomalous line shape of the power spectrum is attributed to the anomalous molecular dynamics of colloidal particles in transported dilute samples, which satisfy a nonlinear Langevin equation.
-
ultrahigh sensitivity self mixing Laser Doppler Velocimetry with Laser diode pumped microchip lindp sub 4 o sub 12 Lasers
IEEE Photonics Technology Letters, 1999Co-Authors: R Kawai, Y Asakawa, Kenju OtsukaAbstract:A self-mixing Laser Doppler Velocimetry (LDV) has been demonstrated with Laser-diode-pumped microcavity LiNdP/sub 4/O/sub 12/ Lasers. The feedback signal required for a usable measurement without using photon-correlation techniques was <1 photon per Doppler-beat cycle. An enhancement of LDV signals by resonant excitations of relaxation oscillations has been performed.
-
ultrahigh sensitivity Laser Doppler Velocimetry with a microchip solid state Laser
Applied Optics, 1994Co-Authors: Kenju OtsukaAbstract:Highly sensitive Laser Doppler Velocimetry featuring the simultaneous measurement of light-scattering objects moving at different velocities and vibration sensing based on Doppler-shifted light-injectioninduced intensity modulation in an externally pumped microchip solid-state Laser is demonstrated.
Robert L Shambaugh - One of the best experts on this subject based on the ideXlab platform.
-
experimental measurements of fiber threadline vibrations in the melt blowing process
Industrial & Engineering Chemistry Research, 1996Co-Authors: Rajeev Chhabra, Robert L ShambaughAbstract:The motion of a melt-blown fiber was experimentally measured. After exiting the spinning die, a melt-blown fiber was found to vibrate with frequencies and amplitudes that were functions of the operating conditions (polymer flow rate, polymer temperature, air flow rate, and air temperature). Fiber amplitude was measured with both multiple-image flash photography and Laser Doppler Velocimetry. Fiber frequency was measured with Laser Doppler Velocimetry.
-
characterization of the melt blowing process with Laser Doppler Velocimetry
Industrial & Engineering Chemistry Research, 1992Co-Authors: Robert L ShambaughAbstract:Laser Doppler Velocimetry (LVD) was used to study the process of melt blowing. For an array of positions below the melt blowing die, LVD measurements were made on the fiber velocities in three-space. This information quantifies the existence of an expanding cone of fibers below the melt blowing die. Through the use of correlation function developed in this work, one can determine the actual rate of fibers passing through a specified area below the melt blowing die
