Shear wave attenuation measurement of tissue-mimicking materials using a two-point frequency shift method

2019 ◽  
Vol 146 (4) ◽  
pp. 3071-3071
Author(s):  
Piotr Kijanka ◽  
Matthew W. Urban
Keyword(s):  
Frequency Shift ◽  
Shear Wave ◽  
Wave Attenuation ◽  
Shift Method ◽  
Attenuation Measurement

scholarly journals Lorentz force induced shear waves for magnetic resonance elastography applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Guillaume Flé ◽  
Guillaume Gilbert ◽  
Pol Grasland-Mongrain ◽  
Guy Cloutier
Keyword(s):  
Magnetic Resonance ◽  
Shear Wave ◽  
Lorentz Force ◽  
Wave Attenuation ◽  
Shear Waves ◽  
Estimation Method ◽  
Biological Tissues ◽  
Magnetic Resonance Elastography ◽  
Motion Generation ◽  
Wave Source

AbstractQuantitative mechanical properties of biological tissues can be mapped using the shear wave elastography technique. This technology has demonstrated a great potential in various organs but shows a limit due to wave attenuation in biological tissues. An option to overcome the inherent loss in shear wave magnitude along the propagation pathway may be to stimulate tissues closer to regions of interest using alternative motion generation techniques. The present study investigated the feasibility of generating shear waves by applying a Lorentz force directly to tissue mimicking samples for magnetic resonance elastography applications. This was done by combining an electrical current with the strong magnetic field of a clinical MRI scanner. The Local Frequency Estimation method was used to assess the real value of the shear modulus of tested phantoms from Lorentz force induced motion. Finite elements modeling of reported experiments showed a consistent behavior but featured wavelengths larger than measured ones. Results suggest the feasibility of a magnetic resonance elastography technique based on the Lorentz force to produce an shear wave source.

scholarly journals ACOUSTIC SEISMIC WAVE ATTENUATION IN ROCKS: ESTIMATES INSTABILITIES, FREQUENCY-DEPENDENCE AND INCOHERENCES

2017 ◽  
Vol 35 (3) ◽  
Author(s):  
Julián David Peláez ◽  
Luis Alfredo Montes
Keyword(s):  
Frequency Shift ◽  
Seismic Wave ◽  
Wave Attenuation ◽  
Spectral Ratio ◽  
Well Logs ◽  
Well Log ◽  
Seismic Profiles ◽  
Seismic Wave Attenuation ◽  
Transmission Coefficients ◽  
Centroid Frequency

ABSTRACT. Seismic wave attenuation (Q−1) values indicate relevant media properties, such as fluid content and porosity. Q−1 estimates, obtained using both VSP and conventional well log data, did not exhibit comparable trends, nor values. Whereas VSP results represent total attenuation, well log Q−1, which, theoretically, should represent scattering losses, displayed a low percentage correlation with transmission coefficients and other well logs. The influence of processing routines, chosen methodology and input parameters on Q−1-values suggests that ASR (Amplitude Spectral Ratio) and CFS (Centroid Frequency Shift) attenuation estimates should be regarded, in practical terms, as relative quantities instead of absolute ones. Seemingly incoherent negative values are frequent, nonetheless these could hold a physical meaning related to elastic amplification at interfaces. Considering that quality factor (Q) values obtained were more unstable than Q−1-values, it is advisable to report the latter. Keywords: Vertical Seismic Profiles, well logs, transmission coefficients, scattering, amplification.RESUMO. Os valores de atenuação da onda sísmica (Q−1) indicam propriedades relavantes dos meios, tais como conteúdo de fluido e porosidade. As estimativas do Q−1, obtidas usando dados de VSP e dados de poços convencionais, não apresentaram tendências nem valores comparáveis. Enquanto os resultados de VSP representamatenuação total, os resultados dos dados de poços, que teoricamente deveriam representar perdas de dispersão, apresentaramuma baixa correlação percentual com os coeficientes de transmissão e outros dados de poços. A influência das rotinas de processamento, da metodologia escolhida e dos parâmetros de entrada nos valores Q−1 sugere que as estimativas de atenuação ASR (Amplitude Spectral Ratio) e CFS (Centroid Frequency Shift) devem ser, em termos práticos, consideradas como quantidades relativas em vez de absolutas. Valores negativos aparentemente incoerentes são frequentes, no entanto estes poderiam conter um significado físico relacionado `a amplificação elástica nas interfaces. Considerando que os valores do fator de qualidade (Q) obtidos foram mais instáveis do que os valores de Q−1, é aconselhável documentar o último. Palavras-chave: Perfis Sísmicos Verticais, registros de poços, coeficientes de transmissão, dispersão, amplificação.

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