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Alavi M.,University of Montreal | Destrempes F.,University of Montreal | Schmitt C.,Rheolution Inc | Montagnon E.,University of Montreal | Cloutier G.,University of Montreal
IEEE International Ultrasonics Symposium, IUS | Year: 2012

In the context of tissue characterization, one may wonder what does the consideration of a quantitative ultrasound (QUS) feature of a medium under the propagation of a shear wave (SW) add to its discriminant power. This study presents the time-varying behavior of the K-distribution beta parameter-the reciprocal of the effective density of scatterers-under SW propagation and its relation with the viscoelasticity of the medium. Transient plane SW at 300 Hz central frequency was transmitted to three agar-gelatin phantoms at different concentrations. The amplitude of the B-mode backscatter echoes acquired with an 8 MHz probe was modeled with the K-distribution. The normalized range of beta (i.e., its range normalized by its mean value as the SW propagates) was determined by considering the B-mode images during SW propagation. Also, the storage (G′) and loss (G″) moduli of each phantom were measured on samples with the RheoSpectris hyper-frequency instrument (Rheolution, Montreal, Canada). The time-evolution of the beta parameter and displacements (using cross-correlation) within tissue-mimicking phantoms under SW vibration suggest that the beta parameter can be used to track SW propagation. In-vitro results showed that the normalized range of beta is related to the viscoelasticity of phantoms. By increasing G′ and G″, the normalized range of beta decreased. Thus, the consideration of the behavior of beta under SW propagation modifies the effective density of scatterers with respect to static conditions (i.e., without SW). This is new observation and a new step towards understanding statistical QUS behavior. © 2012 IEEE. Source


Ekeom D.,University of Montreal | Henni A.,University of Montreal | Henni A.,Rheolution Inc | Cloutier G.,University of Montreal
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2013

This work demonstrates, with numerical simulations, the potential of an octagonal probe for the generation of radiation forces in a set of points following a path surrounding a breast lesion in the context of dynamic ultrasound elastography imaging. Because of the in-going wave adaptive focusing strategy, the proposed method is adapted to induce shear wave fronts to interact optimally with complex lesions. Transducer elements were based on 1-3 piezocomposite material. Threedimensional simulations combining the finite element method and boundary element method with periodic boundary conditions in the elevation direction were used to predict acoustic wave radiation in a targeted region of interest. The coupling factor of the piezocomposite material and the radiated power of the transducer were optimized. The transducer's electrical impedance was targeted to 50 Ω. The probe was simulated by assembling the designed transducer elements to build an octagonal phased-array with 256 elements on each edge (for a total of 2048 elements). The central frequency is 4.54 MHz; simulated transducer elements are able to deliver enough power and can generate the radiation force with a relatively low level of voltage excitation. Using dynamic transmitter beamforming techniques, the radiation force along a path and resulting acoustic pattern in the breast were simulated assuming a linear isotropic medium. Magnitude and orientation of the acoustic intensity (radiation force) at any point of a generation path could be controlled for the case of an example representing a heterogeneous medium with an embedded soft mechanical inclusion. © 1986-2012 IEEE. Source


Ouared A.,University of Montreal | Montagnon E.,University of Montreal | Montagnon E.,Rheolution Inc | Cloutier G.,University of Montreal
IEEE International Ultrasonics Symposium, IUS | Year: 2014

In remote dynamic elastography, amplitudes of generated displacement fields are directly related to the amplitude of the radiation force. Therefore, displacement improvement for better tissue characterization requires the optimization of the radiation force by increasing the push duration and/or the excitation amplitude of the transducer. The main problem of this approach is that the Food and Drug Administration (FDA) thresholds for medical applications, and transducer limitations may be easily exceeded. In the present study, the effect of the frequency used for the generation of radiation force on the amplitude of the displacement field is investigated. The aim is to apply the adaptive radiation force to increase the displacement amplitude. We found that amplitudes of displacements generated by adapted radiation force sequences are greater than those generated by non-adapted ones. The obtained gains were between 20% and 158% depending on the focus depths and the attenuation of the tested phantom. The signal to noise ratio was also improved by more than four times. We conclude that frequency adaptation is a complementary technique that may be used for the optimization of displacement amplitude. This technique can be used safely to optimize the deposited local acoustic energy, without increasing the risk of damaging tissues and transducers. © 2014 IEEE. Source


Ouared A.,University of Montreal | Montagnon E.,University of Montreal | Montagnon E.,Rheolution Inc | Kazemirad S.,University of Montreal | And 3 more authors.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2015

In remote dynamic elastography, the amplitude of the generated displacement field is directly related to the amplitude of the radiation force. Therefore, displacement improvement for better tissue characterization requires the optimization of the radiation force amplitude by increasing the push duration and/or the excitation amplitude applied on the transducer. The main problem of these approaches is that the Food and Drug Administration (FDA) thresholds for medical applications and transducer limitations may be easily exceeded. In the present study, the effect of the frequency used for the generation of the radiation force on the amplitude of the displacement field was investigated. We found that amplitudes of displacements generated by adapted radiation force sequences were greater than those generated by standard nonadapted ones (i.e., single push acoustic radiation force impulse and supersonic shear imaging). Gains in magnitude were between 20 to 158% for in vitro measurements on agar-gelatin phantoms, and 170 to 336% for ex vivo measurements on a human breast sample, depending on focus depths and attenuations of tested samples. The signal-to-noise ratio was also improved more than 4-fold with adapted sequences. We conclude that frequency adaptation is a complementary technique that is efficient for the optimization of displacement amplitudes. This technique can be used safely to optimize the deposited local acoustic energy without increasing the risk of damaging tissues and transducer elements. © 1986-2012 IEEE. Source


Ouared A.,University of Montreal | Montagnon E.,University of Montreal | Montagnon E.,Rheolution Inc | Cloutier G.,University of Montreal
Physics in Medicine and Biology | Year: 2015

A method based on adaptive torsional shear waves (ATSW) is proposed to overcome the strong attenuation of shear waves generated by a radiation force in dynamic elastography. During the inward propagation of ATSW, the magnitude of displacements is enhanced due to the convergence of shear waves and constructive interferences. The proposed method consists in generating ATSW fields from the combination of quasi-plane shear wavefronts by considering a linear superposition of displacement maps. Adaptive torsional shear waves were experimentally generated in homogeneous and heterogeneous tissue mimicking phantoms, and compared to quasi-plane shear wave propagations. Results demonstrated that displacement magnitudes by ATSW could be up to 3 times higher than those obtained with quasi-plane shear waves, that the variability of shear wave speeds was reduced, and that the signal-to-noise ratio of displacements was improved. It was also observed that ATSW could cause mechanical inclusions to resonate in heterogeneous phantoms, which further increased the displacement contrast between the inclusion and the surrounding medium. This method opens a way for the development of new noninvasive tissue characterization strategies based on ATSW in the framework of our previously reported shear wave induced resonance elastography (SWIRE) method proposed for breast cancer diagnosis. © 2015 Institute of Physics and Engineering in Medicine. Source

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