Nonlinear Oscillations Of Microbubbles Research Articles

Effect of Pulse Shaping on Subharmonic Aided Pressure Estimation In Vitro and In Vivo.

Subharmonic imaging (SHI) is a technique that uses the nonlinear oscillations of microbubbles when exposed to ultrasound at high pressures transmitting at the fundamental frequency ie, fo and receiving at half the transmit frequency (ie, fo /2). Subharmonic aided pressure estimation (SHAPE) is based on the inverse relationship between the subharmonic amplitude of the microbubbles and the ambient pressure change. Eight waveforms with different envelopes were optimized with respect to acoustic power at which the SHAPE study is most sensitive. The study was run with four input transmit cycles, first in vitro and then in vivo in three canines to select the waveform that achieved the best sensitivity for detecting changes in portal pressures using SHAPE. A Logiq 9 scanner with a 4C curvi-linear array was used to acquire 2.5 MHz radio-frequency data. Scanning was performed in dual imaging mode with B-mode imaging at 4 MHz and a SHI contrast mode transmitting at 2.5 MHz and receiving at 1.25 MHz. Sonazoid, which is a lipid stabilized gas filled bubble of perfluorobutane, was used as the contrast agent in this study. A linear decrease in subharmonic amplitude with increased pressure was observed for all waveforms (r from -0.77 to -0.93; P < .001) in vitro. There was a significantly higher correlation of the SHAPE gradient with changing pressures for the broadband pulses as compared to the narrowband pulses in both in vitro and in vivo results. The highest correlation was achieved with a Gaussian windowed binomial filtered square wave with an r-value of -0.95. One of the three canines was eliminated for technical reasons, while the other two produced very similar results to those obtained in vitro (r from -0.72 to -0.98; P <.01). The most consistent in vivo results were achieved with the Gaussian windowed binomial filtered square wave (r = -0.95 and -0.96). Using this waveform is an improvement to the existing SHAPE technique (where a square wave was used) and should make SHAPE more sensitive for noninvasively determining portal hypertension.

Ultrasound modulated optical tomography contrast enhancement with non-linear oscillation of microbubbles.

Ultrasound modulated optical tomography (USMOT) is an imaging technique used to provide optical functional information inside highly scattering biological tissue. One of the challenges facing this technique is the low image contrast. A contrast enhancement imaging technique based on the non-linear oscillation of microbubbles is demonstrated to improve image contrast. The ultrasound modulated signal was detected using a laser pulse based speckle contrast detection system. Better understanding of the effects of microbubbles on the optical signals was achieved through simultaneous measurement of the ultrasound scattered by the microbubbles. The length of the laser pulse was found to affect the system response of the speckle contrast method with shorter pulses suppressing the fundamental ultrasound modulated optical signal. Using this property, image contrast can be enhanced by detection of the higher harmonic ultrasound modulated optical signals due to nonlinear oscillation and destruction of the microbubbles. Experimental investigations were carried out to demonstrate a doubling in contrast by imaging a scattering phantom containing an embedded silicone tube with microbubbles flowing through it. The contrast enhancement in USMOT resulting from the use of ultrasound microbubbles has been demonstrated. Destruction of the microbubbles was shown to be the dominant effect leading to contrast improvement as shown by simultaneously detecting the ultrasound and speckle contrast signals. Line scans of a microbubble filled silicone tube embedded in a scattering phantom demonstrated experimentally the significant image contrast improvement that can be achieved using microbubbles and demonstrates the potential as a future clinical imaging tool.

J026024 液体の温度上昇に及ぼすマイクロバブルの非線形振動の影響

J026024 液体の温度上昇に及ぼすマイクロバブルの非線形振動の影響

Relaxation Behavior of Microbubbles in Ultrasonic Field

The nonlinear oscillation of microbubbles under the influence of ultrasound was investigated experimentally and theoretically. The radius-time curves of bubbles including afterbounces calculated using the Rayleigh–Plesset equation with polytropic relations and with the Keller–Miksis equation using analytical solutions for the Navier–Stokes equations of the gases were compared with the results observed from light scattering. This study revealed that the dynamic behavior of microbubbles in an ultrasonic field, such as the expansion ratio of the maximum to the equilibrium radius and the bouncing motion after the first collapse (minimum), depends crucially on the relaxation time of the bubble motion with respect to the characteristic time of the applied ultrasound, and that the relaxation time decreases as the equilibrium radius of the microbubbles increases.

Acoustical correction to the bubble dynamics equation for elastic media

Nonlinear oscillations of microbubbles are being investigated extensively for innovative medical and industrial applications. The Rayleigh–Plesset equation successfully describes the dynamics of gas bubbles in liquids and viscoelastic media. To model bubble dynamics in weakly compressible elastic media such as soft tissue, effects of shear stress should be taken into account. These effects were included recently by the authors in a model for bubble oscillations that differs from the Rayleigh–Plesset equation by a single term associated with nonlinear elasticity of the medium surrounding the bubble. Here, we augment this dynamical equation to account for acoustic radiation and thus describe nonlinear bubble oscillations in slightly compressible elastic media. The bubble is assumed to be spherical and the surrounding elastic medium to be isotropic. The analysis is performed in Eulerian coordinates, and attention is devoted to terms associated with radiation loss. Our analysis builds on results obtained by Prosperetti and Lezzi [J. Fluid Mech. 168, 457 (1986)] for a bubble in liquid. The stress tensor for the elastic medium is expressed through invariants of the Green deformation tensor in spherical coordinates. Explicit expressions for components of the stress tensor are obtained using Mooney’s potential function. [Work supported by IR&amp;D at ARL:UT.]

Effect of Micro-Bubbles in Water on Beam Patterns of Parametric Array

The improvement in efficiency of a parametric array by nonlinear oscillation of micro-bubbles in water is studied in this paper. The micro-bubble oscillation can increase the nonlinear coefficient of the acoustic medium. The amplitude of the difference-frequency wave along the longitudinal axis and its beam patterns in the field including the layer with micro-bubbles were analyzed using a Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation. As a result, the largest improvement in efficiency was obtained and a narrow parametric beam was formed by forming a layer with micro-bubbles in front of a parametric sound radiator as thick as about the shock formation distance. If the layer becomes significantly thicker than the distance, the beam of the difference-frequency wave in the far-field will become broader. If the layer is significantly thinner than the distance, the intensity level of the wave in the far-field will be too low.