Nonlinear response to ultrasound of encapsulated microbubbles

Abstract

The acoustic backscatter of encapsulated gas-filled microbubbles immersed in a weak compressible liquid and irradiated by ultrasound fields of moderate to high pressure amplitudes is investigated theoretically. The problem is formulated by considering, for the viscoelastic shell of finite thickness, an isotropic hyperelastic neo-Hookean model for the elastic contribution in addition to a Newtonian viscous component. First and second harmonic scattering cross-sections have been evaluated and the quantitative influence of the driving pressure amplitude on the harmonic resonance frequencies for different initial equilibrium bubble sizes and for different encapsulating physical properties has been determined. Conditions for optimal second harmonic imaging have been also investigated and some regions in the parameters space where the second harmonic intensity is dominant over the fundamental have been identified. Results have been obtained for albumin, lipid and polymer encapsulating shells, respectively.

Intelligent controlling microbubble radial oscillations by using Slave–Master Feedback control

“…From the results, it can be understood that the motions of microbubble can be chaotic or stable in particular ranges. The results are in agreement with the previous studies, clearly highlighting that microbubbles are dependent on the driving frequency variations [35,[41][42][43]. Most of the results demonstrate the uncontrollable and chaotic motion in UCA microbubble dynamics.…”

“…It belongs to a microbubble with initial radius of 5 lm exposed to a frequency of the acoustic force of 2 MHz when the control parameter is pressure in the range of 10 kPa-4 MPa (a condition used typically during HIFU [62,63]). It is easily understood that by increasing pressure amplitudes the microbubble stability is reduced and chaotic oscillations will be obvious which can be proved by previous studies [35,[40][41][42][43]. In order to study the possibility of reducing chaos in oscillation of UCA microbubble, a dynamical control method is applied.…”

“…In recent years, the explanation of the modern methods of nonlinear dynamical systems has been developed in recognizing the nonlinear behavior of microbubbles and encapsulated microbubbles [35,[40][41][42][43]. Lately, researchers give more attention to this investigation, so that the study of their behavior has recently been the center of attention.…”

Targeted ultrasound contrast agents for ultrasound molecular imaging and therapy

“…However, performance of these imaging methods is degraded because the excitation frequency is much higher than the resonance frequency of the MBs, attenuation is higher, and far-wall artefacts are a big challenge to overcome [112][113][114][115][116]. Therefore, improved imaging methods have been extensively studied, such as improved harmonic imaging methods [117][118][119], chirp coded excitation alone [120,121] or combined with pulse inversion [122,123]. Among the non-linear components of the MB response the SH signal has drawn much attention lately, due to its MB specificity and artefact-free characteristics.…”

Effect of magnetic field on the radial pulsations of a gas bubble in a non-Newtonian fluid

“…In recent years, the explanation of the modern methods of nonlinear dynamic systems has been developed in recognizing the nonlinear behaviors of bubbles and encapsulated microbubbles [56][57][58][59][60]. Lately, researchers have been giving more attention to the investigation of these behaviors.…”