An iterative fullwave simulation approach to multiple scattering in media with randomly distributed microbubbles

Abstract

Ultrasound contrast agents (UCA), such as microbubbles, enhance the scattering properties of blood, which is otherwise hypoechoic. The multiple scattering interactions of the acoustic field with UCA are poorly understood due to the complexity of the multiple scattering theories and the nonlinear microbubble response. The majority of bubble models describe the behavior of UCA as single, isolated microbubbles suspended in infinite medium. Multiple scattering models such as the independent scattering approximation can approximate phase velocity and attenuation for low scatterer volume fractions. However, all current models and simulation approaches only describe multiple scattering and nonlinear bubble dynamics separately. Here we present an approach that combines two existing models: (1) a full-wave model that describes nonlinear propagation and scattering interactions in a heterogeneous attenuating medium and (2) a Paul–Sarkar model that describes the nonlinear interactions between an acoustic field and microbubbles. These two models were solved numerically and combined with an iterative approach. The convergence of this combined model was explored in silico for 0.5 × 106 microbubbles ml−1, 1% and 2% bubble concentration by volume. The backscattering predicted by our modeling approach was verified experimentally with water tank measurements performed with a 128-element linear array transducer. An excellent agreement in terms of the fundamental and harmonic acoustic fields is shown. Additionally, our model correctly predicts the phase velocity and attenuation measured using through transmission and predicted by the independent scattering approximation.

Modeling ultrasound propagation in the moving brain: applications to shear shock waves and traumatic brain injury

“…The proposed method can be used generally to model different types of motion or deformation including tissue motion due linear shear waves in elastography or physiological motion with applications to motion filtering. This method can be applied to the larger body of work in finite difference simulations so that small displacements can be modeled in the context of ultrasound imaging, phase aberration, reverberation, focused ultrasound, multiple scattering in bubbly media, coherence imaging, etc [14], [27]- [29]. Besides ultrasound imaging, the technique can be applied to applications involving small displacement of any physical quantity such as stress, strain, temperature or electric potential.…”

“…The Fullwave tool has been used to generate highly realistic ultrasound images, to study the sources of image degradation [27], [28] and to understand the principles behind new imaging methods, such as short lag spatial coherence imaging [6], [29]. It has also been used to simulate how elements that are blocked by ribs can degrade image quality [13] and to describe multiple scattering due to microbubble contrast agents [14]. This simulation approach has been used to successfully model human transcranial focused ultrasound therapy of the brain.…”

Toward Noninvasive Mapping of Diffuse Scattering in the Presence of Motion

“…15,16 These approaches rely on acquisition of an interelement response (IR) matrix (i.e., responses between every pair of transmit and receive elements), followed by separation of coherent and incoherent contributions to the received signal, with the incoherent contributions corresponding to the diffusive regime. [15][16][17][18] In this article, we present the first attempt to translate coda wave analysis techniques to medical ultrasound arrays to develop two-dimensional (2D) mapping of diffuse scattering due to motion-induced decorrelation. In this work, the developed approach is presented along with experiments using single-element and diverging wave transmit events in tissue-mimicking phantoms and in ex vivo cardiac samples.…”