A finite-element method model of soft tissue response to impulsive acoustic radiation force

Abstract

Several groups are studying acoustic radiation force and its ability to image the mechanical properties of tissue. Acoustic radiation force impulse (ARFI) imaging is one modality using standard diagnostic ultrasound scanners to generate localized, impulsive, acoustic radiation forces in tissue. The dynamic response of tissue is measured via conventional ultrasonic speckle-tracking methods and provides information about the mechanical properties of tissue. A finite-element method (FEM) model has been developed that simulates the dynamic response of tissues, with and without spherical inclusions, to an impulsive acoustic radiation force excitation from a linear array transducer. These FEM models were validated with calibrated phantoms. Shear wave speed, and therefore elasticity, dictates tissue relaxation following ARFI excitation, but Poisson's ratio and density do not significantly alter tissue relaxation rates. Increased acoustic attenuation in tissue increases the relative amount of tissue displacement in the near field compared with the focal depth, but relaxation rates are not altered. Applications of this model include improving image quality, and distilling material and structural information from tissue's dynamic response to ARFI excitation. Future work on these models includes incorporation of viscous material properties and modeling the ultrasonic tracking of displaced scatterers.

Quantifying Hepatic Shear Modulus In Vivo Using Acoustic Radiation Force

“…These shear moduli represent those reported for healthy through cirrhotic livers (Foucher et al, 2006;Sandrin et al, 2003). These models have been previously validated to accurately simulate shear waves that are generated in response to impulsive acoustic radiation force excitations in elastic media (Palmeri et al, 2005). Table 1 outlines the simulated excitation beam configuration.…”

“…The Lateral TTP algorithm was applied to ARFI shear wave data obtained in a gelatin tissuemimicking phantom (Hall T.J. et al, 1997;Palmeri et al, 2005). Two-dimensional (2D) images of reconstructed shear moduli, as shown in Figure 6, were made using the Lateral TTP algorithm.…”

Effect of Ultrafast Imaging on Shear Wave Visualization and Characterization: An Experimental and Computational Study in a Pediatric Ventricular Model

“…The volume force acts throughout the complete thickness of the PVA phantom in this focal region, whereas the interface pressure is only active on the interfaces between phantom and water. Volume force and interface pressure are calculated based on the time-averaged acoustic intensity , of which its spatial distribution is derived by simulating acoustic probe pressures mimicking the push sequence (see Table 1) with Field II and its magnitude is scaled to 1500 W/cm 2 [26], as follows [21,27]: …”

“…As actual SWE experiments do not provide access to a ground truth for imaged shear wave propagation, a multiphysics modeling approach combining computational solid mechanics (CSM) of the shear wave propagation [20][21][22] with ultrasound (US) modeling of ultrafast imaging was used for this purpose. The resulting wave mechanics from CSM provided the true mechanical shear wave propagation whereas the virtual images represented the imaged shear wave propagation.…”

A finite element model to study the effect of tissue anisotropy onex vivoarterial shear wave elastography measurements

“…This approach allows to have full control over the arterial architecture, mechanical properties and the excited ARF (Lee et al, 2012;Palmeri et al, 2005;Caenen et al, 2015). By varying the fibre orientation and the probe orientation in the numerical model, we will verify whether elasticity variations due to stretch-induced stiffening are indeed picked up most easily when the transducer is (close to) parallel to the fibre orientation, i.e.…”