Development of high intensity focused ultrasound simulator for large‐scale computing

Abstract

SUMMARYHigh intensity focused ultrasound (HIFU) has been developed as a noninvasive therapeutic option. HIFU simulations are required to support the development of the HIFU device as well as the realization of noninvasive treatments. In this study, an HIFU simulator is developed that uses voxel data constructed from computed tomography scan data on the living human body and signed distance function (SDF) data to represent the object. The HIFU simulator solves the conservation equations of mass and momentum for mixtures with the equation of state for each medium. The numerical method is the finite-difference timedomain method. A high-order finite-difference method based on Lagrange interpolation is implemented to reduce numerical phase error. This approach reproduces wave propagation to an nth order of accuracy. Representation of the sound source by volume fraction, which is obtained from the SDF using a smoothed Heaviside function, provides around 1.66th order of accuracy in the spherical wave problem. As a realistic application, transcranial HIFU therapy for a brain tumor is modeled, where tissue inhomogeneity causes not only displacement of the focal point but also diffusion of the focused ultrasound. Even in such cases, focus control using phase delays, which are pre-computed based on the time-reversal procedure, enables correct focal point targeting as well as improved ultrasound focusing.

Multiphysics computational models for cardiac flow and virtual cardiography

“…By solving Equation , the wave transmission and reflection at the interface between the blood flow and tissue are automatically resolved based on the difference of acoustic impedance Z = K / c . In this model, the propagation of shear waves in the tissue material is not considered, because the shear modulus of the tissue materials is much smaller than the bulk modulus . Also, the dissipation of the acoustic wave is neglected because the frequency range of the heart sound is typically low ( ∼ O(100) Hz), and the dissipation for these low frequencies is expected to be very small.…”

“…Also, the dissipation of the acoustic wave is neglected because the frequency range of the heart sound is typically low ( ∼ O(100) Hz), and the dissipation for these low frequencies is expected to be very small. The current fluid‐like assumption of the tissue material for the purpose of resolving acoustic wave propagation has been widely used for the simulation of sound wave propagation in biological materials . The present approach has also been used for the direct computation of arterial bruits .…”

Fourier continuation methods for high-fidelity simulation of nonlinear acoustic beams

“…V. For added efficiency, the solver was specialized to exploit certain properties of the solution, namely reflection symmetry and the limited temporal duration of the waveform implicit in Eq. (23). (Note, however, that in Sec.…”

“…However, as computing technology has become increasingly powerful, there has been a renewed interest in solving full-wave models (e.g., Navier-Stokes or Westervelt equations). 7,[17][18][19][20][21][22][23][24] One reason for developing improved computational methodologies, therefore, is to enable the use of less restrictive HIFU models in practice. Moreover, the development of advanced computational algorithms is useful in the field of HIFU simulation as a whole.…”

A source term approach for generation of one-way acoustic waves in the Euler and Navier–Stokes equations

“…For many applications, a source of acoustic waves is modeled as an oscillating surface. Treating the source surface as a real oscillating surface requires either body-fitted grids or immersed boundary/surface techniques, see for example [4, 5, 6]. In many cases, however, the surface itself is irrelevant to the ensuing dynamics, and we therefore seek an immersed, volumetric representation of acoustic waves produced at such an immersed surface, but without explicitly modeling the surface as a boundary condition.…”