Coupling of finite difference elastodynamic and semi-analytic Rayleigh integral codes for the modeling of ultrasound propagation at the hip

Abstract

Ultrasonic exploration of the femoral neck is of wide interest as it can provide some information about a potential fracture risk, particularly for osteoporosic patients. In vivo, the ultrasonic wave first propagates through soft tissues that can be idealized as a homogeneous fluid. Then, the ultrasonic wave interacts with the bone structure. Transmitted and back-propagated signals are then measured at receivers. A numerical model of this complete chain is useful to understand and control the various parameters involved in this process. The complexity of the bone structure is approached using the elastodynamic finite difference time domain (FDTD) code SimSonic. Due to the small size of the spatial grid needed by FDTD schemes, the propagation between the emitter and the femoral neck may be excessively time and resource consuming. We have developed a coupling between SimSonic and a direct and fast evaluation of the diffraction in homogeneous fluids, based on the numerical discretization of the Rayleigh integral. This approach allows to reduce drastically the total computation time for the complete simulation. Results obtained with this new system are presented, including computation times and computer resources. This approach is particularly useful to simulate experiments with phased arrays, which involve several emissions.