title: FDTD simulation of finite-amplitude pressure and temperature fields for biomedical ultrasound.
abstract: Full wave simulations provide a valuable tool for studying the spatial and temporal nature of an acoustic field. One method for producing such simulations is the finite-difference time-domain (FDTD) method. This method uses discrete differences to approximate derivatives in the governing partial differential equations. We used the FDTD method to model the propagation of finite-amplitude sound in a homogeneous thermoviscous fluid. The calculated acoustic pressure field was then used to compute the transient temperature rise in the fluid; the heating results from absorption of acoustic energy by the fluid. As an example, the transient temperature field was calculated in biological tissue in response to a pulse of focused ultrasound. Enhanced heating of the tissue from finite-amplitude effects was observed. The excess heating was attributed to the nonlinear generation of higher-frequency harmonics which are absorbed more readily than the fundamental. The effect of nonlinear distortion on temperature rise in tissue was observed to range from negligible at 1 MPa source pressure to an 80% increase in temperature elevation at 10 MPa source pressure.
authors.affiliation: Applied Physics Laboratory, University of Washington, Seattle 98105, USA. ibrahim@bwh.harvard.edu
authors.forename: I M
authors.initials: IM
authors.lastname: Hallaj
authors.forename: R O
authors.initials: RO
authors.lastname: Cleveland
mesh_terms: D000162:Acoustics; D006801:Humans; D008954:Models, Biological; D013814:Thermal Conductivity; D014465:Ultrasonics