title: Nonlinear derating of high-intensity focused ultrasound beams using Gaussian modal sums.
abstract: A method is introduced for using measurements made in water of the nonlinear acoustic pressure field produced by a high-intensity focused ultrasound transducer to compute the acoustic pressure and temperature rise in a tissue medium. The acoustic pressure harmonics generated by nonlinear propagation are represented as a sum of modes having a Gaussian functional dependence in the radial direction. While the method is derived in the context of Gaussian beams, final results are applicable to general transducer profiles. The focal acoustic pressure is obtained by solving an evolution equation in the axial variable. The nonlinear term in the evolution equation for tissue is modeled using modal amplitudes measured in water and suitably reduced using a combination of "source derating" (experiments in water performed at a lower source acoustic pressure than in tissue) and "endpoint derating" (amplitudes reduced at the target location). Numerical experiments showed that, with proper combinations of source derating and endpoint derating, direct simulations of acoustic pressure and temperature in tissue could be reproduced by derating within 5% error. Advantages of the derating approach presented include applicability over a wide range of gains, ease of computation (a single numerical quadrature is required), and readily obtained temperature estimates from the water measurements.
authors.affiliation: Mechanical Engineering Program, School of Dynamic Systems, University of Cincinnati, 2600 Clifton Avenue, Cincinnati, Ohio 45221.
authors.forename: Seyed Ahmad Reza
authors.initials: SA
authors.lastname: Dibaji
authors.forename: Rupak K
authors.initials: RK
authors.lastname: Banerjee
authors.forename: Joshua E
authors.initials: JE
authors.lastname: Soneson
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Myers
mesh_terms: D003198:Computer Simulation; D009038:Motion; D017711:Nonlinear Dynamics; D009716:Numerical Analysis, Computer-Assisted; D011312:Pressure; D013016:Sound; D013696:Temperature; D013997:Time Factors; D014160:Transducers, Pressure; D014465:Ultrasonics / Q000295:instrumentation / Q000379:methods*; D014867:Water
chemical_list: D014867:Water