Numerical modeling of high‐intensity focused ultrasound for hemostatic applications

A promising therapeutic application of high‐intensity focused ultrasound (HIFU) is hemostasis. In one possible hemostatic application, ultrasound induced heating will be used to stop bleeding during open surgery. To achieve substantial heat deposition on the surface of the bleeding organ, intense acoustic fields will be used, and therefore nonlinear effects on wave propagation in the coupling liquid between the transducer and the treated region must be taken into account. Moreover, nonlinearity can be used to increase the efficiency of heat deposition in shallow tissues by transforming wave energy to higher harmonics. Theoretical characterization of acoustic field is performed using a one‐dimensional spherical wave model and the KZK equation. On‐axis and off‐axis waveforms, spatial distributions of harmonics, acoustic intensity, and heat deposition are calculated numerically in water and in tissue using a frequency‐domain scheme. The influence of operating frequency, initial intensity, transducer aperture, amplitude shading, focal depth, and position of the water–tissue interface on acoustic propagation regimes and associated tissue heating is studied. For given absorption properties of the tissue and desirable spatial shape of the thermal lesion, an optimal set of transducer parameters and corresponding nonlinear effects are presented and discussed. [Work supported by DARPA, ONR, CRDF and RFBR.]