Research Project: Computational Techniques for Evaluating HIFU Safety and Effectiveness
Computational methods play an important in assessing the safety and effectiveness of HIFU devices. A user-friendly software package for simulation of pressure and intensity fields, temperature rise, and thermal dose distributions for HIFU transducers was developed and made available for general distribution. This is a frequency-domain code suitable for continuous beams.
A generalization of the standard model of ultrasound propagation and thermal heating was developed to account for changing absorption of tissue as it is cooked. Simulations predicted this change in absorption can have a very strong effect, resulting in peak temperatures as much as 70% higher than assuming static tissue properties as is often done in practice. Further, laboratory staff developed an analytic temperature-mode model for computing the temperature rise in tissue under conditions when nonlinear propagation generates significant higher harmonics, and they performed computations to define the threshold for when nonlinear models are required in acoustic propagation simulations. The outcome of this latter study will be useful in guiding manufacturers on when nonlinear (and typically more complicated and expensive to use) models are required and when linear models are adequate.
In collaboration with the University of Washington (UW), the time to boil for highly nonlinear ultrasound beams has been investigated using simulations and compared with experimental results. It has been shown that bandwidth limitations in the waveform measurements result in underestimation of heating rates; therefore a validated numerical model can be an effective tool in the laboratory and clinical settings. In a second UW collaboration, numerical simulations have been used to investigate the number of harmonics necessary to accurately estimate different quantities of interest, including peak positive and negative pressure, intensity, and heating rate.