Measurement-based simulation of temperature rise from focused and linear ultrasound fields and its validation with experiments

Accurate quantification of acoustic fields produced by biomedical ultrasound devices is essential for assessing thermal and mechanical bioeffects on the patient. Device characterization involves time-consuming measurements, which need to be performed under many operating conditions for complete risk evaluation. Also, there are difficulties in measuring high-intensity therapeutic fields, which can damage the measuring devices. In this study, measurement-based simulations of temperature rise induced by ultrasound absorption in a tissue mimicking material (TMM) under linear propagation conditions were undertaken. The objective was to demonstrate a methodology for quantifying the accuracy of measurement-based simulations (a case study) along with an assessment of the uncertainties associated with both experimental and simulation setups. The acoustic and thermal modelling was performed using a pseudospectral time-domain solver, k-Wave. (Note that the methodology is not specific to this solver.) Ultrasound heating was conducted in the TMM with source acoustic power levels ranging from 1.1 to 4.3 W for durations of 2 to 4 min. The peak temperature rises recorded at the acoustic focus from the embedded fine wire thermocouples ranged from 4.4 (0.6) to 16.4 (1.3) °C. The difference in simulated temperature rises across all heating conditions with respect to measurements ranged from –1.9% to 6.7%.