Simulation aided dosing control of a 2D array therapeutic ultrasound transducer

Setting proper input power and duty cycle to produce a desired thermal dose is a non-trivial task in ultrasound thermal therapy. This paper presents an approach to estimate these parameters based on computer simulations. An in-house custom 2D therapeutic phased array was used for the studies. Acoustic power measurements were used to provide input values and validation for the pressure and temperature field simulations. Simulated pressure, intensity and temperature fields were in turn used to optimize the dosing control parameters. Simulation-projected dosing parameters were verified in a gellum-gum based tissue mimicking phantom (TMM) with 75μm butt-welded thermocouples (TC) embedded inside. The time averaged input powers were varied from 12W to 25W. A 30s dose was applied at each setting, and the temperatures at the focus and a location 2mm away from the focus in array azimuth direction were acquired. Results showed that the peak end-of-dose temperature rise was approximately linearly proportional to the input acoustic power. Simulations predicted a similar linear relationship with less than 10% error from the experimental results. Ex-vivo bovine liver studies also showed good correlation between the simulation-predicted lesion and the experimental lesion; similar patterns were observed. The results demonstrated that by combining simulations with force balance measurement, dosing instructions for any desired focal temperature can be quickly and easily produced.