Development of an Ultrasound Hyperthermia Simulator for Therapeutic Applications

In recent times, Ultrasound for therapeutic applications is becoming increasingly popular due to its high practicality and efficiency. However, determination of adequate dosages presents a great challenge due to the difficulty of measuring tissue temperatures during the process. Further, accurate calculation of temperature field induced by ultrasound within the tissue is difficult to develop because of the time-scale differences between pressure and temperature analyses. In order to overcome this issue, practical and accurate methods to couple both analyses are needed. In the present study, Westervelt’s nonlinear wave equation is used to simulate ultrasonic propagation driven by an unfocused piston source in an axisymmetric biological tissue phantom. Using the Finite Difference Time Domain (FDTD) method, a pressure field was calculated for different sinusoidal bursts, frequencies, and source pressures. Average heat generation fields were calculated from the pressure field within an adequate time range for practical purposes. The Pennes bioheat transfer equation with the calculated heat generation fields were used to acquire transient temperature distributions. Effect of source pressure, frequency, source radius, and trial duration on the temperature profiles was examined. It can be observed from the simulations that continuous wave signals increase temperature at a focus in shorter times, while discrete pulses with adequate duty factors can be useful in maintaining required temperatures constant while diffusing heat along the tissue. The methodology presented here can be of use in many applications such as increasing necrotic volume for tissue ablation purposes.