Influence of the Transducer Acoustic Power on Focal Location of the Beam

1 ABSTRACT The location of High Intensity Focused Ultrasound (HIFU) beam in a tissue medium is an important parameter in assessment of the thermal field as it influences the temperature rise in the tissue. Our hypothesis is that the location of the beam can be affected by the power of the transducer. HIFU procedure with 30s of sonication time was performed at different powers of transducer (5 to 60 W) as well as different initial locations of beam in a tissue mimicking material. Eight thermocouples were embedded at 4 different layers in a phantom to measure the temperature rise during HIFU procedure. An inverse method based on experimental data and optimization algorithm was used to find the actual location of beam based on the experimental data. Our experimental data showed that for a higher power (60 W) as compared to a lower power (5 W), the focal distance that the actual position of beam moves away from its initial location increased with the raise in power. Thus, beam location can change at different powers of transducer. Using inverse method we showed that there is a direct linear correlation (R = 0.95) between the transducer power and the distance that beam moves away from its initial location. Therefore, it is of great clinical importance to study the effects of transducer power on the location of HIFU beam in an attempt to minimize the damage to healthy cells.