A Systematic Investigation of Thermal Effects of High-Intensity Focused Ultrasound Therapy for Ultrasound Neuromodulation

Ultrasound neuromodulation has demonstrated potentials for noninvasively activating ion channels within cell membranes and regulating neuronal activities in animal models and humans. The thermal effects of focused ultrasound (FUS) play a significant role in activating the thermosensitive ion channels. However, until now, the effects of various FUS parameters on the resultant temperature distribution for activating thermosensitive ion channels have not yet been sufficiently elucidated. In this study, in vitro experiments are conducted by using high-intensity FUS transducers in three different types of porcine tissues, including pork, liver, and brain tissues. The influences of different ultrasound parameters on thermal effects are systematically analyzed. Our results show that elevating the ultrasound parameters, including ultrasound frequency, acoustic power, and duty cycle, can directly increase temperature rising rates and peak temperature values, while varying the pulse cycle number from 10 to 20 has nearly no impact. Furthermore, higher frequency ultrasound stimulation, such as 1.59 and 2 MHz, exhibits a larger temperature difference in the vicinity of the focal region. Our results also reveal that the temperature rising rate varies in that three types of tissues, which is dominant by the distinct acoustic attenuation coefficients. The findings in this study provide valuable insights for designing an effective ultrasound thermal neuromodulation sequence for clinical applications.