Acoustical experimental design for ultrasonic neurostimulation on rodents

While the mechanisms of ultrasonic neurostimulation are still unknown, this method has been successfully shown on rodents from a variety of research groups. While the results are compelling, there has been limited work in characterizing the acoustic fields that are generated and ultimately delivered to the rodent brain which is important in order to determine the underlying neurostimulation mechanism. This presentation details some of the acoustical experimental design processes that are being undertaken at JHU/APL as well as our current progress in the rodent ultrasonic neurostimulation. The experimental design utilizes a complementary process of both simulation and experimentation verification to determine the expected delivered acoustic wave field. The simulation encompasses the full propagation path from the single element focused transducer, through an acoustic waveguide and skull, to the treatment location. This work uses a focused transducer with a center frequency of 0.5 MHz with several different waveguides that are characterized in our calibration tank with regards to intensity over space. Each of these waveguides is modeled and compared relative to the focal spot size and intensity delivered to the focal spot. These measurements are used to select an optimal waveguide which is used in the model to determine the expected performance of the full system. The presented results compare the performance of the waveguides and their impact on ultrasonic delivery to the rodent brain.