Ultrasound Waveform Optimization for Power Efficient Focused Ultrasound Neuromodulation

Tese de mestrado, Engenharia Biomédica e Biofísica, 2023, Universidade de Lisboa, Faculdade de CiênciasUltrasound neuromodulation is a promising ultrasound modality since it combines high spatial resolution and high coverage of the brain while remaining minimally invasive. It is performed by exciting a transducer with an alternating pulse signal at its resonance frequency. These pulse signals are typically sent in bursts. The piezoelectric transducer converts this signal into an acoustic wave, resulting in multiple acoustic waves within each burst. Bulk ceramic piezoelectric transducers have a high-quality factor, meaning that for a single pulse excitation, it produces several pulses with decaying amplitude. The main goal of this dissertation was to explore potential power savings in the ultrasound transmitter by removing pulses from a long burst of pulses and bursts from the neuromodulation cycle while minimizing the decay of the acoustic wave amplitude. This goal was accomplished by developing an experimental setup for ultrasound stimulation using two different transducers: High-Intensity Focused Ultrasound and Air-Backing transducers. In this study, it was also simulated two different approaches: removing pulses by short and open circuits. The results showed that using the Air-Backing transducer, it’s possible to save more energy than with the other transducer. The simulations from the Air-Backing transducer, in which only a percentage of the pulse amplitude was removed, showed better results than the total removal of the pulses, and among the results presented, the 30% amplitude removal is the case with the highest efficiency. Another comparison made in this project suggests that performing pulse removal through a short circuit generates very positive results while performing pulse removal through an open circuit was not beneficial to the hypothesis under study. Future work to be done should include experiments and simulations with neurons since the behavior of ultrasound in neurons is still not fully understood, and the obtained results may prove to be quite different from the simulations