Acoustic cavitation sub-millisecond signal processing for ultrasound surgery

Cavitation in Focused Ultrasound Surgery (FUS) is a stochastic phenomenon that can evolve very rapidly at the high intensities typically employed. Cavitation activity can be monitored analyzing its acoustic signals in the frequency domain. Cavities act as strong scatterers of incident acoustic energy, potentially enhancing different therapeutic effects, e.g., thermal or mechanical, if properly controlled. We report on the development on an instrument capable of controlling acoustic cavitation at sub-millisecond speed. The cavitation noise signal has been recorded and processed by an FPGA coupled with a feedback loop, capable of modulating the driving field every few hundreds of microseconds to maintain an ideal level of cavitation activity and differentiate between several types of cavitation and the onset of boiling. The system has been tested in tissue phantom, ex-vivo tissue and in-vivo and the impact on lesion sizes has been analysed. We also used the experimental data as input for a non-linear simulation of the acoustic field specifically regarding the absorption/scatter ratio in the acoustic focus. [The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013/under REA grant agreement n° (623608).]