Abstract:

In low‐frequency transcranial ultrasound therapeutic applications, such as sonothrombolysis, standing waves have been identified as a potential source of undesirable collateral damage due to cavitation. Recently, a method for disrupting the standing wave pattern was developed by modulating the phase of the driving signal, producing a beam pattern with significantly lower ripple in pressure along the acoustic axis. Here we present a study conducted to determine the inertial cavitation threshold in tissue‐mimicking phantoms placed in a standing‐wave‐inducing chamber when the 272‐kHz focused therapy transducer was excited separately by a monochromatic or phase‐modulated continuous‐wave signal. A 10‐MHz receiver was used as a passive cavitation detector whose signal was digitally sampled to examine changes in the broadband signal amplitude. Results indicate that the pressure threshold for inertial cavitation is higher during random phase modulation, suggesting that such an approach would be suitable for transcranial ultrasound therapy. These results agree with a simulation of similar excitation signals on the bubble dynamics, which suggest that disruption of timing on bubble forcing reduces the explosive growth required to induce inertial cavitation. [Work supported by NIH Awards R25 CA089017‐06A2 and U41 RR19703.]