Evaluation of capacitive micromachined ultrasonic transducers for passive monitoring of microbubble-assisted ultrasound therapies.

Passive cavitation detection can be performed to monitor microbubble activity during brain therapy. Microbubbles under ultrasound exposure generate a response characterized by multiple nonlinear emissions. Here, the wide bandwidth of capacitive micromachined ultrasonic transducers (CMUTs) was exploited to monitor the microbubble signature through a rat skull and a macaque skull. The intrinsic nonlinearity of the CMUTs was characterized in receive mode. Indeed, undesirable nonlinear components generated by the CMUTs must be minimized as they can mask the microbubble harmonic response. The microbubble signature at harmonic and ultra-harmonic components (0.5-6 MHz) was successfully extracted through a rat skull using moderate bias voltage.