A High Sensitivity CMUT-Based Passive Cavitation Detector for Monitoring Microbubble Dynamics During Focused Ultrasound Interventions.

Abstract

Tracking and controlling microbubble (MB) dynamics in the human brain through acoustic emission monitoring during transcranial focused ultrasound therapy (tFUS) is critical for attaining safe and effective treatments. The low-amplitude MB emissions have harmonic and ultra-harmonic components, necessitating a broad bandwidth and low-noise system for monitoring transcranial MB activity. Capacitive Micromachined Ultrasonic Transducers (CMUTs) offer high sensitivity and low noise over a broad bandwidth, especially when they are tightly integrated with electronics, making them a good candidate technology for monitoring the MB activity through human skull. In this study, we designed a 16-channel Analog Front-end Electronics (AFE) with a low-noise transimpedance amplifier (TIA), a band-gap reference circuit, and an output buffer stage. To assess AFE performance and ability to detect MB acoustic emission, we combined it with a commercial CMUT array. The integrated system has 12.3 - 61.25 mV/Pa receive sensitivity with 0.085 - 0.23 mPa/ √ Hz minimum detectable pressure up to 3 MHz for a single element CMUT with 3.78 mm2 area. Experiments with free microbubbles in a microfluidic channel demonstrate that our system is able to capture key spectral components of MBs' harmonics when sonicated at clinically relevant frequencies (0.5 MHz) and pressures (250 kPa). Together our results demonstrate that the proposed CMUT system can support the development of novel passive cavitation detectors to track MB activity for attaining safe and effective FUS treatments.