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 (AE) monitoring during transcranial focused ultrasound (tFUS) therapy are 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 (AFE) electronics 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 AE, we combined it with a commercial CMUT array. The integrated system has ${12}.{3}$ – ${61}.{25} ~\text {mV}/\text {Pa}$ receive sensitivity with ${0}.{085}$ – ${0}.{23}~\text {mPa}/\text {(}\text {Hz}\text {)}^{1/2}$ minimum detectable pressure (MDP) up to 3 MHz for a single element CMUT with 3.78 $\text {mm}^{{2}}$ area. Experiments with free MBs 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 (PCD) to track MB activity for attaining safe and effective focused ultrasound (FUS) treatments.