A Piezoceramic Sensor for Detection of Focused Ultrasound-Induced Cavitation

Abstract

Acoustic cavitation plays a key role in blood-brain-barrier opening. Stable cavitation is required for safely transient barrier disruption when inertial cavitation may cause potentially undesirable damage to brain. To ensure the safety, an appropriate passive cavitation detector is needed to monitor cavitation activity during focused ultrasound treatment. The purpose of this study was to develop a passive cavitation detector with high sensitivity at the specific frequency used in blood-brain-barrier opening. The detector was designed with the assistance of pulse-echo response simulations, using the software PiezoCAD. The active transducer of the detector was constructed of two matching layers, a PZT-5A ceramic disk and the titanium backing. The detector was characterized via the pulse-echo measurements and a commercial hydrophone was used to determine the sensitivity of the developed detector. Cavitation experiments were also performed to validate the detector. The experimental results showed that the detector had the center frequency of 1.16 MHz with the bandwidth of 44.8% and its sensitivity was 2.87 V / MPa at 1.0 MHz. In cavitation experiments, 2-MHz focused ultrasound with the focal intensity of 58 W/cm(2) and 1461 W/cm(2) induced stable cavitation and inertial cavitation in free field, separately. The spectra of the ultrasound signals detected by the detector indicated the occurrence of peak voltages at the subharmonic frequency of 1 MHz and the increase in the level of wideband signals, reflecting stable cavitation and inertial cavitation, respectively. Based on the design guideline of this study, the passive cavitation detector can be developed dedicated for blood-brain-barrier opening.