Preliminary investigation of dual mode CMUT probe for ultrasound image guided HIFU therapy

This preliminary study focuses on Capacitive Micro-machined Ultrasound Transducers (CMUTs) for dualmode ultrasound therapy and imaging. A planar probe design is being investigated in the context of Ultrasound-guided High Intensity Focused Ultrasound (USgHIFU) designed for endocavitary HIFU tissue ablation of the prostate gland. The hypothesis is that this CMUT design could offer potential advantages over currently used piezoelectric probes such as ease of miniaturization, increased elements for improved imaging and more control over electronic focusing allowing focal therapy. A planar dual mode CMUT probe consisting of a 3 MHz, 64-element annular array for therapy and 7 MHz, 256-element linear array for imaging were investigated in simulation and experimentally. Numerical models of the pressure field and tissue heating simulations were performed and compared with an existing piezo-based geometrically focused annular array HIFU probe (16 rings) with a hole in the center that possesses a curvilinear imaging array (128 elements). To validate the modelling and the focusing capabilities, pressure field hydrophone measurements were performed. Simulations showed that the planar annular CMUT design could dynamically focus from 3-7cm which matched well with the experimentally obtained pressure field data. Radiation force balance measurements confirmed the desired 5 W/cm
²
surface acoustic intensity. This CMUT prototype will require further investigation for determination of the robustness of this technology and the ability to create lesions, yet according to the modelling and experimental validation thus far, this CMUT design shows promise for improved USgHIFU treatment strategies.