Dual mode CMUT Array Operation for Skull Imaging and Passive Acoustic Monitoring in Transcranial Ultrasound

Transcranial focused ultrasound (tFUS) therapy shows great potential in several applications, including blood brain barrier (BBB) opening. In these applications two important aspects are the registration of the skull to CT images for aberration correction and monitoring the microbubble (MB) activity using methods like passive acoustic mapping (PAM). Currently the image registration is performed using MRI as the tFUS ultrasound arrays with piezoelectric transducers are not optimized as wideband transducers for higher resolution imaging rather they are tuned to MB excitation and detection frequencies. The potential of capacitive micromachined ultrasonic transducer (CMUT) as wideband and low noise receiver for tFUS has been already realized. However, CMUT has some unique characteristics such as control of operation mode which in turn can change its frequency in a very broad range, from MB excitation, to detection and skull imaging for image registration. In this work, we demonstrate the feasibility of multi-mode operation of CMUT operation for tFUS, where the same commercially available CMUT is used for both MB activity monitoring for PAM as well as skull imaging. Furthermore, experiments show that the same array can potentially be used for both MB activity excitation/detection in addition to skull imaging. This is achieved by using the same CMUT in conventional and collapsed mode effectively utilizing a frequency range of 0.5 MHz to 5 MHz.