Noninvasive Transcranial Ultrasound System

Abstract

Conventional ultrasound (US) is essentially ineffective transmitting acoustic frequencies necessary for high resolution brain imaging through the adult skull due the large acoustic impedance that exists at the skull-brain interface. Here, we present a proof-of-concept system that uses pulsed microwave (RF) energy that transmits through the skull bone and generates US waves via thermoelastic expansion in brain tissue. The RF emitter is a multi-element phased array placed outside the skull that can steer and focus US waves within the brain interior. We have demonstrated that a hand-scale RF array can noninvasively generate US waves ranging in frequency from 20 kHz - 1 MHz within a skull/brain phantom. In this demonstration, US waves are measured with a contact transducer via a port through the phantom skull. However, for a total noninvasive system, we propose the use of coherent whose optical wavelength has the potential to penetrate bone. The light carrier would be modulated by the US vibration within brain tissue which then transmits back to the device positioned outside the skull, thus, acting as a noninvasive US receiver. This RFUS system is being developed with the goal of producing a portable point-of-care intracranial hemorrhage (ICH) detection system. We are also exploring the potential of RFUS to perform quantitative elastography characterizing the stages of hematoma progression and as a therapy activating neuromodulation to modify brain function.