Flexible Body-Conformal Ultrasound Patches for Image-Guided Neuromodulation

The paper presents the design and validation of body-conformal active ultrasound patches with integrated imaging and modulation modalities for image-guided neural therapy. A mechanically-flexible linear 64-element array of piezoelectric transducers with a resonance frequency of 5 MHz was designed for nerve localization. A second 8-element array using larger elements was integrated on the wearable probe for low intensity focused ultrasound neuromodulation at a resonance frequency of 1.3 MHz. Full-wave simulations were used to model the flexible arrays and estimate their generated pressure profiles. A focal depth of 10-20 mm was assumed for beamforming and focusing to support modulation of the vagus, tibial, and other nerves. A strain sensor integrated on the probe provides patient-specific feedback information on array curvature for real-time optimization of focusing and image processing. Each patch also includes high voltage (HV) multiplexers, transmit/receive switches, and pre-amplifiers that simplify connectivity and also improve the signal-to-noise ratio (SNR) of the received echo signals by $\sim$5 dB. Experimental results from a flexible prototype show a sensitivity of 80 kPa/V with $\sim$3 MHz bandwidth for the modulation and 20 kPa/V with $\sim$6 MHz bandwidth for the imaging array. An algorithm for accurate and automatic localization of targeted nerves based on using nearby blood vessels (e.g., the carotid artery) as image markers is also presented.