A 32-Channel Low-Intensity Focused Ultrasound Stimulator Using Phased Array Miniature Transducers for Enhanced Targeting Accuracy in Neuromuscular Rehabilitation System

Abstract

Low-intensity pulsed ultrasound (LIPUS) stimulation can be used for noninvasive neuromuscular rehabilitation. For increasing stimulation efficiency, focused ultrasound (FUS) providing high-energy concentration should be used for LIPUS stimulation. However, because of difficulties in fine focus control, it is difficult to accurately target a stimulation site with conventional FUS stimulators using a single transducer. For implementing highly accurate targeting with a finely adjustable focal point, a 32-channel low-intensity focused ultrasound (LIFU) stimulator using phased array miniature piezoelectric transducers is presented in this paper. In the presented stimulator, a beamforming technology is used to delicately control the focal point without the difficulties in the conventional FUS stimulators. The experimental results show that the focal point was successfully adjusted in horizontal and vertical directions with nearly zero targeting errors. The ultrasound energy with the spatial peak-pulse average intensity (I-sPPA) of 0.48 W/cm2 was concentrated in a focusing area of 1.05 mm radius, which is sufficiently small to target peripheral nerves or a bundle of muscle fibers.