Development of MR-compatible ultrasound brain stimulation system and monitoring of acoustic effects in mice

Abstract

Focused ultrasound stimulation (FUS) is a promising therapeutic modality for noninvasive targeted neuromodulation. Consequently, there is a growing need to investigate the direct neuronal effects of FUS using various imaging techniques. Functional magnetic resonance imaging (fMRI) is a well-established and mature technology that is theoretically compatible with FUS and is capable of whole-brain monitoring in real-time. However, existing ultrasonic stimulation systems are incompatible with high-resolution fMRI (> 7T) for small animals because commercially-available ultrasound transducers are generally bulky and cause external image artifacts under high magnetic field strength. This paper reports a miniaturized, MR-compatible ultrasound transducer system for simultaneous monitoring of FUS-induced acoustic effects using high resolution (9.4 T) fMRI in mice. Our system integrated (1) MR-compatible materials, (2) robust packaging and interface designs for ultrasound transmission, and (3) electromagnetic noise reduction techniques. Using this system, we demonstrate artifact-free echo-planar imaging (EPI) signal changes due to ultrasound brain stimulation in vivo. Our results provide a critical demonstration of miniaturized MR-compatible ultrasound stimulation systems for in vivo studies in small animals usinghigh-resolution functional imaging.