Focused Ultrasound-mediated Non-invasive Brain Stimulation: Examination of Sonication Parameters

Abstract

Background Transcranial focused ultrasound (FUS) has emerged as a new brain stimulation modality. The range of sonication parameters for successful brain stimulation warrants further investigation. Objective The objective of this study was to examine the range of FUS sonication parameters that minimize the acoustic intensity/energy deposition while successfully stimulating the motor brain area in Sprague-Dawley rats. Methods We transcranially administered FUS to the somatomotor area of the rat brain and measured the acoustic intensity that caused excitatory effects with respect to different pulsing parameters (tone-burst duration, pulse-repetition frequency, duty cycle, and sonication duration) at 350 and 650 kHz of fundamental frequency. Results We observed that motor responses were elicited at minimum threshold acoustic intensities (4.9–5.6 W/cm2 in spatial-peak pulse-average intensity; 2.5–2.8 W/cm2 in spatial-peak temporal-average intensity) in a limited range of sonication parameters, i.e. 1–5 ms of tone-burst duration, 50% of duty cycle, and 300 ms of sonication duration, at 350 kHz fundamental frequency. We also found that the pulsed sonication elicited motor responses at lower acoustic intensities than its equivalent continuous sonication. Conclusion Our results suggest that the pulsed application of FUS selectively stimulates specific brain areas-of-interest at an acoustic intensity that is compatible with regulatory safety limits on biological tissue, thus allowing for potential applications in neurotherapeutics.

Neuromodulation with transcranial focused ultrasound

“…Both the pulse duration and carrier frequency can be accommodated by current FDA guidelines—by using the time-average intensity and the mechanical index, respectively, as the limiting metrics. However, whether these exposure limits provide adequate guidelines for long-term neuromodulatory FUS—which appears to be capable of triggering plastic changes in neural circuits 26 —remains to be validated.…”

Suppression of EEG visual-evoked potentials in rats through neuromodulatory focused ultrasound

“…Subsequent animal studies were implemented to characterize the effects of different FUS parameters on inducing functional neuromodulation [8,9]. Specifically, a recent study by Kim et al [10] showed the existence of an optimal pulsing scheme that elicits excitatory neural activity.…”

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

“…The stimulator circuit controls the parameters required for pulsed sonication, such as acoustic intensity, fundamental frequency, pulse repetition frequency, duty cycle, sonication duration, and interstimulus interval. (25) In addition, the stimulator circuit calculates the time delays for each transducer element as a function of the location of the target focal point. According to the calculated results, 32 time-delayed highvoltage bipolar pulses are generated in the stimulator circuit.…”