A retrospective qualitative report of symptoms and safety from transcranial focused ultrasound for neuromodulation in humans

Abstract

Low intensity transcranial focused ultrasound (LifU) is a promising method of non-invasive neuromodulation that uses mechanical energy to affect neuronal excitability. LIFU confers high spatial resolution and adjustable focal lengths for precise neuromodulation of discrete regions in the human brain. Before the full potential of low intensity ultrasound for research and clinical application can be investigated, data on the safety of this technique is indicated. Here, we provide an evaluation of the safety of LifU for human neuromodulation through participant report and neurological assessment with a comparison of symptomology to other forms of non-invasive brain stimulation. participants (n = 120) that were enrolled in one of seven human ultrasound neuromodulation studies in one laboratory at the University of Minnesota (2015-2017) were queried to complete a follow-up Participant Report of Symptoms questionnaire assessing their self-reported experience and tolerance to participation in LifU research (i sppa 11.56-17.12 W/cm 2) and the perceived relation of symptoms to LIFU. A total of 64/120 participant (53%) responded to follow-up requests to complete the Participant Report of Symptoms questionnaire. None of the participants experienced serious adverse effects. From the post-hoc assessment of safety using the questionnaire, 7/64 reported mild to moderate symptoms, that were perceived as 'possibly' or 'probably' related to participation in LIFU experiments. These reports included neck pain, problems with attention, muscle twitches and anxiety. The most common unrelated symptoms included sleepiness and neck pain. There were initial transient reports of mild neck pain, scalp tingling and headache that were extinguished upon follow-up. No new symptoms were reported upon follow up out to 1 month. The profile and incidence of symptoms looks to be similar to other forms of non-invasive brain stimulation. Transcranial focused ultrasound (LIFU) is a new and promising non-surgical low-energy technique that uses mechanical energy to modulate neuronal activity with high spatial resolution and adjustable depth of focus. LIFU has been used safely and effectively for cortical and sub-cortical neuromodulation in mouse 1-4 , rat 5-7 , rabbit 8 , sheep 9,10 , pig 11 and primate 12-15 , and has also been demonstrated to be an effective method of transient cortical and sub-cortical neuromodulation in humans 16,17. In humans, LIFU has been applied to the temporal cortex 18 , primary somatosensory cortex (S1) 16,19 , secondary somatosensory cortex (S2) 20 , primary motor cortex 21 , primary visual cortex 22 and thalamus 17,23. LIFU has been shown to affect the amplitude of evoked potentials 8,16,19 , the power, phase and frequency of the electroencephalogram (EEG) 16,24 ; the blood oxygen level dependent (BOLD) magnetic resonance imaging signal 8,25,26 , as well as tactile 16,19 and reaction time 21 behavior. As currently employed, human neuromodulation with LIFU typically involves coupling one (or more than one 20) focused single-el...

Systematic examination of low-intensity ultrasound parameters on human motor cortex excitability and behavior

“…(Mueller et al, 2016). Though no human studies have reported any permanent adverse effects from application of low-intensity TUS (Legon et al, 2020), a single sheep study showed small microhemorrhages at the cortical site of sonication, albeit after prolonged repetitive (>500) trials at intensities (I SPPA = 10.5 W/cm 2 ) higher than used in our study (Gaur et al, 2020;Lee et al, 2016c). The absence of edema, necrosis, or local inflammatory responses, as well as a lack of control group may implicate post-mortem brain extraction as the cause of these findings, rather than sonication itself.…”

Transcranial Ultrasound Innovations Ready for Broad Clinical Application

“…Following these, a third recent report assembled data from 64 subjects over 7 experiments. [53] Events were classified as possibly/probably related and unlikely/unrelated to ultrasound stimulation. For the first class, neck pain, difficulty paying attention, muscles twitches and anxiety were described (7/64).…”

“…[Correction added after publication on 02 December 2020: In the last paragraph of Section 5, the missing reference, [53], was added. ]…”

Transcranial Focused Ultrasound Neuromodulation of Voluntary Movement-related Cortical Activity in Humans

“…Although our study administered less ultrasound intensities than those 450 applied in (Legon et al, 2020) and even much less than the FDA's guideline 451 (ISPPA ≤ 190 W/cm 2 ) (FDA, 2008), we were also cautious about the tFUS 452 safety on the subjects during the experiment sessions. We surveyed the 453 subjects with a brief questionnaire for report of symptoms, such as headache, 454 neck pain, dental pain, nausea, dizziness, anxiety, abnormal muscle 455 contractions etc., before and after tFUS sessions.…”

“…Low intensity tFUS neuromodulation is deemed as generally safe without 447 inducing serious adverse effects on humans upon careful control of the 448 ultrasound intensities (ISPPA: 11.56-17.12 W/cm 2 ) (Legon et al, 2020).…”