Histologic safety of transcranial focused ultrasound neuromodulation and magnetic resonance acoustic radiation force imaging in rhesus macaques and sheep

Abstract

Background: Neuromodulation by transcranial focused ultrasound (FUS) offers the potential to non-invasively treat specific brain regions, with treatment location verified by magnetic resonance acoustic radiation force imaging (MR-ARFI).Objective: To investigate the safety of these methods prior to widespread clinical use, we report histologic findings in two large animal models following FUS neuromodulation and MR-ARFI.Methods: Two rhesus macaques and thirteen Dorset sheep were studied. FUS neuromodulation was targeted to the primary visual cortex in rhesus macaques and to subcortical locations, verified by MR-ARFI, in eleven sheep. Both rhesus macaques and five sheep received a single FUS session, whereas six sheep received repeated sessions three to six days apart. The remaining two control sheep did not receive ultrasound but otherwise underwent the same anesthetic and MRI procedures as the eleven experimental sheep.Hematoxylin and eosin-stained sections of brain tissue (harvested zero to eleven days fol- * Corresponding Author: lowing FUS) were evaluated for tissue damage at FUS and control locations as well as tissue within the path of the FUS beam. TUNEL staining was used to evaluate for the presence of apoptosis in sheep receiving high dose FUS.Results: No FUS-related pre-mortem histologic findings were observed in the rhesus macaques or in any of the examined sheep. Extravascular red blood cells (RBCs) were present within the meninges of all sheep, regardless of treatment group. Similarly, small aggregates of perivascular RBCs were rarely noted in non-target regions of neural parenchyma of FUS-treated (8/11) and untreated (2/2) sheep. However, no concurrent histologic abnormalities were observed, consistent with RBC extravasation occurring as post-mortem artifact following brain extraction. Sheep within the high dose FUS group were TUNELnegative at the targeted site of FUS. Conclusions:The absence of FUS-related histologic findings suggests that the neuromodulation and MR-ARFI protocols evaluated do not cause tissue damage.We evaluate histology in brain tissue following FUS neuromodulation in the visual 49 cortex of rhesus macaques, and following neuromodulation and MR-ARFI in subcortical 50 brain regions in sheep. The sheep histology includes a treatment control group in which 51 4 no FUS was applied, and internal controls from hemispheres not treated with FUS. Our 52 neuromodulation protocols included a component similar to those used in human stud-53 ies, and to those evaluated by Lee and colleagues. We also investigated a broader range 54 of intensity values and repeated number of FUS bursts, exceeding those values typically 55 used in human protocols as well as those used in the study by Lee et al. Our findings 56 provide important information for subsequent studies involving FUS neuromodulation or 57 MR-ARFI. 58 Materials and Methods 59 All animal experiments were performed with institutional approval from the Stanford 60 University Administrative Panel on Laboratory Animal Care. 61 Rhesus macaque s...

Ultrasound Neuromodulation Inhibits Seizures in Acute Epileptic Monkeys

“…In a study of 54 cases of ultrasound regulating the central nervous system, only two had ultrasound-related injuries (Blackmore et al, 2019). Another study on magnetic resonance acoustic radiation force imaging also pointed out that localized brain regions did not cause tissue damage after ultrasound stimulation (Gaur et al, 2020). Therefore, ultrasound may be a safe, noninvasive therapeutic method for the modulation of neurological disorders, including epilepsy and Parkinson's disease.…”

Low-Intensity Focused Ultrasound Neuromodulation for Stroke Recovery: A Novel Deep Brain Stimulation Approach for Neurorehabilitation?

“…103 Due to the biophysical properties of ultrasound and interaction of acoustic waves with tissue, the waves propagate through biological tissue with vibrational character creating acoustic radiation force (ARF). 96,104 Part of the energy is transmitted into mechanical deformation of the tissue and another part converted into thermal energy. 105 The main parameters used to calibrate ultrasound exposure are fundamental frequency, sonication intensity, pulse width, pulse repetition frequency, sonication duration and duty cycle (Figure 1).…”

“…75,78,84 Furthermore, increasing studies in smaller animals [85][86][87] , monkeys [88][89][90] , sheep 91 and first-in-humans studies 92 are highlighting the potential safety and feasibility of TUS as a novel NIBS method. 78,[93][94][95][96] However, as all relatively new techniques, TUS comes with a number of challenges that need to be addressed before being usable in large scale clinical practice for stroke recovery. In the present review we will discuss the discussed mechanisms underlying TUS neuromodulatory effects and highlight several promising applications of TUS for motor stroke recovery.…”