Repetitive pulsed-wave ultrasound stimulation suppresses neural activity by modulating ambient GABA levels via effects on astrocytes

Ultrasound is highly biopermeable and can non-invasively penetrate deep into the brain. Stimulation with patterned low-intensity ultrasound can induce sustained inhibition of neural activity in humans and animals, with potential implications for research and therapeutics. Although mechanosensitive channels are involved, the cellular and molecular mechanisms underlying neuromodulation by ultrasound remain unknown. To investigate the mechanism of action of ultrasound stimulation, we studied the effects of two types of patterned ultrasound on synaptic transmission and neural network activity using whole-cell recordings in primary cultured hippocampal cells. Single-shot pulsed-wave (PW) or continuous-wave (CW) ultrasound had no effect on neural activity. By contrast, although repetitive CW stimulation also had no effect, repetitive PW stimulation persistently reduced spontaneous recurrent burst firing. This inhibitory effect was dependent on extrasynaptic-but not synaptic-GABAA receptors, and the effect was abolished under astrocyte-free conditions. Pharmacological activation of astrocytic TRPA1 channels mimicked the effects of ultrasound by increasing the tonic GABAA current induced by ambient GABA. Pharmacological blockade of TRPA1 channels abolished the inhibitory effect of ultrasound. These findings suggest that the repetitive PW low-intensity ultrasound used in our study does not have a direct effect on neural function but instead exerts its sustained neuromodulatory effect through modulation of ambient GABA levels via channels with characteristics of TRPA1, which is expressed in astrocytes.

Nanobubble-actuated ultrasound neuromodulation for selectively shaping behavior in mice

Ultrasound is an acoustic wave which can noninvasively penetrate the skull to deep brain regions, enabling neuromodulation. However, conventional ultrasound's spatial resolution is diffraction-limited and low-precision. Here, we report acoustic nanobubble-mediated ultrasound stimulation capable of localizing ultrasound's effects to only the desired brain region in male mice. By varying the delivery site of nanobubbles, ultrasound could activate specific regions of the mouse motor cortex, evoking EMG signaling and limb movement, and could also, separately, activate one of two nearby deep brain regions to elicit distinct behaviors (freezing or rotation). Sonicated neurons displayed reversible, low-latency calcium responses and increased c-Fos expression in the sub-millimeter-scale region with nanobubbles present. Ultrasound stimulation of the relevant region also modified depression-like behavior in a mouse model. We also provide evidence of a role for mechanosensitive ion channels. Altogether, our treatment scheme allows spatially-targetable, repeatable and temporally-precise activation of deep brain circuits for neuromodulation without needing genetic modification.

Modulation of cardio-respiratory activity in mice via transcranial focused ultrasound

OBJECTIVE

The objective of this study was to investigate the effect of FUS on autonomic nervous system activity, including heart and respiratory rates, and to separate the thermal modulation from combined thermal and mechanical FUS effects.

METHODS

The thalamus and hypothalamus of wild-type mice were sonicated with a continuous-wave, 2 MHz FUS transducer at pressures of 425 and 850 kPa for 60 seconds. Cardiac and respiratory rates were monitored as signs of autonomic nervous activity. FUS-induced changes in autonomic activity were compared to FUS targeted to a spatially-distant motor region and to laser-induced heating.

RESULTS

FUS delivered to the primary target over the thalamus and hypothalamus at 850 kPa reversibly increased the respiratory rate by 6.5±3.2 breaths per minute and decreased the heart rate by 3.2±1.8 beats per minute. No significant changes occurred in this region at 425 kPa or when targeting the motor regions at 850 kPa. Laser heating with the same temperature rise profile produced by 850 kPa sonication resulted in cardiorespiratory modulation similar to that of FUS.

CONCLUSIONS

FUS is capable of reversibly and non-invasively modulating cardiorespiratory activity in mice. Localized changes in temperature may constitute the main cause for this activity, though further investigation is warranted into the distinct and complementary mechanisms of mechanically- and thermally-induced FUS neuromodulation. Close monitoring of vital signs during FUS neuromodulation may be warranted to monitor systemic responses to stimulation.

Acoustic hologram-induced virtual in vivo enhanced waveguide (AH-VIEW)

Optical imaging and phototherapy in deep tissues face notable challenges due to light scattering. We use encoded acoustic holograms to generate three-dimensional acoustic fields within the target medium, enabling instantaneous and robust modulation of the volumetric refractive index, thereby noninvasively controlling the trajectory of light. Through this approach, we achieved a remarkable 24.3% increase in tissue heating rate in vitro photothermal effect tests on porcine skin. In vivo photoacoustic imaging of mouse brain vasculature exhibits an improved signal-to-noise ratio through the intact scalp and skull. These findings demonstrate that our strategy can effectively suppress light scattering in complex biological tissues by inducing low-angle scattering, achieving an effective depth reaching the millimeter scale. The versatility of this strategy extends its potential applications to neuroscience, lithography, and additive manufacturing.

Genetically encoded mediators for sonogenetics and their applications in neuromodulation

Sonogenetics is an emerging approach that harnesses ultrasound for the manipulation of genetically modified cells. The great penetrability of ultrasound waves enables the non-invasive application of external stimuli to deep tissues, particularly advantageous for brain stimulation. Genetically encoded ultrasound mediators, a set of proteins that respond to ultrasound-induced bio-effects, play a critical role in determining the effectiveness and applications of sonogenetics. In this context, we will provide an overview of these ultrasound-responsive mediators, delve into the molecular mechanisms governing their response to ultrasound stimulation, and summarize their applications in neuromodulation.

Development and validation of a computational method to predict unintended auditory brainstem response during transcranial ultrasound neuromodulation in mice

BACKGROUND

Transcranial ultrasound stimulation (TUS) is a promising noninvasive neuromodulation modality. The inadvertent and unpredictable activation of the auditory system in response to TUS obfuscates the interpretation of non-auditory neuromodulatory responses.

OBJECTIVE

The objective was to develop and validate a computational metric to quantify the susceptibility to unintended auditory brainstem response (ABR) in mice premised on time frequency analyses of TUS signals and auditory sensitivity.

METHODS

Ultrasound pulses with varying amplitudes, pulse repetition frequencies (PRFs), envelope smoothing profiles, and sinusoidal modulation frequencies were selected. Each pulse's time-varying frequency spectrum was differentiated across time, weighted by the mouse hearing sensitivity, then summed across frequencies. The resulting time-varying function, computationally predicting the ABR, was validated against experimental ABR in mice during TUS with the corresponding pulse.

RESULTS

There was a significant correlation between experimental ABRs and the computational predictions for 19 TUS signals (R2 = 0.97).

CONCLUSIONS

To reduce ABR in mice during in vivo TUS studies, 1) reduce the amplitude of a rectangular continuous wave envelope, 2) increase the rise/fall times of a smoothed continuous wave envelope, and/or 3) change the PRF and/or duty cycle of a rectangular or sinusoidal pulsed wave to reduce the gap between pulses and increase the rise/fall time of the overall envelope. This metric can aid researchers performing in vivo mouse studies in selecting TUS signal parameters that minimize unintended ABR. The methods for developing this metric can be adapted to other animal models.

Higher harmonics dynamic focalization in single-element ring transducers using biaxial driving

Biaxial driving is a new driving technique that allows the steering of the ultrasound field generated by a single-element piezoceramic transducer. Because of their natural axisymmetric geometry, ultrasound generation with ring transducers can take advantage of the biaxial driving to change the focus of the beam generated by this type of transducer using only two driving signals. In this study, we applied the biaxial driving technique into a single-element PZT ring transducer operating at 500 kHz to produce a change in size and position of the focal spot while using the 1st (482 kHz), 3rd (1.362 MHz) and 5th (2.62 MHz) harmonic excitation. The transducer had a thickness of 2.85 mm, an inner diameter of 9.75 mm and a ring width of 2.0 mm, and two pairs of electrodes as required for biaxial driving. Simulation and experimental results showed that both the focal area and the distance at which the focal area centre was located changed as a function of the phase and power difference between the two driving signals. Experimental results showed that the focal area could be reduced from 31.6 mm² (conventional driving) to 3.4 mm² (89 % reduction) when using the first harmonic excitation. For the third harmonic, the focal area could be reduced from 4.0 mm² (conventional driving) to 3.3 mm² (17.5 % reduction). For the fifth harmonic, the focal area could be reduced from 1.7 mm² (conventional driving) to 1 mm² (41.7 % reduction). Results also demonstrated the centre of the focus could be displaced between 3.0 mm and 9.3 mm from the surface of the transducer when using the first harmonic, between 7.3 mm and 8.4 mm at the third harmonic, and between 4.9 mm and 8.2 mm at the fifth harmonic. The reduction in the focus area, as well as the possibility to displace the focus dynamically will be advantageous for preclinical applications of focused ultrasound, especially on drug delivery and neuromodulation studies in small rodents.

Effect of low-intensity transcranial ultrasound stimulation on theta and gamma oscillations in the mouse hippocampal CA1

Previous studies have demonstrated that low-intensity transcranial ultrasound stimulation (TUS) can eliminate hippocampal neural activity. However, until now, it has remained unclear how ultrasound modulates theta and gamma oscillations in the hippocampus under different behavioral states. In this study, we used ultrasound to stimulate the CA1 in mice in anesthesia, awake and running states, and we simultaneously recorded the local field potential of the stimulation location. We analyzed the power spectrum, phase-amplitude coupling (PAC) of theta and gamma oscillations, and their relationship with ultrasound intensity. The results showed that (i) TUS significantly enhanced the absolute power of theta and gamma oscillations under anesthesia and in the awake state. (ii) The PAC strength between theta and gamma oscillations is significantly enhanced under the anesthesia and awake states but is weakened under the running state with TUS. (iii) Under anesthesia, the relative power of theta decreases and that of gamma increases as ultrasound intensity increases, and the result under the awake state is opposite that under the anesthesia state. (iv) The PAC index between theta and gamma increases as ultrasound intensity increases under the anesthesia and awake states. The above results demonstrate that TUS can modulate theta and gamma oscillations in the CA1 and that the modulation effect depends on behavioral states. Our study provides guidance for the application of ultrasound in modulating hippocampal function.

Multifocal skull-compensated transcranial focused ultrasound system for neuromodulation applications based on acoustic holography

Transcranial focused ultrasound stimulation is a promising therapeutic modality for human brain disorders because of its noninvasiveness, long penetration depth, and versatile spatial control capability through beamforming and beam steering. However, the skull presents a major hurdle for successful applications of ultrasound stimulation. Specifically, skull-induced focal aberration limits the capability for accurate and versatile targeting of brain subregions. In addition, there lacks a fully functional preclinical neuromodulation system suitable to conduct behavioral studies. Here, we report a miniature ultrasound system for neuromodulation applications that is capable of highly accurate multiregion targeting based on acoustic holography. Our work includes the design and implementation of an acoustic lens for targeting brain regions with compensation for skull aberration through time-reversal recording and a phase conjugation mirror. Moreover, we utilize MEMS and 3D-printing technology to implement a 0.75-g lightweight neuromodulation system and present in vivo characterization of the packaged system in freely moving mice. This preclinical system is capable of accurately targeting the desired individual or multitude of brain regions, which will enable versatile and explorative behavior studies using ultrasound neuromodulation to facilitate widespread clinical adoption.

An Inverse Class-E Power Amplifier for Ultrasound Transducer

An inverse Class-E power amplifier was designed for an ultrasound transducer. The proposed inverse Class-E power amplifier can be useful because of the low series inductance values used in the output matching network that helps to reduce signal distortions. Therefore, a newly designed Class-E power amplifier can obtain a proper echo signal quality. The measured output voltage, voltage gain, voltage gain difference, and power efficiency were 50.1 V, 22.871 dB, 0.932 dB, and 55.342%, respectively. This low voltage difference and relatively high efficiency could verify the capability of the ultrasound transducer. The pulse-echo response experiment using an ultrasound transducer was performed to verify the capability of the proposed inverse Class-E power amplifier. The obtained echo signal amplitude and pulse width were 6.01 mV_p-p and 0.81 μs, respectively. The -6 dB bandwidth and center frequencies of the echo signal were 27.25 and 9.82 MHz, respectively. Consequently, the designed Class-E power amplifier did not significantly alter the performance of the center frequency of the ultrasound transducer; therefore, it could be employed particularly in certain ultrasound applications that require high linearity and reasonable power efficiency.

Advances in applications of head mounted devices (HMDs): Physical techniques for drug delivery and neuromodulation

Head-mounted medical devices (HMDs) are disruptive inventions representing laboratories and clinical institutions worldwide are climbing the apexes of brain science. These complex devices are inextricably linked with a wide range knowledge containing the Physics, Imaging, Biomedical engineering, Biology and Pharmacology, particularly could be specifically designed for individuals, and finally exerting integrated bio-effect. The salient characteristics of them are non-invasive intervening in human brain's physiological structures, and alterating the biological process, such as thermal ablating the tumor, opening the BBB to deliver drugs and neuromodulating to enhance cognitive performance or manipulate prosthetic. The increasing demand and universally accepted of them have set off a dramatic upsurge in HMDs' studies, seminal applications of them span from clinical use to psychiatric disorders and neurological modulation. With subsequent pre-clinical studies and human trials emerging, the mechanisms of transcranial stimulation methods of them were widely studied, and could be basically came down to three notable approach: magnetic, electrical and ultrasonic stimulation. This review provides a comprehensive overviews of their stimulating mechanisms, and recent advances in clinic and military. We described the potential impact of HMDs on brain science, and current challenges to extensively adopt them as promising alternative treating tools.

Simultaneous multi-target ultrasound neuromodulation in freely-moving mice based on a single-element ultrasound transducer

Objective.Ultrasound neuromodulation has become an emerging method for the therapy of neurodegenerative and psychiatric diseases. The phased array ultrasonic transducer enables multi-target ultrasound neuromodulation in small animals, but the relatively large size and mass and the thick cables of the array limit the free movement of small animals. Furthermore, spatial interference may occur during multi-target ultrasound brain stimulation with multiple micro transducers.Approach.In this study, we developed a miniature power ultrasound transducer and used the virtual source time inversion method and 3D printing technology to design, optimize, and manufacture the acoustic holographic lens to construct a multi-target ultrasound neuromodulation system for free-moving mice. The feasibility of the system was verified byin vitrotranscranial ultrasound field measurements,in vivodual-target blood-brain barrier (BBB) opening experiments, andin vivodual-target ultrasound neuromodulation experiments.Main results.The developed miniature transducer had a diameter of 4.0 mm, a center frequency of 1.1 MHz, and a weight of 1.25 g. The developed miniature acoustic holographic lens had a weight of 0.019 g to generate dual-focus transcranial ultrasound. The ultrasonic field measurements' results showed that the bifocal's horizontal distance was 3.0 mm, the -6 dB focal spot width in thex-direction was 2.5 and 2.25 mm, and 2.12 and 2.24 mm in they-direction. Finally, thein vivoexperimental results showed that the system could achieve dual-target BBB opening and ultrasound neuromodulation in freely-moving mice.Significance.The ultrasonic neuromodulation system based on a miniature single-element transducer and the miniature acoustic holographic lens could achieve dual-target neuromodulation in awake small animals, which is expected to be applied to the research of non-invasive dual-target ultrasonic treatment of brain diseases in awake small animals.

General-Purpose Ultrasound Neuromodulation System for Chronic, Closed-Loop Preclinical Studies in Freely Behaving Rodents

Transcranial focused ultrasound stimulation (tFUS) is an effective noninvasive treatment modality for brain disorders with high clinical potential. However, the therapeutic effects of ultrasound neuromodulation are not widely explored due to limitations in preclinical systems. The current preclinical studies are head-fixed, anesthesia-dependent, and acute, limiting clinical translatability. Here, this work reports a general-purpose ultrasound neuromodulation system for chronic, closed-loop preclinical studies in freely behaving rodents. This work uses microelectromechanical systems (MEMS) technology to design and fabricate a small and lightweight transducer capable of artifact-free stimulation and simultaneous neural recording. Using the general-purpose system, it can be observed that state-dependent ultrasound neuromodulation of the prefrontal cortex increases rapid eye movement (REM) sleep and protects spatial working memory to REM sleep deprivation. The system will allow explorative studies in brain disease therapeutics and neuromodulation using ultrasound stimulation for widespread clinical adoption.

High-precision neural stimulation by a highly efficient candle soot fiber optoacoustic emitter

Highly precise neuromodulation with a high efficacy poses great importance in neuroscience. Here we developed a candle soot fiber optoacoustic emitter (CSFOE), capable of generating a high pressure of over 10 MPa with a central frequency of 12.8 MHz, enabling highly efficient neuromodulation in vitro. The design of the fiber optoacoustic emitter, including the choice of the material and the thickness of the layered structure, was optimized in both simulations and experiments. The optoacoustic conversion efficiency of the optimized CSFOE was found to be 10 times higher than the other carbon-based fiber optoacoustic emitters. Driven by a single laser, the CSFOE can perform dual-site optoacoustic activation of neurons, confirmed by calcium (Ca2+) imaging. Our work opens potential avenues for more complex and programmed control in neural circuits using a simple design for multisite neuromodulation in vivo.

The impact of low intensity ultrasound on cells: Underlying mechanisms and current status

Low intensity ultrasound (LIUS) has been adopted for a variety of therapeutic purposes because of its bioeffects such as thermal, mechanical, and cavitation effects. The mechanism of impact and cellular responses of LIUS in cellular regulations have been revealed, which helps to understand the role of LIUS in tumor treatment, stem cell therapy, and nervous system regulation. The review summarizes the bioeffects of LIUS at the cellular level and its related mechanisms, detailing the corresponding theoretical basis and latest research in the study of LIUS in the regulation of cells. In the future, the design of specific LIUS-mediated treatment strategies may benefit from promising investigations which is hoped to provide encouraging therapeutic data.

An Optimized Miniaturized Ultrasound Transducer for Transcranial Neuromodulation

Transcranial ultrasound stimulation (TUS) is a young neuromodulation technology, which uses ultrasound to achieve non-invasive stimulation or inhibition of deep intracranial brain regions, with the advantages of non-invasive, deep penetration, and high resolution. It is widely considered to be one of the most promising techniques for probing brain function and treating brain diseases. In preclinical studies, developing miniaturized transducers to facilitate neuromodulation in freely moving small animals is critical for understanding the mechanism and exploring potential applications. In this article, a miniaturized transducer with a half-concave structure is proposed. Based on the finite element simulation models established by PZFlex software, several ultrasound transducers with different concave curvatures were designed and analyzed. Based on the simulation results, half-concave focused ultrasonic transducers with curvature radii of 5 mm and 7.5 mm were fabricated. Additionally, the emission acoustic fields of the ultrasonic transducers with different structures were characterized at their thickness resonance frequencies of 1 MHz using a multifunctional ultrasonic test platform built in the laboratory. To verify the practical ability for neuromodulation, different ultrasound transducers were used to induce muscle activity in mice. As a result, the stimulation success rates were (32 ± 10)%, (65 ± 8)%, and (84 ± 7)%, respectively, by using flat, #7, and #5 transducers, which shows the simulation and experimental results have a good agreement and that the miniaturized half-concave transducer could effectively converge the acoustic energy and achieve precise and effective ultrasonic neuromodulation.

Laser Scanning Guided Localization Imaging with a Laser-Machined Two-Dimensional Flexible Ultrasonic Array

Advances in flexible integrated circuit technology and piezoelectric materials allow high-quality stretchable piezoelectric transducers to be built in a form that is easy to integrate with the body’s soft, curved, and time-dynamic surfaces. The resulting capabilities create new opportunities for studying disease states, monitoring health/wellness, building human–machine interfaces, and performing other operations. However, more widespread application scenarios are placing new demands on the high flexibility and small size of the array. This paper provides a 8 × 8 two-dimensional flexible ultrasonic array (2D-FUA) based on laser micromachining; a novel single-layer “island bridge” structure was used to design flexible array and piezoelectric array elements to improve the imaging capability on complex surfaces. The mechanical and acoustoelectric properties of the array are characterized, and a novel laser scanning and positioning method is introduced to solve the problem of array element displacement after deformation of the 2D-FUA. Finally, a multi-modal localization imaging experiment was carried out on the multi-target steel pin on the plane and curved surface based on the Verasonics system. The results show that the laser scanning method has the ability to assist the rapid imaging of flexible arrays on surfaces with complex shapes, and that 2D-FUA has wide application potential in medical-assisted localization imaging.

Low-Intensity Transcranial Ultrasound Stimulation: Mechanisms of Action and Rationale for Future Applications in Movement Disorders

Low-intensity transcranial ultrasound stimulation (TUS) is a novel non-invasive brain stimulation technique that uses acoustic energy to induce changes in neuronal activity. However, although low-intensity TUS is a promising neuromodulation tool, it has been poorly studied as compared to other methods, i.e., transcranial magnetic and electrical stimulation. In this article, we first focus on experimental studies in animals and humans aimed at explaining its mechanisms of action. We then highlight possible applications of TUS in movement disorders, particularly in patients with parkinsonism, dystonia, and tremor. Finally, we highlight the knowledge gaps and possible limitations that currently limit potential TUS applications in movement disorders. Clarifying the potential role of TUS in movement disorders may further promote studies with therapeutic perspectives in this field.

Microscale concert hall acoustics to produce uniform ultrasound stimulation for targeted sonogenetics in hsTRPA1-transfected cells

The field of ultrasound neuromodulation has rapidly developed over the past decade, a consequence of the discovery of strain-sensitive structures in the membrane and organelles of cells extending into the brain, heart, and other organs. Notably, clinical trials are underway for treating epilepsy using focused ultrasound to elicit an organized local electrical response. A key limitation to this approach is the formation of standing waves within the skull. In standing acoustic waves, the maximum ultrasound intensity spatially varies from near zero to double the mean in one half a wavelength, and has lead to localized tissue damage and disruption of normal brain function while attempting to evoke a broader response. This phenomenon also produces a large spatial variation in the actual ultrasound exposure in tissue, leading to heterogeneous results and challenges with interpreting these effects. One approach to overcome this limitation is presented herein: transducer-mounted diffusers that result in spatiotemporally incoherent ultrasound. Herein, we numerically and experimentally quantified the effect of a diffuser in an enclosed domain, and show that adding the diffuser leads to a two-fold increase in ultrasound responsiveness of hsTRPA1 transfected HEK cells. Furthermore, we demonstrate the diffuser allow us to produce an uniform spatial distribution of pressure in the rodent skull. Collectively, we propose that our approach leads to a means to deliver uniform ultrasound into irregular cavities for sonogenetics.

Current State of Potential Mechanisms Supporting Low Intensity Focused Ultrasound for Neuromodulation

Low intensity focused ultrasound (LIFU) has been gaining traction as a non-invasive neuromodulation technology due to its superior spatial specificity relative to transcranial electrical/magnetic stimulation. Despite a growing literature of LIFU-induced behavioral modifications, the mechanisms of action supporting LIFU's parameter-dependent excitatory and suppressive effects are not fully understood. This review provides a comprehensive introduction to the underlying mechanics of both acoustic energy and neuronal membranes, defining the primary variables for a subsequent review of the field's proposed mechanisms supporting LIFU's neuromodulatory effects. An exhaustive review of the empirical literature was also conducted and studies were grouped based on the sonication parameters used and behavioral effects observed, with the goal of linking empirical findings to the proposed theoretical mechanisms and evaluating which model best fits the existing data. A neuronal intramembrane cavitation excitation model, which accounts for differential effects as a function of cell-type, emerged as a possible explanation for the range of excitatory effects found in the literature. The suppressive and other findings need additional theoretical mechanisms and these theoretical mechanisms need to have established relationships to sonication parameters.

Transcranial Focused Ultrasound Stimulation of Periaqueductal Gray for Analgesia

OBJECTIVE

Transcranial focused ultrasound (tFUS) is regarded as a promising non-invasive stimulation tool for modulating brain circuits. The aim of this study is to explore the feasibility of tFUS stimulation for analgesia application.

METHODS

50 l of 3% formalin solution was injected into the rats left hindpaw to build a pain model, and then the local field potential (LFP) activities of the dorsal horn were tracked after a recording electrode was placed in the spinal cord. Rats were randomly divided into two groups: control group and tFUS group. At the 30th minute after formalin injection, tFUS (US-650 kHz, PD = 1 ms, PRF = 100 Hz, 691 mW/cm2) was conducted to stimulate the periaqueductal gray (PAG) for 5 minutes (on 5 s and off 5 s) in tFUS group, but there was no treatment in control group. In addition, the analgesia mechanism (LFP recording from the PAG) and safety assessment (histology analysis) were carried out.

RESULTS

The tFUS stimulation of the PAG can suppress effectively the nociceptive activity generated by formalin. The findings of the underlying mechanism exploration indicated that the tFUS stimulation was able to activate the PAG directly without causing significant temperature change and tissue injury.

CONCLUSION

The results illustrated that the tFUS stimulation of the PAG can achieve the effect of analgesia.

SIGNIFICANCE

This work provides new insights for the development of non-invasive analgesic technology in the future.

Review of Noninvasive or Minimally Invasive Deep Brain Stimulation

Brain stimulation is a critical technique in neuroscience research and clinical application. Traditional transcranial brain stimulation techniques, such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and deep brain stimulation (DBS) have been widely investigated in neuroscience for decades. However, TMS and tDCS have poor spatial resolution and penetration depth, and DBS requires electrode implantation in deep brain structures. These disadvantages have limited the clinical applications of these techniques. Owing to developments in science and technology, substantial advances in noninvasive and precise deep stimulation have been achieved by neuromodulation studies. Second-generation brain stimulation techniques that mainly rely on acoustic, electronic, optical, and magnetic signals, such as focused ultrasound, temporal interference, near-infrared optogenetic, and nanomaterial-enabled magnetic stimulation, offer great prospects for neuromodulation. This review summarized the mechanisms, development, applications, and strengths of these techniques and the prospects and challenges in their development. We believe that these second-generation brain stimulation techniques pave the way for brain disorder therapy.

32 Element Piezoelectric Micromachined Ultrasound Transducer (PMUT) Phased Array for Neuromodulation

Interest in utilizing ultrasound (US) transducers for non-invasive neuromodulation treatment, including for low intensity transcranial focused ultrasound stimulation (tFUS), has grown rapidly. The most widely demonstrated US transducers for tFUS are either bulk piezoelectric transducers or capacitive micromachine transducers (CMUT) which require high voltage excitation to operate. In order to advance the development of the US transducers towards small, portable devices for safe tFUS at large scale, a low voltage array of US transducers with beam focusing and steering capability is of interest. This work presents the design methodology, fabrication, and characterization of 32-element phased array piezoelectric micromachined ultrasound transducers (PMUT) using 1.5 μm thick Pb(Zr_0.52 Ti_0.48)O₃ films doped with 2 mol% Nb. The electrode/piezoelectric/electrode stack was deposited on a silicon on insulator (SOI) wafer with a 2 μm silicon device layer that serves as the passive elastic layer for bending-mode vibration. The fabricated 32-element PMUT has a central frequency at 1.4 MHz. Ultrasound beam focusing and steering (through beamforming) was demonstrated where the array was driven with 14.6 V square unipolar pulses. The PMUT generated a maximum peak-to-peak focused acoustic pressure output of 0.44 MPa at a focal distance of 20 mm with a 9.2 mm and 1 mm axial and lateral resolution, respectively. The maximum pressure is equivalent to a spatial-peak pulse-average intensity of 1.29 W/cm², which is suitable for tFUS application.

Design and Optimization of Ultrasound Phased Arrays for Large-Scale Ultrasound Neuromodulation

Low-intensity transcranial focused ultrasound stimulation (tFUS), as a noninvasive neuromodulation modality, has shown to be effective in animals and even humans with improved millimeter-scale spatial resolution compared to its noninvasive counterparts. But conventional tFUS systems are built with bulky single-element ultrasound (US) transducers that must be mechanically moved to change the stimulation target. To achieve large-scale ultrasound neuromodulation (USN) within a given tissue volume, a US transducer array should electronically be driven in a beamforming fashion (known as US phased array) to steer focused ultrasound beams towards different neural targets. This paper presents the theory and design methodology of US phased arrays for USN at a large scale. For a given tissue volume and sonication frequency (f), the optimal geometry of a US phased array is found with an iterative design procedure that maximizes a figure of merit (FoM) and minimizes side/grating lobes (avoiding off-target stimulation). The proposed FoM provides a balance between the power efficiency and spatial resolution of a US array in USN. A design example of a US phased array has been presented for USN in a rat's brain with an optimized linear US array. In measurements, the fabricated US phased array with 16 elements (16.7×7.7×2 mm³), driven by 150 V (peak-peak) pulses at f = 833.3 kHz, could generate a focused US beam with a lateral resolution of 1.6 mm and pressure output of 1.15 MPa at a focal distance of 12 mm. The capability of the US phased array in beam steering and focusing from -60^o to 60^o angles was also verified in measurements.

Precise Ultrasound Neuromodulation in a Deep Brain Region Using Nano Gas Vesicles as Actuators

Ultrasound is a promising new modality for non-invasive neuromodulation. Applied transcranially, it can be focused down to the millimeter or centimeter range. The ability to improve the treatment's spatial resolution to a targeted brain region could help to improve its effectiveness, depending upon the application. The present paper details a neurostimulation scheme using gas-filled nanostructures, gas vesicles (GVs), as actuators for improving the efficacy and precision of ultrasound stimuli. Sonicated primary neurons display dose-dependent, repeatable Ca²⁺ responses, closely synced to stimuli, and increased nuclear expression of the activation marker c-Fos in the presence of GVs. GV-mediated ultrasound triggered rapid and reversible Ca²⁺ responses in vivo and could selectively evoke neuronal activation in a deep-seated brain region. Further investigation indicate that mechanosensitive ion channels are important mediators of this effect. GVs themselves and the treatment scheme are also found not to induce significant cytotoxicity, apoptosis, or membrane poration in treated cells. Altogether, this study demonstrates a simple and effective method to achieve enhanced and better-targeted neurostimulation with non-invasive low-intensity ultrasound.

Transcranial Focused Ultrasound Neuromodulation: A Review of the Excitatory and Inhibitory Effects on Brain Activity in Human and Animals

Non-invasive neuromodulation technology is important for the treatment of brain diseases. The effects of focused ultrasound on neuronal activity have been investigated since the 1920s. Low intensity transcranial focused ultrasound (tFUS) can exert non-destructive mechanical pressure effects on cellular membranes and ion channels and has been shown to modulate the activity of peripheral nerves, spinal reflexes, the cortex, and even deep brain nuclei, such as the thalamus. It has obvious advantages in terms of security and spatial selectivity. This technology is considered to have broad application prospects in the treatment of neurodegenerative disorders and neuropsychiatric disorders. This review synthesizes animal and human research outcomes and offers an integrated description of the excitatory and inhibitory effects of tFUS in varying experimental and disease conditions.

A Wearable Ultrasonic Neurostimulator - Part I: A 1D CMUT Phased Array System for Chronic Implantation in Small Animals

In this work, we present a wireless ultrasonic neurostimulator, aiming at a truly wearable device for brain stimulation in small behaving animals. A 1D 5-MHz capacitive micromachined ultrasonic transducer (CMUT) array is adopted to implement a head-mounted stimulation device. A companion ASIC with integrated 16-channel high-voltage (60-V) pulsers was designed to drive the 16-element CMUT array. The ASIC can generate excitation signals with element-wise programmable phases and amplitudes: 1) programmable sixteen phase delays enable electrical beam focusing and steering, and 2) four scalable amplitude levels, implemented with a symmetric pulse-width-modulation technique, are sufficient to suppress unwanted sidelobes (apodization). The ASIC was fabricated in the TSMC 0.18- μm HV BCD process within a die size of 2.5 × 2.5 mm². To realize a completely wearable system, the system is partitioned into two parts for weight distribution: 1) a head unit (17 mg) with the CMUT array, 2) a backpack unit (19.7 g) that includes electronics such as the ASIC, a power management unit, a wireless module, and a battery. Hydrophone-based acoustic measurements were performed to demonstrate the focusing and beam steering capability of the proposed system. Also, we achieved a peak-to-peak pressure of 2.1 MPa, which corresponds to a spatial peak pulse average intensity ( I_SPPA) of 33.5 W/cm², with a lateral full width at half maximum (FWHM) of 0.6 mm at a depth of 3.5 mm.

Multielement Ring Array Based on Minute Size PMUTs for High Acoustic Pressure and Tunable Focus Depth

This paper presents a multielement annular ring ultrasound transducer formed by individual high-frequency PMUTs (17.5 MHz in air and 8.7 MHz in liquid) intended for high-precision axial focalization and high-performance ultrasound imaging. The prototype has five independent multielement rings fabricated by a monolithic process over CMOS, allowing for a very compact and robust design. Crosstalk between rings is under 56 dB, which guarantees an efficient beam focusing on a range between 1.4 mm and 67 µm. The presented PMUT-on-CMOS annular array with an overall diameter down to 669 µm achieves an output pressure in liquid of 4.84 kPa/V/mm2 at 1.5 mm away from the array when the five channels are excited together, which is the largest reported for PMUTs. Pulse-echo experiments towards high-resolution imaging are demonstrated using the central ring as a receiver. With an equivalent diameter of 149 µm, this central ring provides high receiving sensitivity, 441.6 nV/Pa, higher than that of commercial hydrophones with equivalent size. A 1D ultrasound image using two channels is demonstrated, with maximum received signals of 7 mVpp when a nonintegrated amplifier is used, demonstrating the ultrasound imaging capabilities.

A Dual-mode 2D Matrix Array for Ultrasound Image-guided Noninvasive Therapy

Focused ultrasound (FUS) lacks reliable real-time image guidance, which hinders the development of non-invasive ultrasound treatment in many important clinical applications. A dual-mode ultrasound array, capable of both imaging and therapy offers a new and reliable strategy for image-guided ultrasound therapy applications. The strategy has the advantages of real-time use, low cost, portability and inherent registration between imaging and therapeutic coordinate systems. In this work, a dual-mode two-dimensional (2D) matrix array with 1 MHz center frequency and 256 elements for ultrasound image-guided non-invasive therapy is reported. The array can provide three-dimensional (3D) volumetric ultrasound imaging and 3D focus control. Ultrasound imaging and therapeutic applications for the brain of small animals demonstrated the multi-functional capability of the dual-mode 2D matrix array. A method of rat brain positioning based on ultrasound imaging was proposed and verified. Transcranial ultrasound image-guided bloodbrain barrier (BBB) opening of multiple-targets was achieved in vivo, using the proposed dual-mode 2D array. The obtained results indicate that the dual-mode 2D matrix array is a promising method for practical use in ultrasound image-guided non-invasive therapy applications.

Acupoint-brain (acubrain) mapping: Common and distinct cortical language regions activated by focused ultrasound stimulation on two language-relevant acupoints

Acupuncture, taking the advantage of modality-specific neural pathways, has shown promising results in the treatment of brain disorders that affect different modalities such as pain and vision. However, the precise underlying mechanisms of within-modality neuromodulation of acupoints on human high-order cognition remain largely unknown. In the present study, we used a non-invasive and easy-operating method, focused ultrasound, to stimulate two language-relevant acupoints, namely GB39 (Xuanzhong) and SJ8 (Sanyangluo), of thirty healthy adults. The effect of focused ultrasound stimulation (FUS) on brain activation was examined by functional magnetic resonance imaging (fMRI). We found that stimulating GB39 and SJ8 by FUS evoked overlapping but distinct brain activation patterns. Our findings provide a major step toward within-modality (in this case, language) acupoint-brain (acubrain) mapping and shed light on to the potential use of FUS as a personalized treatment option for brain disorders that affect high-level cognitive functions.

Novel Bandwidth Expander Supported Power Amplifier for Wideband Ultrasound Transducer Devices

Ultrasound transducer devices have their own frequency ranges, depending on the applications and specifications, due to penetration depth, sensitivity, and image resolution. For imaging applications, in particular, the transducer devices are preferable to have a wide bandwidth due to the specific information generated by the tissue or blood vessel structures. To support these ultrasound transducer devices, ultrasound power amplifier hardware with a wide bandwidth can improve the transducer performance. Therefore, we developed a new bandwidth expander circuit using specially designed switching architectures to increase the power amplifier bandwidth. The measured bandwidth of the power amplifier with the help of the bandwidth expander circuit increased by 56.9%. In addition, the measured echo bandwidths of the 15-, 20-, and 25-MHz transducer devices were increased by 8.1%, 6.0%, and 9.8%, respectively, with the help of the designed bandwidth expander circuit. Therefore, the designed architecture could help an ultrasound system hardware with a wider bandwidth, thus supporting the use of different frequency ultrasound transducer devices with a single developed ultrasound system.

Therapeutic Potential of Ultrasound Neuromodulation in Decreasing Neuropathic Pain: Clinical and Experimental Evidence

Background

For more than seven decades, ultrasound has been used as an imaging and diagnostic tool. Today, new technologies, such as focused ultrasound (FUS) neuromodulation, have revealed some innovative, potential applications. However, those applications have been barely studied to deal with neuropathic pain (NP), a cluster of chronic pain syndromes with a restricted response to conventional pharmaceuticals.

Objective

To analyze the therapeutic potential of low-intensity (LIFUS) and high-intensity (HIFUS) FUS for managing NP.

Methods

We performed a narrative review, including clinical and experimental ultrasound neuromodulation studies published in three main database repositories.

Discussion

Evidence shows that FUS may influence several mechanisms relevant for neuropathic pain management such as modulation of ion channels, glutamatergic neurotransmission, cerebral blood flow, inflammation and neurotoxicity, neuronal morphology and survival, nerve regeneration, and remyelination. Some experimental models have shown that LIFUS may reduce allodynia after peripheral nerve damage. At the same time, a few clinical studies support its beneficial effect on reducing pain in nerve compression syndromes. In turn, Thalamic HIFUS ablation can reduce NP from several etiologies with minor side-effects, but some neurological sequelae might be permanent. HIFUS is also useful in lowering non-neuropathic pain in several disorders.

Conclusion

Although an emerging set of studies brings new evidence on the therapeutic potential of both LIFUS and HIFUS for managing NP with minor side-effects, we need more controlled clinical trials to conclude about its safety and efficacy.

S-MRUT: Sectored-Multiring Ultrasonic Transducer for Selective Powering of Brain Implants

One of the main challenges of the current ultrasonic transducers for powering brain implants is the complexity of focusing ultrasonic waves in various axial and lateral directions. The available transducers usually use electrically controlled phased array for beamforming the ultrasonic waves, which increases the complexity of the system even further. In this article, we propose a straightforward solution for selective powering of brain implants to remove the complexity of conventional phased arrays. Our approach features a Sectored-Multiring Ultrasonic Transducer (S-MRUT) on a single piezoelectric sheet, specifically designed for powering implantable devices for optogenetics in freely moving animals. The proposed unidirectional S-MRUT is capable of focusing the ultrasonic waves on brain implants located at different depths and regions of the brain. The S-MRUT is designed based on Fresnel Zone Plate (FZP) theory, simulated in COMSOL, and fabricated with the microfabrication process. The acoustic profile of the seven different configurations of the S-MRUT was measured using a hydrophone with the total number of 7436 grid points. The measurements show the ability of the proposed S-MRUT to sweep the focus point of the acoustic waves in the axial direction in depths of 1 - 3 mm, which is suitable for powering implants in the striatum of the mouse. Furthermore, the proposed S-MRUT demonstrates a steering area with an average radius of 0.862 mm and 0.678 mm in experiments and simulations, respectively. The S-MRUT is designed with the size of 3.8×3.8×0.5 mm³ and the weight of 0.054gr , showing that it is compact and light enough to be worn by a mouse. Finally, the S-MRUT was tested in our measurement setup, where it successfully transfers sufficient power to a 2.8-mm³ optogentic stimulator to turn on a micro-LED on the stimulator.

Ultrasound for the Brain: A Review of Physical and Engineering Principles, and Clinical Applications

The emergence of new ultrasound technologies has improved our understanding of the brain functions and offered new opportunities for the treatment of brain diseases. Ultrasound has become a valuable tool in preclinical animal and clinical studies as it not only provides information about the structure and function of brain tissues but can also be used as a therapy alternative for brain diseases. High-resolution cerebral flow images with high sensitivity can be acquired using novel functional ultrasound and super-resolution ultrasound imaging techniques. The noninvasive treatment of essential tremors has been clinically approved and it has been demonstrated that the ultrasound technology can revolutionize the currently existing treatment methods. Microbubble-mediated ultrasound can remotely open the blood-brain barrier enabling targeted drug delivery in the brain. More recently, ultrasound neuromodulation received a great amount of attention due to its noninvasive and deep penetration features and potential therapeutic benefits. This review provides a thorough introduction to the current state-of-the-art research on brain ultrasound and also introduces basic knowledge of brain ultrasound including the acoustic properties of the brain/skull and engineering techniques for ultrasound. Ultrasound is expected to play an increasingly important role in the diagnosis and therapy of brain diseases.

Fiber-Based Clock Synchronization Method for Medical Ultrasound System

Brain ultrasound has attracted great attention recently due to its noninvasive treatment function for brain diseases. However, ultrasound is still difficult to pass through an intact skull. Phase correction is recognized as an effective method for skull compensation. Half-wavelength pitch transducer is important for the phase correction and, hence, thousands of elements array is required to cover large area human tissue. The clock synchronization between elements is crucial for the phase correction; however, the traditional clock scheme which is designed for 128- or 256-element system is not suitable for thousands of elements. In addition, the clock scheme needs to be magnetic resonance imaging (MRI) compatible since MRI-guided intervention is becoming a routine operation for the brain ultrasound. This study is the first to propose an optical fiber-based clock synchronization method for MRI-guided ultrasound array system. The optical fiber not only distributes the clock but also sets up a link to transmit the data for ultrasound beamformer. The link is full-duplex so both the clock and the data can be transmitted and received simultaneously. The precision of clock synchronization is less than 557 ps when using 50 MHz clock, and the period jitter of the clock is less than 10 ps (rms). Multiple 128- or 256-channel ultrasonic systems can be synchronized, and the error between the channels can be less than 10 ns when using 1-MHz ultrasound transducer. The system can work in an MRI scanning room and communicate with a console via only one fiber. In vivo primate animal study has been achieved, and it has been proven that the proposed clock scheme is suitable for MRI-guided large-scale ultrasound array system.

Transcranial Focused Ultrasound for Noninvasive Neuromodulation of the Visual Cortex

Currently, blindness cannot be cured and patients' living quality can be compromised severely. Ultrasonic (US) neuromodulation is a promising technology for the development of noninvasive cortical visual prosthesis. We investigated the feasibility of transcranial focused ultrasound (tFUS) for noninvasive stimulation of the visual cortex (VC) to develop improved visual prosthesis. tFUS was used to successfully evoke neural activities in the VC of both normal and retinal degenerate (RD) blind rats. Our results showed that blind rats showed more robust responses to ultrasound stimulation when compared with normal rats. ( , two-sample t-test). Three different types of ultrasound waveforms were used in the three experimental groups. Different types of cortical activities were observed when different US waveforms were used. In all rats, when stimulated with continuous ultrasound waves, only short-duration responses were observed at "US on and off" time points. In comparison, pulsed waves (PWs) evoked longer low-frequency responses. Testing different parameters of PWs showed that a pulse repetition frequency higher than 100 Hz is required to obtain the low-frequency responses. Based on the observed cortical activities, we inferred that acoustic radiation force (ARF) is the predominant physical mechanism of ultrasound neuromodulation.

Inter-Stage Output Voltage Amplitude Improvement Circuit Integrated with Class-B Transmit Voltage Amplifier for Mobile Ultrasound Machines

Piezoelectric transducers are triggered by the output voltage signal of a transmit voltage amplifier (TVA). In mobile ultrasound instruments, the sensitivity of piezoelectric transducers is a critical parameter under limited power supply from portable batteries. Therefore, the enhancement of the output voltage amplitude of the amplifier under limited power supply could increase the sensitivity of the piezoelectric transducer. Several-stage TVAs are used to increase the voltage amplitude. However, inter-stage design issues between each TVA block may reduce the voltage amplitude and bandwidth because the electronic components of the amplifier are nonlinearly operated at the desired frequency ranges. To compensate for this effect, we propose a novel inter-stage output voltage amplitude improvement (OVAI) circuit integrated with a class-B TVA circuit. We performed fundamental A-mode pulse-echo tests using a 15-MHz immersion-type piezoelectric transducer to verify the design. The echo amplitude and bandwidth when using an inter-stage OVAI circuit integrated with a class-B TVA circuit (696 mV_PP and 29.91%, respectively) were higher than those obtained when using only the class-B TVA circuit (576 mV_PP and 24.21%, respectively). Therefore, the proposed OVAI circuit could be beneficial for increasing the output amplitude of the class-B TVA circuit for mobile ultrasound machines.

Ultrasonic Retinal Neuromodulation and Acoustic Retinal Prosthesis

Ultrasound is an emerging method for non-invasive neuromodulation. Studies in the past have demonstrated that ultrasound can reversibly activate and inhibit neural activities in the brain. Recent research shows the possibility of using ultrasound ranging from 0.5 to 43 MHz in acoustic frequency to activate the retinal neurons without causing detectable damages to the cells. This review recapitulates pilot studies that explored retinal responses to the ultrasound exposure, discusses the advantages and limitations of the ultrasonic stimulation, and offers an overview of engineering perspectives in developing an acoustic retinal prosthesis. For comparison, this article also presents studies in the ultrasonic stimulation of the visual cortex. Despite that, the summarized research is still in an early stage; ultrasonic retinal stimulation appears to be a viable technology that exhibits enormous therapeutic potential for non-invasive vision restoration.

New Sm-PMN-PT Ceramic-Based 2-D Array for Low-Intensity Ultrasound Therapy Application

A two-dimensional (2-D) array with a small pitch (approximately 0.5λ in medium) can achieve complete 3-D control of ultrasound beams without grating lobes and enable the generation of multiple focal spots simultaneously, which is a desired tool for noninvasive therapy. However, the large electrical impedance of 2-D array elements owing to their small size results in a low energy transfer efficiency between a 2-D array and an electrical system, thereby limiting their practical applications. This article presents the development of a 1-MHz 256-element 2-D array ultrasonic transducer of low electrical impedance based on a new Sm-doped Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (Sm-PMN-PT) piezoceramic with ultrahigh dielectric permittivity. The electrical impedance of the array element is decreased by 3.4 times as the Sm-PMN-PT replacing commercial PZT-5H. Consequently, the output acoustic pressure of the 2-D array made of Sm-PMN-PT ceramic is approximately twice that of the 2-D array made of PZT-5H ceramic under the same excitation conditions. Array elements are spaced at a 1.1-mm pitch ( 0.71λ in water), enabling a large steering range of the ultrasound beam. A multiple-target blood-brain barrier opening in vivo is demonstrated using the proposed 2-D array with electronic focusing and steering. The obtained results indicate that the 2-D array made of Sm-PMN-PT ceramic is promising for practical use in low-intensity ultrasound therapy applications.

Wireless Ultrasound Surgical System with Enhanced Power and Amplitude Performances

A wireless ultrasound surgical system (WUSS) with battery modules requires efficient power consumption with appropriate cutting effects during surgical operations. Effective cutting performances of the ultrasound transducer (UT) should be produced for ultrasound surgical knives for effective hemostasis performance and efficient dissection time. Therefore, we implemented a custom-made UT with piezoelectric material and re-poling process, which is applied to enhance the battery power consumption and output amplitude performances of the WUSS. After the re-poling process of the UT, the quality factor increased from 1231.1 to 2418 to minimize the unwanted heat generation. To support this UT, we also developed a custom-made generator with a transformer and developed 2nd harmonic termination circuit, control microcontroller with an advanced reduced instruction set computer machine (ARM) controller, and battery management system modules to produce effective WUSS performances. The generator with a matching circuit in the WUSS showed a peak-to-peak output voltage and current amplitude of 166 V and 1.12 A, respectively, at the resonant frequency. The performance with non-contact optical vibrators was also measured. In the experimental data, the developed WUSS reduced power consumption by 3.6% and increased the amplitude by 20% compared to those of the commercial WUSS. Therefore, the improved WUSS performances could be beneficial for hemostatic performance and dissection time during surgical operation because of the developed UT with a piezoelectric material and re-poling process.

Ultrasonic Neuromodulation and Sonogenetics: A New Era for Neural Modulation

Non-invasive ultrasonic neural modulation (UNM), a non-invasive technique with enhanced spatial focus compared to conventional electrical neural modulation, has attracted much attention in recent decades and might become the mainstream regimen for neurological disorders. However, as ultrasonic bioeffects and its adjustments are still unclear, it remains difficult to be extensively applied for therapeutic purpose, much less in the setting of human skull. Hence to comprehensively understand the way ultrasound exerts bioeffects, we explored UNM from a basic perspective by illustrating the parameter settings and the underlying mechanisms. In addition, although the spatial resolution and precision of UNM are considerable, UNM is relatively non-specific to tissue or cell type and shows very low specificity at the molecular level. Surprisingly, Ibsen et al. (2015) first proposed the concept of sonogenetics, which combined UNM and mechanosensitive (MS) channel protein. This emerging approach is a valuable improvement, as it may markedly increase the precision and spatial resolution of UNM. It seemed to be an inspiring tool with high accuracy and specificity, however, little information about sonogenetics is currently available. Thus, in order to provide an overview of sonogenetics and prompt the researches on UNM, we summarized the potential mechanisms from a molecular level.

Low-Intensity Focused Ultrasound Stimulation Treatment Decreases Blood Pressure in Spontaneously Hypertensive Rats

OBJECTIVE

We applied low-intensity focused ultrasound (LIFU) stimulation of the ventrolateral periaqueductal gray (vlPAG) in spontaneously hypertensive rats (SHRs) model to demonstrate the feasibility of LIFU stimulation to decrease blood pressure (BP).

METHODS

The rats were treated with LIFU stimulation for 20 min every day for one week. The change of BP and heart rate (HR) were recorded to evaluate the antihypertensive effect. Then the plasma levels of epinephrine (EPI), norepinephrine (NE), and angiotensin II (ANGII) were measured to evaluate the activity of the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). The c-fos immunofluorescence assay was performed to investigate the antihypertensive nerve pathway. Moreover, the biological safety of ultrasound sonication was examined.

RESULTS

The LIFU stimulation induced a significant reduction of BP in 8 SHRs. The mean systolic blood pressure (SBP) was reduced from 170 ± 4 mmHg to 128 ± 4.5 mmHg after a one-week treatment, p < 0.01. The activity of SNS and RAS were also inhibited. The results of the c-fos immunofluorescence assay showed that US stimulation of the vlPAG significantly enhanced the neuronal activity both in vlPAG and caudal ventrolateral medulla (CVLM) regions. And the US stimulation used in this study did not cause significant tissue damage, hemorrhage and cell apoptosis in the sonication region.

CONCLUSION

The results support that LIFU stimulation of the vlPAG could relieve hypertension in SHRs.

SIGNIFICANCE

The LIFU stimulation of the vlPAG could potentially be a new alternative non-invasive device therapy for hypertension.

Mobile Wireless Low-intensity Transcranial Ultrasound Stimulation System for Freely Behaving Small Animals

Transcranial ultrasound stimulation (tUS) is a promising noninvasive approach to modulate brain circuits. While low-intensity tUS is putatively safe and has already been used for human participants, pre-clinical studies that aim to determine the effects of tUS on the brain still need to be carried out. Conventional tUS stimulation, however, requires the use of the anesthetized or immobilized animal model, which can place considerable restrictions on behavior. Thus, this work presents a portable, low cost, wireless system to achieve ultrasound brain stimulation in freely behaving animals. The tUS system was developed based on a commercial 16 MHz microcontroller and amplifier circuit. The acoustic wave with a central frequency of 450 kHz was generated from a 5mm PZT with a peak pressure of 426 kPa. The wireless tUS with a total weight of 20 g was placed on the back of the rat allowing the animal a full range of unimpeded motion. The mobile ultrasound system was able to induce a robust ear movement as a response to stimulation of the motor cortex. The outcome demonstrates the ability of wireless tUS to modulate the brain circuit of a freely behaving rat. The portability of the whole system provides a more natural environment for investigating the effect of tUS on behavior and chronic studies.

Multi-Ring Ultrasonic Transducer on a Single Piezoelectric Disk For Powering Biomedical Implants

This paper presents a novel ultrasonic transmitter with the ability of focusing ultrasonic waves for maximum power transmission at different depths for brain neurostimula-tor implants. The most important advantages of the proposed multi-ring ultrasonic transducer (MRUT) is its simplicity and no requirement of any lens or air cavity for focusing the ultrasonic waves. Furthermore, adjusting the focal point compared to the conventional transducers is significantly easier, especially as the location of implants may vary due to, for example, head movement or the need of using these implants at different depths. By the use of multiple rings on a single piezoelectric disk in our transducer, not only more focused ultrasound beams can be achieved, but also the side lobes can be diminished by exciting each rings with different electrical signal. The proposed transmitter is envisioned to be used for optogenetic stimulation of neurons in freely-moving animals.

Skull Impact on the Ultrasound Beam Profile of Transcranial Focused Ultrasound Stimulation

Transcranial focused ultrasound stimulation (tFUS) is a promising noninvasive neuromodulation tool for targeting brain regions with millimeter-scale spatial resolutions. In conventional tFUS studies, a focused ultrasound beam generated by an external ultrasound transducer is delivered to the neural target. In tFUS, ultrasound should travel through the skull that features large attenuation and different acoustic impedance compared with the soft tissue, thereby resulting in acoustic impedance mismatch and reflections. In this paper, we study the impact of the rat skull on the ultrasound beam profile generated by both focused and unfocused (but with a natural focus) transducers at a wide sonication frequency (f_p) range of 0.5-9.5 MHz. At different axial and lateral distances from the transducers, we measured ultrasound intensity profiles of three transducers operating at f_ps of 0.5 MHz, 1.2 MHz and 9.5 MHz with and without the skull. Our results showed that ultrasound beam profiles were significantly distorted by the skull. The transmission factor due to skull attenuation was measured 0.79,0.34 and 0.03 at f_ps of 0.5 MHz, 1.2 MHz and 9.5 MHz, respectively, when the skull was close to transducers focal zones.

Oscillotherapeutics - Time-targeted interventions in epilepsy and beyond

Oscillatory brain activities support many physiological functions from motor control to cognition. Disruptions of the normal oscillatory brain activities are commonly observed in neurological and psychiatric disorders including epilepsy, Parkinson's disease, Alzheimer's disease, schizophrenia, anxiety/trauma-related disorders, major depressive disorders, and drug addiction. Therefore, these disorders can be considered as common oscillation defects despite having distinct behavioral manifestations and genetic causes. Recent technical advances of neuronal activity recording and analysis have allowed us to study the pathological oscillations of each disorder as a possible biomarker of symptoms. Furthermore, recent advances in brain stimulation technologies enable time- and space-targeted interventions of the pathological oscillations of both neurological disorders and psychiatric disorders as possible targets for regulating their symptoms.

A Comprehensive Study of Ultrasound Transducer Characteristics in Microscopic Ultrasound Neuromodulation

In order to improve the spatial resolution of transcranial focused ultrasound stimulation (tFUS), we have recently proposed microscopic ultrasound stimulation (μUS). In μUS, either an electronically phased array of ultrasound transducers or several millimeter-sized focused transducers are placed on the brain surface or sub-millimeter-sized transducers are implanted inside the brain tissue to steer and deliver a focused ultrasound pressure directly to the neural target. A key element in both tFUS and μUS is the ultrasound transducer that converts electrical power to acoustic pressure. The literature lacks a comprehensive study (in a quantitative manner) of the transducer characteristics, such as dimension, focusing, acoustic matching, backing material, and sonication frequency (fp), in the μUS. This paper studies the impact of these design parameters on the acoustic beam profile of millimeter-sized transducers with the emphasis on the stimulation spatial resolution and energy efficiency, which is defined as the μUS figure-of-merit (FoM). For this purpose, disc-shaped focused and unfocused piezoelectric (PZT-5A) transducers with different dimension (diameter, thickness), backing material (PCB, air) and acoustic matching in the frequency range of 2.2-9.56 MHz were fabricated. Our experimental studies with both water and sheep brain phantom medium demonstrate that acoustically matched focused transducers with high quality factor are desirable for μUS, as they provide fine spatial resolution and high acoustic intensities with low input electrical power levels (i.e., high FoM).

Brain Modulatory Effects by Low-Intensity Transcranial Ultrasound Stimulation (TUS): A Systematic Review on Both Animal and Human Studies

Background and objective: Low Intensity Transcranial Ultrasound Stimulation (TUS) is a new form of non-invasive brain modulation with promising data; however, systematic reviews on the brain modulatory effects of TUS on both animals and humans have not been well-conducted. We aimed to conduct a systematic review on the studies using the TUS to modulate the brain functions and associated behavioral changes in both animals and humans. Methods: A literature search for published studies in the past 10 years was conducted. Two authors independently reviewed the relevant articles. Data were extracted and qualitatively summarized. Quality of studies was assessed by the SYRCLE's risk of bias tool for preclinical studies or the PEDro scale for clinical studies. Results: A total of 24 animal studies (506 animals) and 11 human studies (213 subjects) were included. Findings based on most animal studies demonstrated the excitatory or suppressive modulatory effects of ultrasonic stimulations on motor cortex, somatosensory cortex, thalamus, prefrontal cortex, auditory, and visual areas. Brain modulatory effects also were found among healthy human subjects in seven studies and two clinical studies suggested TUS may result in potential benefits on patients with disorder of consciousness or chronic pain. The safety concerns of TUS seem to be minor based on the human studies. Conclusions: TUS appears to be a viable technique in modulating the brain functions; however, research on TUS is still in its early stages, especially in human studies. Parameters need to be optimized before launching systematic investigations in humans.

A Novel Racing Array Transducer for Noninvasive Ultrasonic Retinal Stimulation: A Simulation Study

Neurostimulation has proved to be an effective method for the restoration of visual perception lost due to retinal diseases. However, the clinically available retinal neurostimulation method is based on invasive electrodes, making it a high-cost and high-risk procedure. Recently, ultrasound has been demonstrated to be an effective way to achieve noninvasive neurostimulation. In this work, a novel racing array transducer with a contact lens shape is proposed for ultrasonic retinal stimulation. The transducer is flexible and placed outside the eyeball, similar to the application of a contact lens. Ultrasound emitted from the transducer can reach the retina without passing through the lens, thus greatly minimizing the acoustic absorption in the lens. The discretized Rayleigh–Sommerfeld method was employed for the acoustic field simulation, and patterned stimulation was achieved. A 5 MHz racing array transducer with different element numbers was simulated to optimize the array configuration. The results show that a 512-element racing array is the most appropriate configuration considering the necessary tradeoff between the element number and the stimulation resolution. The stimulation resolution at a focus of 24 mm is about 0.6 mm. The obtained results indicate that the proposed racing array design of the ultrasound transducer can improve the feasibility of an ultrasound retinal prosthesis.