Focused ultrasound-mediated brain genome editing.

Gene editing in the brain has been challenging because of the restricted transport imposed by the blood-brain barrier (BBB). Current approaches mainly rely on local injection to bypass the BBB. However, such administration is highly invasive and not amenable to treating certain delicate regions of the brain. We demonstrate a safe and effective gene editing technique by using focused ultrasound (FUS) to transiently open the BBB for the transport of intravenously delivered CRISPR/Cas9 machinery to the brain.

Focused ultrasound excites action potentials in mammalian peripheral neurons in part through the mechanically gated ion channel PIEZO2.

Neurons of the peripheral nervous system (PNS) are tasked with diverse roles, from encoding touch, pain, and itch to interoceptive control of inflammation and organ physiology. Thus, technologies that allow precise control of peripheral nerve activity have the potential to regulate a wide range of biological processes. Noninvasive modulation of neuronal activity is an important translational application of focused ultrasound (FUS). Recent studies have identified effective strategies to modulate brain circuits; however, reliable parameters to control the activity of the PNS are lacking. To develop robust noninvasive technologies for peripheral nerve modulation, we employed targeted FUS stimulation and electrophysiology in mouse ex vivo skin-saphenous nerve preparations to record the activity of individual mechanosensory neurons. Parameter space exploration showed that stimulating neuronal receptive fields with high-intensity, millisecond FUS pulses reliably and repeatedly evoked one-to-one action potentials in all peripheral neurons recorded. Interestingly, when neurons were classified based on neurophysiological properties, we identified a discrete range of FUS parameters capable of exciting all neuronal classes, including myelinated A fibers and unmyelinated C fibers. Peripheral neurons were excited by FUS stimulation targeted to either cutaneous receptive fields or peripheral nerves, a key finding that increases the therapeutic range of FUS-based peripheral neuromodulation. FUS elicited action potentials with millisecond latencies compared with electrical stimulation, suggesting ion channel­mediated mechanisms. Indeed, FUS thresholds were elevated in neurons lacking the mechanically gated channel PIEZO2. Together, these results demonstrate that transcutaneous FUS drives peripheral nerve activity by engaging intrinsic mechanotransduction mechanisms in neurons [B. U. Hoffman, PhD thesis, (2019)].

Displacement and functional ultrasound (fUS) imaging of displacement-guided focused ultrasound (FUS) neuromodulation in mice.

Focused ultrasound (FUS) stimulation is a promising neuromodulation technique with the merits of non-invasiveness, high spatial resolution, and deep penetration depth. However, simultaneous imaging of FUS-induced brain tissue displacement and the subsequent effect of FUS stimulation on brain hemodynamics has proven challenging thus far. In addition, earlier studies lack in situ confirmation of targeting except for the magnetic resonance imaging-guided FUS system-based studies. The purpose of this study is 1) to introduce a fully ultrasonic approach to in situ target, modulate neuronal activity, and monitor the resultant neuromodulation effect by respectively leveraging displacement imaging, FUS, and functional ultrasound (fUS) imaging, and 2) to investigate FUS-evoked cerebral blood volume (CBV) response and the relationship between CBV and displacement. We performed displacement imaging on craniotomized mice to confirm the in situ targeting for neuromodulation site. We recorded hemodynamic responses evoked by FUS while fUS imaging revealed an ipsilateral CBV increase that peaks at 4 s post-FUS. We report a stronger hemodynamic activation in the subcortical region than cortical, showing good agreement with a brain elasticity map that can also be obtained using a similar methodology. We observed dose-dependent CBV responses with peak CBV, activated area, and correlation coefficient increasing with the ultrasonic dose. Furthermore, by mapping displacement and hemodynamic activation, we found that displacement colocalized and linearly correlated with CBV increase. The findings presented herein demonstrated that FUS evokes ipsilateral hemodynamic activation in cortical and subcortical depths while the evoked hemodynamic responses colocalize and correlate with FUS-induced displacement. We anticipate that our findings will help consolidate accurate targeting as well as shedding light on one of the mechanisms behind FUS modulation, i.e., how FUS mechanically displaces brain tissue affecting cerebral hemodynamics and thereby its associated connectivity.

Focused ultrasound-mediated blood-brain barrier opening is safe and feasible with moderately hypofractionated radiotherapy for brainstem diffuse midline glioma.

BACKGROUND: Diffuse midline glioma (DMG) is a pediatric tumor with dismal prognosis. Systemic strategies have been unsuccessful and radiotherapy (RT) remains the standard-of-care. A central impediment to treatment is the blood-brain barrier (BBB), which precludes drug delivery to the central nervous system (CNS). Focused ultrasound (FUS) with microbubbles can transiently and non-invasively disrupt the BBB to enhance drug delivery. This study aimed to determine the feasibility of brainstem FUS in combination with clinical doses of RT. We hypothesized that FUS-mediated BBB-opening (BBBO) is safe and feasible with 39 Gy RT. METHODS: To establish a safety timeline, we administered FUS to the brainstem of non-tumor bearing mice concurrent with or adjuvant to RT; our findings were validated in a syngeneic brainstem murine model of DMG receiving repeated sonication concurrent with RT. The brainstems of male B6 (Cg)-Tyrc-2J/J albino mice were intracranially injected with mouse DMG cells (PDGFB+, H3.3K27M, p53-/-). A clinical RT dose of 39 Gy in 13 fractions (39 Gy/13fx) was delivered using the Small Animal Radiation Research Platform (SARRP) or XRAD-320 irradiator. FUS was administered via a 0.5 MHz transducer, with BBBO and tumor volume monitored by magnetic resonance imaging (MRI). RESULTS: FUS-mediated BBBO did not affect cardiorespiratory rate, motor function, or tissue integrity in non-tumor bearing mice receiving RT. Tumor-bearing mice tolerated repeated brainstem BBBO concurrent with RT. 39 Gy/13fx offered local control, though disease progression occurred 3-4 weeks post-RT. CONCLUSION: Repeated FUS-mediated BBBO is safe and feasible concurrent with RT. In our syngeneic DMG murine model, progression occurs, serving as an ideal model for future combination testing with RT and FUS-mediated drug delivery.

Combining brain perturbation and neuroimaging in non-human primates.

Brain perturbation studies allow detailed causal inferences of behavioral and neural processes. Because the combination of brain perturbation methods and neural measurement techniques is inherently challenging, research in humans has predominantly focused on non-invasive, indirect brain perturbations, or neurological lesion studies. Non-human primates have been indispensable as a neurobiological system that is highly similar to humans while simultaneously being more experimentally tractable, allowing visualization of the functional and structural impact of systematic brain perturbation. This review considers the state of the art in non-human primate brain perturbation with a focus on approaches that can be combined with neuroimaging. We consider both non-reversible (lesions) and reversible or temporary perturbations such as electrical, pharmacological, optical, optogenetic, chemogenetic, pathway-selective, and ultrasound based interference methods. Method-specific considerations from the research and development community are offered to facilitate research in this field and support further innovations. We conclude by identifying novel avenues for further research and innovation and by highlighting the clinical translational potential of the methods.

Modeling Pulse Wave Propagation Through a Stenotic Artery With Fluid Structure Interaction: A Validation Study Using Ultrasound Pulse Wave Imaging.

Pulse wave imaging (PWI) is an ultrasound-based method that allows spatiotemporal mapping of the arterial pulse wave propagation, from which the local pulse wave velocity (PWV) can be derived. Recent reports indicate that PWI can help the assessment of atherosclerotic plaque composition and mechanical properties. However, the effect of the atherosclerotic plaque's geometry and mechanics on the arterial wall distension and local PWV remains unclear. In this study, we investigated the accuracy of a finite element (FE) fluid-structure interaction (FSI) approach to predict the velocity of a pulse wave propagating through a stenotic artery with an asymmetrical plaque, as quantified with PWI method. Experiments were designed to compare FE-FSI modeling of the pulse wave propagation through a stenotic artery against PWI obtained with manufactured phantom arteries made of polyvinyl alcohol (PVA) material. FSI-generated spatiotemporal maps were used to estimate PWV at the plaque region and compared it to the experimental results. Velocity of the pulse wave propagation and magnitude of the wall distension were correctly predicted with the FE analysis. In addition, findings indicate that a plaque with a high degree of stenosis (>70%) attenuates the propagation of the pulse pressure wave. Results of this study support the validity of the FE-FSI methods to investigate the effect of arterial wall structural and mechanical properties on the pulse wave propagation. This modeling method can help to guide the optimization of PWI to characterize plaque properties and substantiate clinical findings.

Fast qualitative two-dimensional mapping of ultrasound fields with acoustic cavitation-enhanced ultrasound imaging.

Characterization of ultrasound fields is a routine procedure for both diagnostic and therapeutic ultrasound. Quantitative field mapping with a calibrated hydrophone and multi-axis positioning system can be difficult and time consuming. In this study, the use of acoustic cavitation field mapping as a qualitative surrogate to acoustic pressure field mapping, albeit without acoustic pressure values is demonstrated. This technique allows for fast qualitative mapping of ultrasound fields and thereby functionality of the corresponding transducers, in a matter of seconds. In addition, this technique could be used to rapidly image in vivo acoustic cavitation fields during therapeutic ultrasound applications.

Assessment of arterial stiffness in periodontitis using a novel pulse wave imaging methodology.

AIM: We investigated the cross-sectional relationship between periodontal status and arterial stiffness, assessed through a novel Pulse Wave Imaging methodology. METHODS: Eighty volunteers were enrolled (39% male, age range 24-78 years) and 33 pairs were formed of periodontitis patients/periodontally healthy controls, matched by age and gender. A full-mouth periodontal examination was performed and the degree of stiffness of the right and left carotid arteries was assessed by measuring pulse wave velocity (PWV) and the uniformity in pulse wave propagation (R2 ). Wilcoxon signed-rank tests for paired observations were used to compare periodontitis patients and healthy controls. Univariate and multivariate analyses were performed to analyze the association between PWV and R2 and potential explanatory variables. RESULTS: Patients with periodontitis had a statistically significantly lower uniformity in wave propagation (R2 ) than controls (p = .01), but PWV did not differ between the two groups. Univariate analysis showed a significant negative association between R2 and periodontitis, body mass index and smoking; periodontitis remained statistically associated with R2 in the multivariate analyses. CONCLUSIONS: Patients with periodontitis and no established cardiovascular disease presented with lower degree of uniformity in the transmission of the pulse wave through the carotid arteries, suggesting an association between periodontitis and arterial stiffness/functional alterations.

Assessing the Stability of Aortic Aneurysms with Pulse Wave Imaging.

Purpose To assess whether the stability of murine aortic aneurysms is associated with the homogeneity of pulse wave propagation within the saccular wall. Materials and Methods All animal procedures were approved by the institutional Animal Care and Use Committee. Apolipoprotein E and tissue inhibitor of metalloproteinases-1 knockout mice (n = 26) were infused with angiotensin II by using subcutaneously implanted osmotic pumps, with an additional control mouse used for histologic examination (n = 1). Pulse wave imaging (PWI) was performed just before infusion and 15 days after infusion by using 40-MHz ultrasonography at 8000 frames per second (with electrocardiographic gating). Aneurysm appearance on B-mode images was monitored every 2-3 days for 30 days. On the basis of B-mode images obtained after 30 days, aneurysms were deemed to have been unstable if they had ruptured; otherwise, they were deemed stable. Statistical significance was assessed by using two-tailed t tests. Results In normal aortas, the pulse waves propagated at relatively constant velocities (mean ± standard deviation, 2.8 m/sec ± 0.9). Fifteen days after infusion, all mice had developed aneurysms, with significant (P < .001/12) changes in maximum anterior-posterior diameter (increase of 54.9% ± 2.5) and pulse wave velocity (PWV) (decrease of 1.3 m/sec ± 0.8). While there was no significant difference in these parameters (P = .45 for diameter and P = .55 for PWV) between stable aneurysms (n = 12) and unstable aneurysms (n = 14), the standard deviation of the high-resolution PWV was significantly higher (P < .001/12) in unstable aneurysms (5.7 m/sec ± 1.6) than in stable ones (3.2 m/sec ± 0.9). Conclusion High-resolution PWI was used to measure the local homogeneity of pulse wave propagation within the saccular wall, which is lower in unstable aneurysms than in stable ones. Hence, if proven to add additional information beyond size and appearance in human studies, PWI could potentially be used to assess the stability of aneurysms by providing information that is complementary to the anatomic data obtained with conventional B-mode imaging. © RSNA, 2016 Online supplemental material is available for this article.

Noninvasive and localized neuronal delivery using short ultrasonic pulses and microbubbles.

Focused ultrasound activation of systemically administered microbubbles is a noninvasive and localized drug delivery method that can increase vascular permeability to large molecular agents. Yet the range of acoustic parameters responsible for drug delivery remains unknown, and, thus, enhancing the delivery characteristics without compromising safety has proven to be difficult. We propose a new basis for ultrasonic pulse design in drug delivery through the blood-brain barrier (BBB) that uses principles of probability of occurrence and spatial distribution of cavitation in contrast to the conventionally applied magnitude of cavitation. The efficacy of using extremely short (2.3 µs) pulses was evaluated in 27 distinct acoustic parameter sets at low peak-rarefactional pressures (0.51 MPa or lower). The left hippocampus and lateral thalamus were noninvasively sonicated after administration of Definity microbubbles. Disruption of the BBB was confirmed by delivery of fluorescently tagged 3-, 10-, or 70-kDa dextrans. Under some conditions, dextrans were distributed homogeneously throughout the targeted region and accumulated at specific hippocampal landmarks and neuronal cells and axons. No histological damage was observed at the most effective parameter set. Our results have broadened the design space of parameters toward a wider safety window that may also increase vascular permeability. The study also uncovered a set of parameters that enhances the dose and distribution of molecular delivery, overcoming standard trade-offs in avoiding associated damage. Given the short pulses used similar to diagnostic ultrasound, new critical parameters were also elucidated to clearly separate therapeutic ultrasound from disruption-free diagnostic ultrasound.

Imaging the electromechanical activity of the heart in vivo.

Cardiac conduction abnormalities remain a major cause of death and disability worldwide. However, as of today, there is no standard clinical imaging modality that can noninvasively provide maps of the electrical activation. In this paper, electromechanical wave imaging (EWI), a novel ultrasound-based imaging method, is shown to be capable of mapping the electromechanics of all four cardiac chambers at high temporal and spatial resolutions and a precision previously unobtainable in a full cardiac view in both animals and humans. The transient deformations resulting from the electrical activation of the myocardium were mapped in 2D and combined in 3D biplane ventricular views. EWI maps were acquired during five distinct conduction configurations and were found to be closely correlated to the electrical activation sequences. EWI in humans was shown to be feasible and capable of depicting the normal electromechanical activation sequence of both atria and ventricles. This validation of EWI as a direct, noninvasive, and highly translational approach underlines its potential to serve as a unique imaging tool for the early detection, diagnosis, and treatment monitoring of arrhythmias through ultrasound-based mapping of the transmural electromechanical activation sequence reliably at the point of care, and in real time.

Feasibility of Phase Velocity Imaging Using Multi Frequency Oscillation-Shear Wave Elastography.

OBJECTIVE: To assess viscoelasticity, a pathologically relevant biomarker, shear wave elastography (SWE) generally uses phase velocity (PV) dispersion relationship generated via pulsed acoustic radiation force (ARF) excitation pulse. In this study, a multi-frequency oscillation (MFO)- excitation pulse with higher weight to higher frequencies is proposed to generate PV images via the generation of motion with energy concentrated at the target frequencies in contrast to the broadband frequency motion generated in pulsed SWE (PSWE). METHODS: The feasibility of MFO-SWE to generate PV images at 100 to 1000 Hz in steps of 100 Hz was investigated by imaging 6 and 70 kPa inclusions with 6.5 and 10.4 mm diameter and ex vivo bovine liver with and without the presence of an aberration layer and chicken muscle ex vivo, and 4T1 mouse breast tumor, in vivo with comparisons to PSWE. RESULTS: MFO-SWE-derived CNR was statistically higher than PSWE for 6 kPa (both with and without aberration) and 70 kPa (with aberration) inclusions and derived SNR of the liver was statistically higher than PSWE at higher frequency (600-1000 Hz). Quantitatively, at 600-1000 Hz, MFO-SWE improved CNR of inclusions (without and with) aberration on an average by (8.2 and 156)% and of the tumor by 122%, respectively, and improved SNR of the liver (without and with) aberration by (20.2 and 51.5)% and of chicken muscle by 72%, respectively compared to the PSWE. CONCLUSIONS AND SIGNIFICANCE: These results indicate the advantages of MFO-SWE to improve PV estimation at higher frequencies which could improve viscoelasticity quantification and feature delineation.

Polyvinyl Alcohol Phantoms With Heterogeneous Plaques: Estimation of Pulse Wave Velocity at the Stenotic Region Using Pulse Wave Imaging.

OBJECTIVE: Plaque characterization is essential for stroke prevention. In the study reported herein, we describe a heterogeneous phantom manufacturing technique with varying plaque compositions of different stiffness using polyvinyl alcohol (PVA) to emulate stenotic arteries and evaluated the use of pulse wave imaging (PWI) to assess plaque stiffness by comparing derived pulse wave velocities, with the goal of assessing plaque vulnerability and identifying high-risk patients for stroke. METHODS: Five stenotic phantoms (50% stenosis) were fabricated by pouring PVA solutions into 3-D-printed molds. Two of the phantoms had heterogeneous plaque compositions of soft (E0 = 13 kPa) and intermediate (E0 = 40 kPa) materials and of stiff (E0 = 54 kPa) and intermediate materials. Ultrasound sequences were acquired as the arterial phantoms were connected to a pulsating pump, and PWI was performed on the ultrasound acquisition using normalized cross-correlation to track the pulse-induced phantom wall distension propagations. Pulse wave velocities were estimated by fitting a linear regression line between the arrival time of the peak acceleration of the wall distension waveform and the corresponding location. RESULTS: Arterial phantoms with heterogeneous plaque stiffness were successfully fabricated. Pulse wave velocities of 2.06, 2.21, 2.49, 2.67 and 3.31 m/s were found in the phantom experiments using PWI for homogeneous soft plaque, the heterogeneous soft and intermediate plaque, homogeneous intermediate plaque, the heterogeneous stiff and intermediate plaque and homogeneous stiff plaque, respectively. CONCLUSION: A novel arterial phantom building technique was reported with varying heterogenous plaque compositions of different stiffness. The feasibility of using PWI to evaluate plaque stiffness in stenotic arteries was determined and found that PWI can distinguish between plaques of distinct stiffness and composition.

An all-ultrasound cranial imaging method to establish the relationship between cranial FUS incidence angle and transcranial attenuation in non-human primates in 3D.

Focused ultrasound (FUS) is a non-invasive and non-ionizing technique which deploys ultrasound waves to induce bio-effects. When paired with acoustically active particles such as microbubbles (MBs), it can open the blood brain barrier (BBB) to facilitate drug delivery otherwise inhibited due to the presence of BBB. One of the parameters that affects the FUS beam propagation is the beam incidence angle on the skull. Prior work by our group has shown that, as incidence angles deviate from 90°, FUS focal pressures attenuate and result in a smaller BBB opening volume. The incidence angles calculated in our prior studies were in 2D and used skull information from CT. The study presented herein develops methods to calculate incidence angle in 3D in non-human primate (NHP) skull fragments using harmonic ultrasound imaging without using ionizing radiation. Our results show that ultrasound harmonic imaging is capable of accurately depicting features such as sutures and eye-sockets of the skull. Furthermore, we were able to reproduce previously reported relationships between the incidence angle and FUS beam attenuation. We also show feasibility of performing ultrasound harmonic imaging in in-vivo non-human primates. The all-ultrasound method presented herein combined with our neuronavigation system stands to increase more widespread adoption of FUS and render it accessible by eliminating the need for CT cranial mapping.

Optimization of the Tracking Beam Sequence in Harmonic Motion Imaging.

Harmonic motion imaging (HMI) is an ultrasound elastography technique that estimates the viscoelastic properties of tissues by inducing localized oscillatory motion using focused ultrasound (FUS). The resulting displacement, assumed to be inversely proportional to the tissue local stiffness, is estimated using an imaging array based on RF speckle tracking. In conventional HMI, this is accomplished with plane-wave (PW) imaging, which inherently suffers from low lateral resolution. Coherent PW compounding (PWC) leverages spatial and temporal resolution using synthetic focusing in transmit. In this study, we introduced focused imaging with parallel tracking in HMI and compared parallel tracking of various transmit F-numbers (F/2.6, 3, 4, and 5) qualitatively and quantitatively with PW and PWC imaging at various compounded angle ranges (6°, 12°, and 18°). An in silico model of a 56-kPa spherical inclusion (diameter: 3.6 mm) embedded in a 5.3-kPa background and a 5.3-kPa elastic phantom with cylindrical inclusions (Young's moduli: 22-56 kPa, diameters: 2.0-8.6 mm) were imaged to assess different tracking beam sequences. Speckle biasing in displacement estimation associated with parallel tracking was also investigated and concluded to be negligible in HMI. Parallel tracking in receive (Rx) resulted in 2%-7% and 8%-12% increase compared to PW imaging ( ) in HMI contrast and contrast-to-noise ratio in silico and phantoms. Focused imaging with parallel tracking in Rx was concluded to be most robust among PW and PWC imaging for displacement estimation, and its preclinical feasibility was demonstrated in postsurgical human cancerous breast tissue specimens and in vivo murine models of breast cancer.

Functional ultrasound (fUS) imaging of displacement-guided focused ultrasound (FUS) neuromodulation in mice.

Focused ultrasound (FUS) stimulation is a promising neuromodulation technique with the merits of non-invasiveness, high spatial resolution, and deep penetration depth. However, simultaneous imaging of FUS-induced brain tissue displacement and the subsequent effect of FUS stimulation on brain hemodynamics has proven challenging thus far. In addition, earlier studies lack in situ confirmation of targeting except for the magnetic resonance imaging-guided FUS system-based studies. The purpose of this study is 1) to introduce a fully ultrasonic approach to in situ target, modulate neuronal activity, and monitor the resultant neuromodulation effect by respectively leveraging displacement imaging, FUS, and functional ultrasound (fUS) imaging, and 2) to investigate FUS-evoked cerebral blood volume (CBV) response and the relationship between CBV and displacement. We performed displacement imaging on craniotomized mice to confirm the in targeting for neuromodulation site. We recorded hemodynamic responses evoked by FUS and fUS revealed an ipsilateral CBV increase that peaks at 4 s post-FUS. We saw a stronger hemodynamic activation in the subcortical region than cortical, showing good agreement with the brain elasticity map that can also be obtained using a similar methodology. We observed dose-dependent CBV response with peak CBV, activated area, and correlation coefficient increasing with ultrasonic dose. Furthermore, by mapping displacement and hemodynamic activation, we found that displacement colocalizes and linearly correlates with CBV increase. The findings presented herein demonstrated that FUS evokes ipsilateral hemodynamic activation in cortical and subcortical depths and the evoked hemodynamic responses colocalized and correlate with FUS-induced displacement. We anticipate that our findings will help consolidate accurate targeting as well as an understanding of how FUS displaces brain tissue and affects cerebral hemodynamics.

Feasibility of Hologram-Assisted Bilateral Blood-Brain Barrier Opening in Non-Human Primates.

Focused ultrasound (FUS) and microbubbles facilitate blood-brain barrier opening (BBBO) noninvasively, transiently, and safely for targeted drug delivery. Unlike state-of-the-art approaches, in this study, we demonstrate for the first time the simultaneous, bilateral BBBO in non-human primates (NHPs) using acoustic holograms at caudate and putamen structures. The simple and low-cost system with a single-element FUS transducer and 3-D printed acoustic hologram was guided by neuronavigation and a robotic arm. The advantages of holograms are transcranial aberration correction, simultaneous multifocus and high localization, and target-independent transducer positioning, defining a promising alternative for time- and cost-efficient FUS procedures. Holograms were designed with the k-space method by time-reversal techniques. T1-weighted MRI was used for treatment planning, while the computed tomography (CT) scan provided the head tissues acoustic properties. For the BBBO procedure, a robotic arm allowed transducer positioning errors below 0.1 mm and 0.1°. Following positioning, 0.5-0.6-MPa, 513-kHz microbubble-enhanced FUS was applied for 4 min. For BBBO assessment, Post-FUS T1-weighted MRI was acquired, and contrast enhancement indicated bilateral gadolinium extravasation at both caudate or putamen structures. The two BBBO locations were separated by 13.13 mm with a volume of 91.81 mm3 in the caudate, compared with 9.40 mm with a volume of 124.52 mm3 in simulation, while they were separated by 21.74 mm with a volume of 145.38 mm3 in the putamen and compared with 22.32 mm with a volume of 156.42 mm3 in simulation. No neurological damage was observed through T2-weighted and susceptibility-weighted imaging. This study demonstrates the feasibility and safety of hologram-assisted neuronavigation-guided-FUS for BBBO in NHP, providing thus an avenue for clinical translation.

Amplitude-Modulation Frequency Optimization for Enhancing Harmonic Motion Imaging Performance of Breast Tumors in the Clinic.

OBJECTIVE: Elastography images tissue mechanical responses and infers the underlying properties to aid diagnosis and treatment response monitoring. The estimation of absolute or relative tumor properties may vary with dimensions even when the mechanical properties remain constant. Harmonic motion imaging (HMI) uses amplitude-modulated (AM) focused ultrasound to interrogate the targeted tissue's viscoelastic properties. In this study, effects of AM frequencies on HMI were investigated in terms of inclusion relative stiffness and size estimation. METHODS: AM frequencies from 200 to 600 Hz in steps of 100 Hz were considered using a 5.3-kPa phantom with cylindrical inclusions (Young's modulus: 22, 31, 44, 56 kPa, and diameter: 4.8, 8.1, 13.6, 19.8 mm) to optimize the performance of HMI in characterizing tumors with the same mechanical properties and of different dimensions. RESULTS: Consistent displacement ratios (DRs) (17.5% variation) of the inclusion to background were obtained with 200-Hz AM for breast-tumor-mimicking inclusions albeit a suboptimal inclusion size estimation obtained. 400-Hz was otherwise used for small and low-contrast inclusions (4.8 mm, 22 or 31 kPa). A linear relationship (R2 = 0.9043) was found between the inverse DR at these frequencies and the Young's modulus ratio. 400 Hz obtained the most accurate inclusion size estimation with an overall estimation error on the lateral dimension of 0.5 mm. In vivo imaging of breast cancer patients (n = 5) was performed at 200 or 400 Hz. CONCLUSION: The results presented herein indicate that the HMI AM frequency could be optimized adaptively in cases of different applications, i.e., at 200 or 400 Hz, depending on whether aimed for consistent DR measurement for tumor response assessment or tumor margin delineation for surgical planning. HMI may thus be capable of predicting the pathologic endpoint of tumors in response to neoadjuvant chemotherapy (NACT) as early as 3 weeks into treatment.

Functional Cerebral Neurovascular Mapping During Focused Ultrasound Peripheral Neuromodulation of Neuropathic Pain.

BACKGROUND: Nociceptive pain is required for healthy function, yet, neuropathic pain (disease or injury) can be severely debilitating. Though a wide-array of treatment options are available, they are often systemic and/or invasive. As a promising neuromodulation treatment, Focused ultrasound (FUS) is a noninvasive and highly spatially-targeted technique shown to stimulate neural activity, yet, effects on pain signaling are currently unknown. OBJECTIVE: Develop and validate a method for studying FUS nerve stimulation modulation of pain-evoked neural responses in vivo. METHODS: We developed a high-resolution functional ultrasound (fUS) method capable of mapping cortical responses in healthy and neuropathic pain mice in response to FUS neuromodulation treatment. RESULTS: FUS-evoked hemodynamic responses are correlated with the intensity of peripheral neuromodulation. We confirm functional connectivity is altered in neuropathic mice and demonstrate that FUS can modulate neuropathic pain-evoked hemodynamics. CONCLUSIONS: The findings presented herein provides evidence for an FUS-based nerve pain method and validates the fUS technique developed for monitoring pain-evoked hemodynamics. SIGNIFICANCE: We anticipate that the findings presented herein describe a noninvasive and flexible nerve modulation technique for pain mitigation, furthering evidence for clinical translation.