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To rapidly image and localize the focus in MR-guided focused ultrasound (FUS) while maintaining a low ultrasound duty cycle to minimize tissue effects.MR-acoustic radiation force imaging (ARFI) is key to targeting FUS procedures such as neuromodulation, and works by encoding ultrasound-induced displacements into the phase of MR images. However, it can require long scan times to cover a volume of tissue, especially when minimizing the FUS dose during targeting is paramount. To simultaneously minimize scan time and the FUS duty cycle, a 2-min three-dimensional (3D) reduced-FOV spin echo ARFI scan with two-dimensional undersampling was implemented at 3T with a FUS duty cycle of 0.85%. The 3D k-space sampling scheme incorporated uniform undersampling in one phase-encoded axis and partial Fourier (PF) sampling in the other. The scan interleaved FUS-on and FUS-off data collection to improve displacement map quality via a joint low-rank image reconstruction. Experiments in agarose and graphite phantoms and living macaque brains for neuromodulation and blood-brain barrier opening studied the effects of the sampling and reconstruction strategy on the acquisition, and evaluated its repeatability and accuracy.In the phantom, the distances between displacement centroids of 10 prospective reconstructions and a fully sampled reference were below 1 mm. In in vivo brain, the distances between centroids ranged from 1.3 to 2.1 mm. Results in phantom and in vivo brain both showed that the proposed method can recover the FUS focus compared to slower fully sampled scans.The proposed 3D MR-ARFI reduced-FOV method enables rapid imaging of the FUS focus while maintaining a low FUS duty cycle.

Critical limb ischemia (CLI) occurs when blood flow is restricted through the arteries, resulting in ulcers, necrosis, and chronic wounds in the downstream extremities. The development of collateral arterioles (i.e. arteriogenesis), either by remodeling of pre-existing vascular networks orde novogrowth of new vessels, can prevent or reverse ischemic damage, but it remains challenging to stimulate collateral arteriole development in a therapeutic context. Here, we show that a gelatin-based hydrogel, devoid of growth factors or encapsulated cells, promotes arteriogenesis and attenuates tissue damage in a murine CLI model. The gelatin hydrogel is functionalized with a peptide derived from the extracellular epitope of Type 1 cadherins. Mechanistically, these “GelCad” hydrogels promote arteriogenesis by recruiting smooth muscle cells to vessel structures in bothex vivoandin vivoassays. In a murine femoral artery ligation model of CLI, delivery ofin situcrosslinking GelCad hydrogels was sufficient to restore limb perfusion and maintain tissue health for 14 days, whereas mice treated with gelatin hydrogels had extensive necrosis and autoamputated within 7 days. A small cohort of mice receiving the GelCad hydrogels were aged out to 5 months and exhibited no decline in tissue quality, indicating durability of the collateral arteriole networks. Overall, given the simplicity and off-the-shelf format of the GelCad hydrogel platform, we suggest it could have utility for CLI treatment and potentially other indications that would benefit from arteriole development.

Phase-change contrast agents (PCCAs) consisting of lipid-encapsulated low-boiling point perfluorocarbons can be used in conjunction with ultrasound for diagnostic and therapeutic applications. One benefit of PCCAs is site-specific activation, whereby the liquid core is acoustically vaporized into a bubble detectable via ultrasound imaging. For further evaluation of PCCAs in a variety of applications, it is useful to disperse these nanodroplets into an acoustically compatible stationary matrix. However, many traditional phantom preparations require heating, which causes premature thermal activation of low-boiling point PCCAs. Polyvinyl alcohol (PVA) cryogels do not require heat to set. Here we propose a simple method for the incorporation of the low-boiling point PCCAs utilizing octafluoropropane (OFP) and decafluorbutane (DFB) into PVA cryogels for a variety of acoustic characterization applications. We then demonstrate the utility of the phantoms by activating droplets with a focused transducer, visualizing the lesions with ultrasound imaging. At 1 MHz, consistent droplet activation was consistently observed at 2.0 MPa and 4.0 MPa for OFP and DFB respectively.

Focused ultrasound blood-brain barrier (BBB) opening is a promising tool for targeted delivery of therapeutic agents into the brain. The volume of opening determines the extent of therapeutic administration and sets a lower bound on the size of targets which can be selectively treated. We tested a custom 1 MHz array transducer optimized for cortical regions in the macaque brain with the goal of achieving small volume openings. We integrated this device into a magnetic resonance image guided focused ultrasound system and demonstrated twelve instances of small volume BBB opening with average opening volumes of 59 ± 37 mm3and 184 ± 2 mm3in cortical and subcortical targets, respectively. We developed real-time cavitation monitoring using a passive cavitation detector embedded in the array and characterized its performance on a bench-top flow phantom mimicking transcranial BBB opening procedures. We monitored cavitation duringin-vivoprocedures and compared cavitation metrics against opening volumes and safety outcomes measured with FLAIR and susceptibility weighted MR imaging. Our findings show small BBB opening at cortical targets in macaques and characterize the safe pressure range for 1 MHz BBB opening. Additionally, we used subject-specific simulations to investigate variance in measured opening volumes and found high correlation (R2= 0.8577) between simulation predictions and observed measurements. Simulations suggest the threshold for 1 MHz BBB opening was 0.53 MPa. This system enables BBB opening for drug delivery and gene therapy to be targeted to more specific brain regions.

Contains fulltext : 290343.pdf (Publisher’s version ) (Open Access) Transcranial ultrasound stimulation (TUS) has been shown to be a safe and effective technique for non-invasive superficial and deep brain stimulation. Safe and efficient translation to humans requires estimating the acoustic attenuation of the human skull. Nevertheless, there are no international guidelines for estimating the impact of the skull bone. A tissue independent, arbitrary derating was developed by the U.S. Food and Drug Administration to take into account tissue absorption (0.3 dB/cm-MHz) for diagnostic ultrasound. However, for the case of transcranial ultrasound imaging, the FDA model does not take into account the insertion loss induced by the skull bone, nor the absorption by brain tissue. Therefore, the estimated absorption is overly conservative which could potentially limit TUS applications if the same guidelines were to be adopted. Here we propose a three-layer model including bone absorption to calculate the maximum pressure transmission through the human skull for frequencies ranging between 100 kHz and 1.5 MHz. The calculated pressure transmission decreases with the frequency and the thickness of the bone, with peaks for each thickness corresponding to a multiple of half the wavelength. The 95th percentile maximum transmission was calculated over the accessible surface of 20 human skulls for 12 typical diameters of the ultrasound beam on the skull surface, and varies between 40% and 78%. To facilitate the safe adjustment of the acoustic pressure for short ultrasound pulses, such as transcranial imaging or transcranial ultrasound stimulation, a table summarizes the maximum pressure transmission for each ultrasound beam diameter and each frequency. 8 p.

Transcranial focused ultrasound (FUS) stimulation under MRI guidance, coupled with functional MRI (fMRI) monitoring of effects, offers a precise, noninvasive technology to dissect functional brain circuits and to modulate altered brain functional networks in neurological and psychiatric disorders. Here we show that ultrasound at moderate intensities modulated neural activity bi-directionally. Concurrent sonication of somatosensory areas 3a/3b with 250 kHz FUS suppressed the fMRI signals produced there by peripheral tactile stimulation, while at the same time eliciting fMRI activation at inter-connected, off-target brain regions. Direct FUS stimulation of the cortex resulted in different degrees of BOLD signal changes across all five off-target regions, indicating that its modulatory effects on active and resting neurons differed. This is the first demonstration of the dual suppressive and excitative modulations of FUS on a specific functional circuit and of ability of concurrent FUS and MRI to evaluate causal interactions between functional circuits with neuron-class selectivity.

Anterior cingulate cortex (ACC) and striatum (STR) contain neurons encoding not only the expected values of actions, but also the value of stimulus features irrespective of actions. Values about stimulus features in ACC or STR might contribute to adaptive behavior by guiding fixational information sampling and biasing choices toward relevant objects, but they might also have indirect motivational functions by enabling subjects to estimate the value of putting effort into choosing objects. Here, we tested these possibilities by modulating neuronal activity in ACC and STR of nonhuman primates using transcranial ultrasound stimulation while subjects learned the relevance of objects in situations with varying motivational and cognitive demands. Motivational demand was indexed by varying gains and losses during learning, while cognitive demand was varied by increasing the uncertainty about which object features could be relevant during learning. We found that ultrasound stimulation of the ACC, but not the STR, reduced learning efficiency and prolonged information sampling when the task required averting losses and motivational demands were high. Reduced learning efficiency was particularly evident at higher cognitive demands and when subjects experienced loss of already attained tokens. These results suggest that the ACC supports flexible learning of feature values when loss experiences impose a motivational challenge and when uncertainty about the relevance of objects is high. Taken together, these findings provide causal evidence that the ACC facilitates resource allocation and improves visual information sampling during adaptive behavior.

Localizing the focus during transcranial focused ultrasound procedures is important to ensure accurate targeting of specific brain regions and interpretation of results. Magnetic resonance acoustic radiation force imaging uses the displacement induced by the ultrasound focus in the brain to localize the beam, but the high pressure required to displace brain tissue may cause damage or confounds during subsequent neuromodulatory experiments. Here, reduced apertures were applied to a phased array transducer to generate comparable displacement to the full aperture but with 20% lower free field pressure.

We designed, fabricated, and characterized a patient-specific, 3D-printed, stereotactic frame for repeated transcranial focused ultrasound (FUS) neuromodulation. The frame is compact, with minimal footprint, and can be removed and re-secured between treatments. The use of small skull anchor screws allows for the precise and repeatable transcranial FUS treatment without the need for MR-guidance following the initial calibration scan. Focus localization and repeatability were assessed via MR-thermometry on a macaque skull-phantom model. Focal localization, registration, steering, and re-steering was accomplished during the initial MRI calibration scan session. Keeping the steering coordinate constant in subsequent therapy and imaging sessions, we found good agreement between the steered foci and intended target, with target registration error of 0. 7 ± 0.3 and 0.7 ± 0.6mm (n = 4) in lateral and axial dimension, respectively. Focus position (steered and non-steered) was consistent, with sub-mm variation in each dimension between studies. Our preliminary studies show that our 3D printed, patient-specific stereotactic frame can reliably position and orient the ultrasound transducer for repeated targeting of brain regions without the need for MR-guidance. This compact frame will make continued transcranial FUS treatments financially and logistically more accessible to patients.

Accurate targeting is paramount for transcranial ultrasound procedures. Here we describe a new method for targeting transcranial ultrasound dubbed acoustic signature which uses acoustic feedback from a target's unique reflection patterns to guide the transducer to a previously defined orientation. We characterize the uniqueness and convergence of acoustic signatures on a macaque head phantom. We demonstrate submillimeter targeting accuracy using acoustic signature feedback with two transcranial ultrasound mechanical systems. This method provides an accurate and repeatable method for therapeutic transducer array placement.

Focused ultrasound (FUS) can concentrate energy noninvasively through the skull to elicit neuromodulation. Although the natural response of neurons to ultrasound has been explored, acoustically active drug loaded nanoparticles have the benefit of yielding a pharmacological response that may be more predictable than the effects of FUS alone. Researchers have developed drug delivery vehicles that release small molecule neuromodulatory drugs without opening blood brain barrier. It is desirable to increase drug release, and drug release typically increases with increased peak negative pressure (PNP). However, the likelihood of undesirable bioeffects, such as cavitation-induced focal hemorrhages increases with increasing PNP. Here, we examined echoes from propofol-containing nanoparticles during ultrasound exposures known to uncage propofol from the vehicle. Our goals were to 1) increase drug release without generating cavitation and 2) identify echoes that may be related to propofol release.

Even simple behaviors arise from the simultaneous activation of multiple regions in the brain. Thus, the ability to simultaneously stimulate multiple regions within a brain circuit should allow for better modulation of function. However, performing simultaneous multifocus ultrasound neuromodulation introduces challenges to transducer design. Using 3-D Fullwave simulations, we have designed an ultrasound neuromodulation array for nonhuman primates that: 1) can simultaneously focus on multiple targets and 2) include an imaging aperture for additional functional imaging. This design is based on a spherical array, with 128 15-mm elements distributed in a spherical helix pattern. It is shown that clustering the elements tightly around the 65-mm imaging aperture located at the top of the array improves targeting at shallow depths, near the skull surface. Spherical arrays have good focusing capabilities through the skull at the center of the array, but focusing on off-center locations is more challenging due to the natural geometric configuration and the angle of incidence with the skull. In order to mitigate this, the 64 elements closest to the aperture were rotated toward and focusing on a shallow target, and the 64 elements farthest from the aperture were rotated toward and focusing on a deeper target. Data illustrated that this array produced focusing on the somatosensory cortex with a gain of 4.38 and to the thalamus with a gain of 3.82. To improve upon this, the array placement was optimized based on phase aberration simulations, allowing for the elements with the largest impact on the gain at each focal point to be found. This optimization resulted in an array design that can focus on the somatosensory cortex with a gain of 5.19 and the thalamus with a gain of 4.45. Simulations were also performed to evaluate the ability of the array to focus on 28 additional brain regions, showing that off-center target regions can be stimulated, but those closer to the skull will require corrective steps to deliver the same amount of energy to those locations. This simulation and design process can be adapted to an individual monkey or human skull morphologies and specific target locations within individuals by using orientable 3-D printing of the transducer case and by electronic phase aberration correction.

Neuronal subgroups in anterior cingulate cortex (ACC) and the anterior striatum (STR) encode the reward structure of a given environment. But whether or how this reward information is used to guide information sampling, optimize decision making, or motivate behavior in cognitively challenging situations has remained elusive. Here, we causally tested these scenarios by transiently disrupting ACC and STR of rhesus monkeys with transcranial ultrasound with a learning task that independently varied cognitive and motivational demands. We found that disrupting the ACC, but not the STR, prolonged information sampling and reduced learning efficiency whenever the motivational payoff was low. These impairments were most pronounced at high cognitive demands and based on an inability to use loss experiences to improve performance. These results provide causal evidence that the ACC is necessary for motivation, to overcome anticipated costs from negative (loss) outcomes, and for cognition, to enhance visual information sampling during adaptive behavior.HIGHLIGHTSTranscranial ultrasound stimulation of the anterior cingulate cortex disrupts learning after loss experience.The ultrasound-induced learning deficit is exacerbated at high cognitive load.The ultrasound-induced learning deficit is accompanied by inefficient fixational information sampling.Anterior cingulate cortex causally supports credit assignment of aversive outcomes to visual features.

The aim of this study was to improve the sensitivity of magnetic resonance-acoustic radiation force imaging (MR-ARFI) to minimize pressures required to localize focused ultrasound (FUS) beams, and to establish safe FUS localization parameters for ongoing ultrasound neuromodulation experiments in living non-human primates. We developed an optical tracking method to ensure that the MR-ARFI motion-encoding gradients (MEGs) were aligned with a single-element FUS transducer and that the imaged slice was prescribed at the optically tracked location of the acoustic focus. This method was validated in phantoms, which showed that MR-ARFI-derived displacement sensitivity is maximized when the MR-ARFI MEGs were maximally aligned with the FUS propagation direction. The method was then applied in vivo to acquire displacement images in two healthy macaque monkeys (M fascicularis) which showed the FUS beam within the brain. Temperature images were acquired using MR thermometry to provide an estimate of in vivo brain temperature changes during MR-ARFI, and pressure and thermal simulations of the acoustic pulses were performed using the k-Wave package which showed no significant heating at the focus of the FUS beam. The methods presented here will benefit the multitude of transcranial FUS applications as well as future human applications.

PURPOSE: Transcranial focused ultrasound (FUS) is increasingly being explored to modulate neuronal activity. To target neuromodulation, researchers often localize the FUS beam onto the brain region(s) of interest using spatially tracked tools overlaid on pre-acquired images. Here, we quantify the accuracy of optically tracked image-guided FUS with magnetic resonance imaging (MRI) thermometry, evaluate sources of error, and demonstrate feasibility of these procedures to target the macaque somatosensory region. METHODS: We developed an optically tracked FUS system capable of projecting the transducer focus onto a pre-acquired MRI volume. To measure the target registration error (TRE), we aimed the transducer focus at a desired target in a phantom under image guidance, heated the target while imaging with MR thermometry, and then calculated the TRE as the difference between the targeted and heated locations. Multiple targets were measured using either an unbiased or bias-corrected calibration. We then targeted the macaque S1 brain region, where displacement induced by the acoustic radiation force was measured using MR acoustic radiation force imaging (MR-ARFI). RESULTS: All calibration methods enabled registration with TRE on the order of 3mm. Unbiased calibration resulted in an average TRE of 3.26 mm (min – max: 2.80 – 4.53 mm), which was not significantly changed by prospective bias correction (TRE of 3.05 mm; 2.06 – 3.81 mm, p=0.55). Restricting motion between the transducer and target and increasing the distance between tracked markers reduced the TRE to 2.43 mm (min-max: 0.79 – 3.88 mm). MR-ARFI images showed qualitatively similar shape and extent as projected beam profiles in a living non-human primate. CONCLUSIONS: Our study describes methods for image guidance of FUS neuromodulation and quantifies errors associated with this method in a large animal. The workflow is efficient enough for in vivo use, and we demonstrate transcranial MR-ARFI in vivo in macaques for the first time.

Accurate targeting is paramount for focused ultrasound (FUS) procedures. Here we describe a method for targeting FUS dubbed acoustic signature, which uses acoustic feedback from a target’s unique reflection patterns to guide the transducer to a previously defined orientation. We demonstrate convergence to the desired target in a 3 degree of freedom (DOF) water tank scenario and a 5 DOF robotic arm scenario. We also tested the acoustic signature technique for targeting with a phantom skull on a 3 DOF motor stage and a 5 DOF manual stereotactic frame designed for transcranial FUS procedures in an MRI environment. In both the water tank and the robotic arm convergence tests, the method converges to the target. The convergence was sufficiently smooth for automated gradient descent. In the 3-DOF test, the net targeting error was 0.30 ± 0.27 mm (n = 10). In the stereotactic frame 5-DOF test, the targeting error was 2.11 ± 0.99 mm and 3.2 ± 2.2° (n = 10) summed rotational error. The accuracy of this technique is limited by the positioning apparatus. This method may enable precise and repeatable FUS targeting for therapies which require multiple FUS sessions at the same target.

Therapeutic uses of transcranial focused ultrasound (tFUS) in the brain are being widely explored in both clinical and research settings from tissue destruction to blood brain barrier opening (BBBO) to neuromodulation. The appeal of tFUS is the ability to target structures throughout the brain with a millimeter scale focus. In order to understand the outcome of the treatment or experiment it is important to ensure the tFUS beam is targeted to and located at the region of interest. Image guidance allows for targeting of anatomical or functional structures within the brain. Here we present a targeting and localization scheme where optical tracking of the transducer is used to target the tFUS focus to a brain region within a previously acquired image and MR acoustic radiation force imaging is used to localize the beam in the brain to ensure the focus is at the target. By combining this targeting and localization scheme with a phased array transducer we are able to then steer the focus to ensure accurate sonications of specific brain regions using tFUS. This talk will discuss the application of this method to two different phased array transducers used for neuromodulation and BBBO in nonhuman primates.

Magnetic particle imaging (MPI) is a tracer-based imaging technique that does not require radiation or a cyclotron. However, it does require bulky MRI-like hardware and does not produce a background tissue image. We propose a new approach to MPI that uses the acoustic radiation force to dynamically move iron nanoparticles through a magnetic field gradient, thereby changing their magnetic moment and producing a detectable signal in a receiver coil. An image could be formed by electronically steering the ultrasound focus to push particles at different spatial locations, like an ultrasonic palpation. This would enable a device that attaches to an ultrasound imaging transducer for simultaneous MPI and inherently registered ultrasound imaging. To test the feasibility of the technique, a cylindrical agar and graphite phantom was placed between a Maxwell coil pair which generated a linear field gradient across it, and particle signals were detected using a receiver solenoid. 2-ms ultrasound pulses were applied using a 6 MHz transducer to generate displacements along the magnetic field gradient. Signal measurements confirmed a lack of signal when iron nanoparticles were absent from the phantom, but the signal was detected when particles were present, with amplitudes that linearly increased with the gradient coil current.

Focused ultrasound (FUS) is being explored for a variety of non-thermal transcranial applications, such as neuromodulation and blood-brain barrier opening. Although MRI is the gold standard for image guidance during FUS procedures, researchers are increasingly exploring other navigation methods, such as optical tracking, to guide ultrasound beam placement based on pre-acquired images for targeting outside the MRI setting. Current offline neuronavigation methods perform guidance based on the free-field ultrasound beam and do not incorporate attenuation and aberration effects of the skull. Here, we developed a pipeline that combines optical tracking and acoustic simulations to obtain accurate maps of the acoustic pressure within the skull.

Transcranial ultrasound is a noninvasive tool for brain therapies including ablation, neuromodulation, and blood-brain barrier opening. Sonication of cortical targets in macaques is challenging due to absorption and aberration from the skull. Because of this, transcranial ultrasound is largely limited to deep brain targets where the geometry of the skull is less prohibitive. Here, we address this limitation by designing a system which targets distal cortical regions and achieves a near free-field spot size at the target while minimizing pressure in the skull. We compare the focal volume and skull pressure performance with proximal sonication using two common therapeutic transducers and characterize the focal spot size at varied frequency while considering standing waves.

Local ablative treatment is a common intervention for cancers of soft tissues such as breast or liver, but they are invasive, requiring incision. High intensity focused ultrasound is being explored as an extracorporeal non-invasive option. This technology can be used to create a small focal spot of high pressures capable of thermally ablating targets as small as a grain of rice. However, this therapy carries a risk of off-target effects such as skin burns. Here, we describe a method that combines phase-shift nanodroplets (PSNDs) with multi-focus sonications to enhance volumetric ablation and ablation efficiencies while increasing the pre-focal temperatures by less than 6°C Furthermore, multi-focal ablation of 4 foci performed the best, generating a mean ablation volume of $120.2\pm 22.4\ \text{mm}^{3}$ and ablation efficiency of 0.04 mm3/J when compared to an ablation volume of $61.2\pm 21.16\text{mm}^{3}$ and ablation efficiency of 0.02 mm3/J in single foci case.

High intensity focused ultrasound (FUS) is a noninvasive technique for treatment of tissues that can lie deep within the body. There is a need for methods to rapidly and quantitatively map FUS pressure beams for quality assurance and accelerate development of FUS systems and techniques. However, conventional ultrasound pressure beam mapping instruments, including hydrophones and optical techniques, are slow, not portable, and expensive, and most cannot map beams at actual therapeutic pressure levels. Here, a rapid projection imaging method to quantitatively map FUS pressure beams based on continuous-wave background-oriented schlieren (CW-BOS) imaging is reported. The method requires only a water tank, a background pattern, and a camera and uses a multi-layer deep neural network to reconstruct two-dimensional root-mean-square (RMS) projected pressure maps that resolve the ultrasound propagation dimension and one lateral dimension. In this work, the method was applied to collect beam maps over a 3 × 1 cm(2) field-of-view with 0.425 mm resolution for focal pressures up to 9 MPa. Results at two frequencies and comparisons to hydrophone measurements show that CW-BOS imaging produces high-resolution quantitative RMS projected FUS pressure maps in under 10 s, the technique is linear and robust to beam rotations and translations, and it can map aberrated beams.

Ultrasound is gaining traction as a neuromodulation method due to its ability to remotely and non-invasively modulate neuronal activity with millimeter precision. However, there is little consensus about optimal ultrasound parameters required to elicit neuromodulation and how specific parameters drive mechanisms that underlie ultrasound neuromodulation. We address these questions in this work by performing a study to determine effective ultrasound parameters in a transgenic mouse brain slice model that enables calcium imaging as a quantitative readout of neuronal activity for ultrasound neuromodulation. We report that (1) calcium signaling increases with the application of ultrasound; (2) the neuronal response rate to ultrasound is dependent on pulse repetition frequency (PRF); and (3) ultrasound can reversibly alter the inhibitory effects of tetrodotoxin (TTX) in pharmacological studies. This study offers mechanistic insight into the PRF dependence of ultrasound neuromodulation and the nature of ultrasound/ion channel interaction.

Microbubble contrast agents are widely used in ultrasound imaging and therapy, typically with transmission center frequencies in the MHz range. Currently, an ultrasound center frequency near 250 kHz is proposed for clinical trials in which ultrasound combined with microbubble contrast agents is applied to open the blood brain barrier, since at this low frequency focusing through the human skull to a predetermined location can be performed with reduced distortion and attenuation compared to higher frequencies. However, the microbubble vibrational response has not yet been carefully evaluated at this low frequency (an order of magnitude below the resonance frequency of these contrast agents). In the past, it was assumed that encapsulated microbubble expansion is maximized near the resonance frequency and monotonically decreases with decreasing frequency. Our results indicated that microbubble expansion was enhanced for 250 kHz transmission as compared with the 1 MHz center frequency. Following 250 kHz insonation, microbubble expansion increased nonlinearly with increasing ultrasonic pressure, and was accurately predicted by either the modified Rayleigh–Plesset equation for a clean bubble or the Marmottant model of a lipid-shelled microbubble. The expansion ratio reached 30-fold with 250 kHz at a peak negative pressure of 400 kPa, as compared to a measured expansion ratio of 1.6 fold for 1 MHz transmission at a similar peak negative pressure. Further, the range of peak negative pressure yielding stable cavitation in vitro was narrow (~100 kPa) for the 250 kHz transmission frequency. Blood brain barrier opening using in vivo transcranial ultrasound in mice followed the same trend as the in vitro experiments, and the pressure range for safe and effective treatment was 75–150 kPa. For pressures above 150 kPa, inertial cavitation and hemorrhage occurred. Therefore, we conclude that (1) at this low frequency, and for the large oscillations, lipid-shelled microbubbles can be approximately modeled as clean gas microbubbles and (2) the development of safe and successful protocols for therapeutic delivery to the brain utilizing 250 kHz or a similar center frequency requires consideration of the narrow pressure window between stable and inertial cavitation.

Plane-wave ultrasound contrast imaging offers a faster, less destructive means for imaging microbubbles compared with traditional ultrasound imaging. Even though many of the most acoustically responsive microbubbles have resonant frequencies in the lower-megahertz range, higher frequencies (>3 MHz) have typically been employed to achieve high spatial resolution. In this work we implement and optimize low-frequency (1.5-4 MHz) plane-wave pulse inversion imaging on a commercial, phased-array imaging transducer in vitro and illustrate its use in vivo by imaging a mouse xenograft model. We found that the 1.8-MHz contrast signal was about four times that acquired at 3.1 MHz on matched probes and nine times greater than echoes received on a higher-frequency probe. Low-frequency imaging was also much more resilient to motion. In vivo, we could identify sub-millimeter vasculature inside a xenograft tumor model and easily assess microbubble half-life. Our results indicate that low-frequency imaging can provide better signal-to-noise because it generates stronger non-linear responses. Combined with high-speed plane-wave imaging, this method could open the door to super-resolution imaging at depth, while high power pulses could be used for image-guided therapeutics.

Thermal ablation by ultrasound is being explored as a local therapy for cancers of soft tissue, such as the liver or breast. One challenge for these treatments are off-target effects, including heating outside of the intended region or skin burns. Improvements in heating efficiency can mitigate these undesired outcomes, and here, we describe methods for using phase-shift nanodroplets (PSNDs) with multi-focus sonications to enhance volumetric ablation and ablation efficiency at constant powers while increasing the pre-focal temperature by less than 6 [Formula: see text]C. Multi-focus ablation with 4 foci performed the best and achieved a mean ablation volume of 120.2 ± 22.4 mm3 and ablation efficiency of 0.04 mm3 J-1 versus an ablation volume of 61.2 ± 21.16 mm3 and ablation efficiency of 0.02 mm3 J-1 in single focus case. The combined use of PSNDs with multi-focal ultrasound presented here is a new approach to increasing ablation efficiency while reducing off-target effects and could be generally applied in various focused ultrasound thermal ablation treatments.

Focused ultrasound (FUS) has gained recognition as a technique for non-invasive neuromodulation with high spatial precision and the ability to both excite and inhibit neural activity. Here we demonstrate that MRI-guided FUS is capable of exciting precise targets within areas 3a/3b in the monkey brain, causing downstream activations in off-target somatosensory and associated brain regions which are simultaneously detected by functional MRI. The similarity between natural tactile stimulation-and FUS- evoked fMRI activation patterns suggests that FUS likely can excite populations of neurons and produce associated spiking activities that may be subsequently transmitted to other functionally related touch regions. The across-region differences in fMRI signal changes relative to area 3a/3b between tactile and FUS conditions also indicate that FUS modulated the tactile network differently. The significantly faster rising (>1 sec) fMRI signals elicited by direct FUS stimulation at the targeted cortical region suggest that a different neural hemodynamic coupling mechanism may be involved in generating fMRI signals. This is the first demonstration of imaging neural excitation effects of FUS with BOLD fMRI on a specific functional circuit in non-human primates.

Transcranial focused ultrasound (FUS) is a non-invasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in non-human primates at 650kHz. The array is randomized with 128 elements, radius of curvature 7.2cm, and opening diameter 10.3cm (focal ratio 0.7). Simulations were used to optimize transducer geometry with respect to focus size, grating lobes, and directivity. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. A novel combination of optical tracking and acoustic mapping enabled measurement of the 3D pressure distribution in the cortical region of an ex vivo skull to within ~3.5 mm of the surface, and allowed accurate modelling of the experiment via non-homogeneous 3D acoustic simulations. The data demonstrates acoustic focusing beyond the skull bone, with the focus slightly broadened and shifted proximal to the skull. The fabricated design is capable of targeting regions within the S1 sensorimotor cortex of macaques., Pre-print

Running-related injuries (RRI) may result from accumulated microtrauma caused by combinations of high load magnitudes (vertical ground reaction forces; vGRFs) and numbers (strides). Yet relationships between vGRF and RRI remain unclear - potentially because previous research has largely been constrained to collecting vGRFs in laboratory settings and ignoring relationships between RRI and stride number. In this preliminary proof-of-concept study, we addressed these constraints: Over a 60-day period, each time collegiate athletes (n = 9) ran they wore a hip-mounted activity monitor that collected accelerations throughout the entire run. Accelerations were used to estimate peak vGRF, number of strides, and weighted cumulative loading (sum of peak vGRFs weighted to the 9th power) across the entirety of each run. Runners also reported their post-training pain/fatigue and any RRI that prevented training. Across 419 runs and >2.1 million strides, injured (n = 3) and uninjured (n = 6) participants did not report significantly different pain/fatigue (p = 0.56) or mean number of strides per run (p = 0.91). Injured participants did, however, have significantly greater peak vGRFs (p = 0.01) and weighted cumulative loading per run (p

Focused ultrasound is a promising method for non-invasive neural stimulation in the brain. Early studies have shown that neurological conditions such as essential tremors can be effectively treated with ultrasound ablation, while sub-thermal stimulation is being explored to probe functional connections in the brain and may have therapeutic benefits in a variety of neurological diseases. Although systems for transcranial ablation exist for human subjects, they are not optimized for cortical stimulation or studies in non-human primates. Here we report on the design and characterization of a new spherically-focused randomized sparse array transducer.

Non-invasive, quantitative methods to assess the properties of biological tissues are needed for many therapeutic and tissue engineering applications. Magnetic resonance elastography (MRE) has historically relied on external vibration to generate periodic shear waves. In order to focally assess a biomaterial or to monitor the response to ablative therapy, the interrogation of a specific region of interest by a focused beam is desirable and transient MRE (t-MRE) techniques have previously been developed to accomplish this goal. Also, strategies employing a series of discrete ultrasound pulses directed to increasing depths along a single line-of-sight have been designed to generate a quasi-planar shear wave. Such 'supersonic' excitations have been applied for ultrasound elasticity measurements. The resulting shear wave is higher in amplitude than that generated from a single excitation and the properties of the media are simply visualized and quantified due to the quasi-planar wave geometry and the opportunity to generate the wave at the site of interest. Here for the first time, we extend the application of supersonic methods by developing a protocol for supersonic transient magnetic resonance elastography (sst-MRE) using an MR-guided focused ultrasound system capable of therapeutic ablation. We apply the new protocol to quantify tissue elasticity in vitro using biologically-relevant inclusions and tissue-mimicking phantoms, compare the results with elasticity maps acquired with ultrasound shear wave elasticity imaging (US-SWEI), and validate both methods with mechanical testing. We found that a modified time-of-flight (TOF) method efficiently quantified shear modulus from sst-MRE data, and both the TOF and local inversion methods result in similar maps based on US-SWEI. With a three-pulse excitation, the proposed sst-MRE protocol was capable of visualizing quasi-planar shear waves propagating away from the excitation location and detecting differences in shear modulus of 1 kPa. The techniques demonstrated here have potential application in real-time in vivo lesion detection and monitoring, with particular significance for image-guided interventions.

Background Mild-hyperthermia therapy (40–45 °C) with high-intensity focused ultrasound (HIFU) is a technique being considered in a number of different treatments such as thermally activated drug delivery, immune-stimulation, and as a chemotherapy adjuvant. Mechanical damage and loss of cell viability associated with HIFU-induced acoustic cavitation may pose a risk during these treatments or may hinder their success. Here we present a method that achieves mild heating and reduces cavitation by using a multi-focused HIFU beam. We quantify cavitation level and temperature rise in multi-focal sonications and compare it to single-focus sonications at the transducer geometric focus. Methods Continuous wave sonications were performed with the Sonalleve V2 transducer in gel phantoms and pork at 5, 10, 20, 40, 60, 80 acoustic watts for 30 s. Cavitation activity was measured with two ultrasound (US) imaging probes, both by computing the raw channel variance and using passive acoustic mapping (PAM). Temperature rise was measured with MR thermometry at 3 T. Cavitation and heating were compared for single- and multi-focal sonication geometries. Multi-focal sonications used four points equally spaced on a ring of either 4 mm or 8 mm diameter. Single-focus sonications were not steered. Results Multi-focal sonication generated distinct foci that were visible in MRI thermal maps in both phantoms and pork, and visible in PAM images in phantoms only. Cavitation activity (measured by channel variance) and mean PAM image value were highly correlated (r > 0.9). In phantoms, cavitation exponentially decreased over the 30-second sonication, consistent with depletion of cavitation nuclei. In pork, sporadic spikes signaling cavitation were observed with single focusing only. In both materials, the widest beam reduced average and peak cavitation level by a factor of two or more at each power tested when compared to a single focus. The widest beam reduced peak temperature by at least 10 °C at powers above 5 W, and created heating that was more spatially diffuse than single focus, resulting in more voxels in the mild heating (3–8 °C) range. Conclusions Multi-focal HIFU can be used to achieve mild temperature elevation and reduce cavitation activity.

Ultrasound is a rapidly advancing field with many emerging diagnostic and therapeutic applications. For diagnostics, new vascular targets are routinely identified and mature technologies are being translated to humans, while other recent innovations may bring about the creation of acoustic reporter genes and micron-scale resolution with ultrasound. As a cancer therapy, ultrasound is being explored as an adjuvant to immune therapies and to deliver acoustically or thermally active drugs to tumor regions. Ultrasound-enhanced delivery across the blood brain barrier (BBB) could potentially be very impactful for brain cancers and neurodegenerative diseases where the BBB often impedes the delivery of therapeutic molecules. In this minireview, we provide an overview of these topics in the field of ultrasound that are especially relevant to the interests of World Molecular Imaging Society.

Our goal was to develop strategies to quantify the accumulation of model therapeutics in small brain metastases using multimodal imaging, in order to enhance the potential for successful treatment. Human melanoma cells were injected into the left cardiac ventricle of immunodeficient mice. Bioluminescent, MR and PET imaging were applied to evaluate the limits of detection and potential for contrast agent extravasation in small brain metastases. A pharmacokinetic model was applied to estimate vascular permeability. Bioluminescent imaging after injecting d-luciferin (molecular weight (MW) 320 D) suggested that tumor cell extravasation had already occurred at week 1, which was confirmed by histology. 7T T1w MRI at week 4 was able to detect non-leaky 100 μm sized lesions and leaky tumors with diameters down to 200 μm after contrast injection at week 5. PET imaging showed that (18)F-FLT (MW 244 Da) accumulated in the brain at week 4. Gadolinium-based MRI tracers (MW 559 Da and 2.066 kDa) extravasated after 5 weeks (tumor diameter 600 μm), and the lower MW agent cleared more rapidly from the tumor (mean apparent permeabilities 2.27 × 10(-5)cm/s versus 1.12 × 10(-5)cm/s). PET imaging further demonstrated tumor permeability to (64)Cu-BSA (MW 65.55 kDa) at week 6 (tumor diameter 700 μm). In conclusion, high field T1w MRI without contrast may improve the detection limit of small brain metastases, allowing for earlier diagnosis of patients, although the smallest lesions detected with T1w MRI were permeable only to d-luciferin and the amphipathic small molecule (18)F-FLT. Different-sized MR and PET contrast agents demonstrated the gradual increase in leakiness of the blood tumor barrier during metastatic progression, which could guide clinicians in choosing tailored treatment strategies.

Insulin resistance is frequently associated with hypertension and type 2 diabetes. The cytochrome P450 (CYP) arachidonic acid epoxygenases (CYP2C, CYP2J) and their epoxyeicosatrienoic acid (EET) products lower blood pressure and may also improve glucose homeostasis. However, the direct contribution of endogenous EET production on insulin sensitivity has not been previously investigated. In this study, we tested the hypothesis that endogenous CYP2C-derived EETs alter insulin sensitivity by analysing mice lacking CYP2C44, a major EET producing enzyme, and by testing the association of plasma EETs with insulin sensitivity in humans. We assessed insulin sensitivity in wild-type (WT) and Cyp2c44 −/− mice using hyperinsulinaemic–euglycaemic clamps and isolated skeletal muscle. Insulin secretory function was assessed using hyperglycaemic clamps and isolated islets. Vascular function was tested in isolated perfused mesenteric vessels. Insulin sensitivity and secretion were assessed in humans using frequently sampled intravenous glucose tolerance tests and plasma EETs were measured by mass spectrometry. Cyp2c44 −/− mice showed decreased glucose tolerance (639 ± 39.5 vs 808 ± 37.7 mmol/l × min for glucose tolerance tests, p = 0.004) and insulin sensitivity compared with WT controls (hyperinsulinaemic clamp glucose infusion rate average during terminal 30 min 0.22 ± 0.02 vs 0.33 ± 0.01 mmol kg−1 min−1 in WT and Cyp2c44 −/− mice respectively, p = 0.003). Although glucose uptake was diminished in Cyp2c44 −/− mice in vivo (gastrocnemius Rg 16.4 ± 2.0 vs 6.2 ± 1.7 μmol 100 g−1 min−1, p

INTRODUCTION Low intensity focused ultrasound has recently been identified as a novel method of stimulating targeted neurons. We hypothesized that ultrasound stimulation of the posterior tibial nerve would inhibit bladder contractions in an established rat model of rhythmic bladder contractions. METHODS Cyclical detrusor contractions were initiated by placing a transurethral catheter in female rats and infusing saline into the bladder. Transcutaneous ultrasound pulses were then delivered to the lower extremity of a rat (overlying the posterior tibial nerve) using a single element spherically focused 250 kHz transducer. Sixty-three cycles were repeated at 2 kHz for 300 ms at peak negative pressure of 900 kPa pulsed at 0.5 Hz. RESULTS We report successful suppression of bladder contractions using ultrasound stimulation in 10 animals. The average latency between the initiation of ultrasound and suppression of bladder contractions was 3 min 23 s (±51 s), the average time of contraction suppression was 13 min and 50 s (±2 min 25 s) and the average time from the end of ultrasound to return of contractions was 9 min 37 s (±2 min and 30 s). CONCLUSION In this work, we demonstrate the ability of targeted transcutaneous ultrasound to inhibit rhythmic bladder contractions in anesthetized rats. Due to its non-invasive nature and ease of application, we believe ultrasound mediated suppression of the micturition reflex is potentially an ideal outpatient treatment of overactive bladder and dysfunctional elimination.