Focused Ultrasound Sonication Research Articles

Focused ultrasound-enhanced intranasal brain delivery of brain-derived neurotrophic factor.

The objective of this study was to unveil the potential mechanism of focused ultrasound (FUS)-enhanced intranasal (IN) brain drug delivery and assess its feasibility in the delivery of therapeutic molecules. Delivery outcomes of fluorescently-labeled dextrans to mouse brains by IN administration either before or after FUS sonication were compared to evaluate whether FUS enhances IN delivery by active pumping or passive diffusion. Fluorescence imaging of brain slices found that IN administration followed by FUS sonication achieved significantly higher delivery than IN administration only, while pre-treatment by FUS sonication followed by IN administration was not significantly different from IN administration only. Brain-derived neurotrophic factor (BDNF), a promising neurotrophic factor for the treatment of many central nervous system diseases, was delivered by IN followed by FUS to demonstrate the feasibility of this technique and compared with the established FUS technique where drugs are injected intravenously. Immunohistochemistry staining of BDNF revealed that FUS-enhanced IN delivery achieved similar locally enhanced delivery as the established FUS technique. This study suggested that FUS enhances IN brain drug delivery by FUS-induced active pumping of the drug and demonstrated that FUS-enhanced IN delivery is a promising technique for noninvasive and localized delivery of therapeutic molecules to the brain.

Ultrasound/Magnetic Targeting with SPIO-DOX-Microbubble Complex for Image-Guided Drug Delivery in Brain Tumors.

One of the greatest challenges in the deployment of chemotherapeutic drugs against brain tumors is ensuring that sufficient drug concentrations reach the tumor, while minimizing drug accumulation at undesired sites. Recently, injection of therapeutic agents following blood-brain barrier (BBB) opening by focused ultrasound (FUS) with microbubbles (MBs) has been shown to enhance drug delivery in targeted brain regions. Nevertheless, the distribution and quantitative deposition of agents delivered to the brain are still hard to estimate. Based on our previous work on superparamagnetic iron oxide (SPIO)-loaded MBs, we present a novel theranostic complex of SPIO-Doxorubicin (DOX)-conjugated MB (SD-MB) for drug delivery to the brain. Magnetic labeling of the drug enables direct visualization via magnetic resonance imaging, and also facilitates magnetic targeting (MT) to actively enhance targeted deposition of the drug. In a rat glioma model, we demonstrated that FUS sonication can be used with SD-MBs to simultaneously facilitate BBB opening and allow dual ultrasound/magnetic targeting of chemotherapeutic agent (DOX) delivery. The accumulation of SD complex within brain tumors can be significantly enhanced by MT (25.7 fold of DOX, 7.6 fold of SPIO). The change in relaxation rate R2 (1/T2) within tumors was highly correlated with SD deposition as quantified by high performance liquid chromatography (R2 = 0.93) and inductively coupled plasma-atomic emission spectroscopy (R2 = 0.94), demonstrating real-time monitoring of DOX distribution. Our results suggest that SD-MBs can serve as multifunction agents to achieve advanced molecular theranostics.

Targeting microbubbles-carrying TGFβ1 inhibitor combined with ultrasound sonication induce BBB/BTB disruption to enhance nanomedicine treatment for brain tumors

The clinical application of chemotherapy for brain cancer tumors remains a challenge due to difficulties in the transport of therapeutic agents across the blood–brain barrier/blood–tumor barrier (BBB/BTB). In this study, we developed des-octanoyl ghrelin-conjugated microbubbles (GMB) loaded with TGFβ1 inhibitor (LY364947) (GMBL) to induce BBB/BTB disruption for ultrasound (US) sonication with GMBL. The in-vitro stability study showed that GMB was pretty stable over one month. The in-vivo study showed that the accumulation of superparamagnetic iron oxide nanoparticles (SPION) in the sonicated tumor was significantly higher for focused US sonication in the presence of GMBL, indicating that GMBL/US can locally disrupt BBB/BTB to promote vascular permeability of nanoparticles. In addition, the combination of folate-conjugated polymersomal doxorubicin (FPD) and GMBL/US (FPD+GMBL/US) achieved the best anti-glioma effect and significant improvement in the overall survival time for brain tumor-bearing mice. When combined with focused US, GMBL facilitated local BBB/BTB disruption and simultaneously released LY364947 to decrease the pericyte coverage of the endothelium at the targeted brain tumor sites, resulting in enhanced accumulation and antitumor activity of FPD. The overall results indicate that GMBL/US owns a great potential for non-invasive targeting delivery of nanomedicine across the BBB to treat central nervous system (CNS) diseases.

Focused ultrasound-mediated non-invasive brain stimulation: examination of sonication parameters.

Transcranial focused ultrasound (FUS) has emerged as a new brain stimulation modality. The range of sonication parameters for successful brain stimulation warrants further investigation. The objective of this study was to examine the range of FUS sonication parameters that minimize the acoustic intensity/energy deposition while successfully stimulating the motor brain area in Sprague-Dawley rats. We transcranially administered FUS to the somatomotor area of the rat brain and measured the acoustic intensity that caused excitatory effects with respect to different pulsing parameters (tone-burst duration, pulse-repetition frequency, duty cycle, and sonication duration) at 350 and 650kHz of fundamental frequency. We observed that motor responses were elicited at minimum threshold acoustic intensities (4.9-5.6W/cm(2) in spatial-peak pulse-average intensity; 2.5-2.8W/cm(2) in spatial-peak temporal-average intensity) in a limited range of sonication parameters, i.e. 1-5ms of tone-burst duration, 50% of duty cycle, and 300ms of sonication duration, at 350kHz fundamental frequency. We also found that the pulsed sonication elicited motor responses at lower acoustic intensities than its equivalent continuous sonication. Our results suggest that the pulsed application of FUS selectively stimulates specific brain areas-of-interest at an acoustic intensity that is compatible with regulatory safety limits on biological tissue, thus allowing for potential applications in neurotherapeutics.

Estimation of the spatial profile of neuromodulation and the temporal latency in motor responses induced by focused ultrasound brain stimulation

This study investigates the spatial profile and the temporal latency of the brain stimulation induced by the transcranial application of pulsed focused ultrasound (FUS). The site of neuromodulation was detected using 2-deoxy-2-[18F]fluoro-d-glucose PET immediately after FUS sonication on the unilateral thalamic area of Sprague–Dawley rats. The latency of the stimulation was estimated by measuring the time taken from the onset of the stimulation of the appropriate brain motor area to the corresponding tail motor response. The brain area showing elevated glucose uptake from the PET image was much smaller (56±10% in diameter, 24±6% in length) than the size of the acoustic focus, which is conventionally defined by the full-width at half-maximum of the acoustic intensity field. The spatial dimension of the FUS-mediated neuromodulatory area was more localized, approximated to be full-width at 90%-maximum of the acoustic intensity field. In addition, the time delay of motor responses elicited by the FUS sonication was 171±63 (SD) ms from the onset of sonication. When compared with latencies of other nonultrasonic neurostimulation techniques, the longer time delay associated with FUS-mediated motor responses is suggestive of the nonelectrical modes of neuromodulation, making it a distinctive brain stimulation method.

Delivery of different-size molecules by ultrasound-induced blood-brain barrier opening and its correlation with acoustic emission

Focused ultrasound (FUS) in combination with microbubbles (MBs) has been successfully used in the delivery of therapeutic agents of various sizes through the blood-brain barrier (BBB) in preclinical studies. However, the dependence of delivery efficiency on the drug molecular size calls for further exploration. Fluorescence-labeled dextrans of molecular weights of 3, 70, 150, and 2000 kDa were used as model therapeutic compounds. Dextrans were mixed with MBs and injected intravenously to mice immediately after the onset of FUS sonication. The acoustic emission from ultrasound-activated MBs was acquired passively using a 10 MHz transducer and quantified for stable, inertial, and total cavitation doses. The drug delivery efficiency was quantified by the relative delivery amount and volume estimated based on fluorescent images of the brains. It was found that dextran of 3 kDa can be delivered trans-BBB at a pressure level below the inertial cavitation threshold; however, dextrans of 70, 150, and 2000 kDa were delivered only when the pressure was above the inertial cavitation threshold. At the same pressure level, the amount and volume of dextrans delivered decreased as the dextran size increased. A linear correlation of total cavitation dose and the fluorescence enhancement was found for each size dextran.

Focused Ultrasound-Modulated Glomerular Ultrafiltration Assessed by Functional Changes in Renal Arteries

This study demonstrates the feasibility of using focused ultrasound (FUS) to modulate glomerular ultrafiltration by renal artery sonication and determine if protein-creatinine ratios are estimated through vascular parameters. All animal experiments were approved by our Animal Care and Use Committee. The renal arteries of Sprague-Dawley rats were surgically exposed and sonicated at various acoustic power levels using a FUS transducer with a resonant frequency of 1 MHz. The mean peak systolic velocity (PSV) of the blood flow was measured by Doppler ultrasound imaging. Urinary protein-creatinine ratios were calculated during the experiments. Histological examination of renal arteries and whole kidneys was performed. The PSV, pulsatility index, and resistance index of blood flow significantly increased in the arteries after FUS sonication without microbubbles (p<0.05). The change in normalized protein-creatinine ratios significantly increased with increasing acoustic power, but such was not observed when microbubbles were administered. Furthermore, no histological changes were observed in the hematoxylin- and eosin-stained sections. Glomerular ultrafiltration is regulated temporarily by renal artery sonication without microbubbles. Monitoring vascular parameters are useful in estimating the normalized change in protein-creatinine ratios.

Detection of Intracerebral Hemorrhage and Transient Blood-Supply Shortage in Focused-Ultrasound-Induced Blood–Brain Barrier Disruption by Ultrasound Imaging

Focused ultrasound (FUS) in the presence of microbubbles can selectively open the blood–brain barrier (BBB). However, since overexcitation by FUS probably induces intracerebral hemorrhage, it is essential to develop an imaging approach for real-time detection of hemorrhage and blood-flow changes during FUS-induced BBB disruption. Here we investigated the feasibility of using ultrasound imaging to monitor the transient responses of FUS-induced BBB disruption. The BBB was disrupted with in-house-manufactured microbubbles in rats by 1-MHz FUS with a pressure of 1.1 MPa (pulse repetition frequency: 1 Hz, pulse duration: 10 ms, exposure time: 60 s) and imaged for the next 2 h. Ultrasound B-mode imaging was used to detect hyperechoic changes induced by hemorrhage and contrast-enhanced ultrasound (US) imaging was performed to analyze changes in blood flow. Hyperechoic spots appeared in B-mode images at 5 s after FUS sonication and contrast-enhanced US images simultaneously showed a region of transient blood-supply shortage in the sonicated area. Thus, the location of hyperechoic spots correlated with hemorrhagic patterns and the blood-supply-shortage region was consistent with the BBB-disrupted areas. Furthermore, we detected a transient hyperemic response in the unsonicated contralateral hemisphere brain. Our approach has potential as an immediate-feedback control tool for preventing the induction of intracerebral hemorrhage during FUS treatment.

Enhancement of focused ultrasound with microbubbles on the treatments of anticancer nanodrug in mouse tumors

Ultrasound sonication with microbubbles (MBs) has the potential to enhance the delivery of nanoparticles into the sonicated tumors. In this study, we investigated the feasibility of focused ultrasound (FUS) sonication with MBs to improve nanodrug delivery and tumor treatment. Tumor-bearing mice were first injected with MBs (SonoVue) intravenously, were then sonicated at the tumors with FUS sonication, and were finally injected with the PEGylated liposomal doxorubicin (DOX). The accumulation of DOX in tumors with time, the tumor growth responses for initial treated tumor size and DOX dosage, and the response for an additional sonication after DOX injection were studied. The results demonstrate that FUS sonication with MBs can significantly enhance DOX accumulation in the sonicated tumor at 24 hours after treatment. A significant hindrance to tumor growth is achieved for a small tumor with a low dose, whereas large tumors require a higher dose. From the Clinical EditorIn this novel research study, focused ultrasound created microbubbles were utilized to enhance the delivery of PEGylated liposomal doxorubicin in a murine tumor model, demonstrating superior drug delivery compared to other methods. Focused ultrasound-based techniques are increasingly studied in cancer research, and this new observation will likely lead to additional investigations of different tumor lines, penetration depths and delivery vehicles.

Focused ultrasound modulates the level of cortical neurotransmitters: Potential as a new functional brain mapping technique

AbstractRegional modulation of the level of cortical neurotransmitters in the brain would serve as a new functional brain mapping technique to interrogate the neurochemical actions of the brain. We investigated the utility of the application of low‐intensity, pulsed sonication of focused ultrasound (FUS) to the brain to modulate the extracellular level of dopamine (DA) and serotonin (5‐HT). FUS was delivered to the thalamic areas of rats, and extracellular DA and 5‐HT were sampled from the frontal lobe using the microdialysis technique. The concentration changes of the sampled DA and 5‐HT were measured through high‐performance liquid chromatography. We observed a significant increase of the extracellular concentrations of DA and 5‐HT in the FUS‐treated group as compared with those in the unsonicated group. Our results provide the first direct evidence that FUS sonication alters the level of extracellular concentration of these monoamine neurotransmitters and has a potential modulatory effect on their local release, uptake, or degradation. Our findings suggest that the pulsed application of FUS offers new perspectives for a possible noninvasive modulation of neurotransmitters and may have diagnostic as well as therapeutic implications for DA/5‐HT‐mediated neurological and psychiatric disorders. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 232–240, 2011

Cell apoptosis and proliferation inhibition of pancreatic cancer induced by sub-threshold focused ultrasound (FUS)

To evaluate the effects of sub-threshold focused ultrasound (FUS) sonication on the pancreatic cancer cell. The human pancreatic carcinoma cell line PaTu 8988t suspension and pancreatic carcinoma xenograft in nude mice were sonicated by FUS using sub-threshold doses. The temperature at the focus was controlled at below 60°C. The cell apoptosis in vitro was tested by flow cytometer at 3, 6, 12, 24 and 48h after FUS sonication. Colony formation was used to evaluate the cell growth inhibition of FUS in vitro. The tumor volume of the xenograft was measured before and after FUS sonication. Then the slides of the tumor were under hematoxylin-eosin (H&E) staining and TdT-mediated dUTP nick end labeling (TUNEL) to evaluate the effect of FUS on pancreatic carcinoma xenograft in vivo. The maximum cell suspension temperature of the FUS sonication group was 55.8±2.17°C. The cell apoptosis rate peaked at 24h after FUS sonication, the differences between the FUS sonication group and control group were statistically significant (P<0.05). Colony formation rates were 50.40±3.81% for the control group and 26.82±2.88% for FUS sonication group (P<0.05). For the xenografts in nude mice, the mean tumor volumes of the control group and the FUS sonication group 15 days after sonication were 1746.58±312.77mm(3) and 1085.23±217.13mm(3) (P<0.05). H&E staining and TUNEL assay showed both necrotic and apoptotic cells. Sub-threshold FUS sonication could induce cell apoptosis and inhibit the proliferation of pancreatic cancer cells.

Focused ultrasound-mediated suppression of chemically-induced acute epileptic EEG activity.

BackgroundEpilepsy is a common neurological disorder, which is attributed to uncontrollable abnormal hyper-excitability of neurons. We investigated the feasibility of using low-intensity, pulsed radiation of focused ultrasound (FUS) to non-invasively suppress epileptic activity in an animal model (rat), which was induced by the intraperitonial injection of pentylenetetrazol (PTZ).ResultsAfter the onset of induced seizures, FUS was transcranially administered to the brain twice for three minutes each while undergoing electroencephalographic (EEG) monitoring. An air-backed, spherical segment ultrasound transducer (diameter: 6 cm; radius-of-curvature: 7 cm) operating at a fundamental frequency of 690 KHz was used to deliver a train of 0.5 msec-long pulses of sonication at a repetitive rate of 100 Hz to the thalamic areas of the brain. The acoustic intensity (130 mW/cm2) used in the experiment was sufficiently within the range of safety guidelines for the clinical ultrasound imaging. The occurrence of epileptic EEG bursts from epilepsy-induced rats significantly decreased after sonication when it was compared to the pre-sonication epileptic state. The PTZ-induced control group that did not receive any sonication showed a sustained number of epileptic EEG signal bursts. The animals that underwent sonication also showed less severe epileptic behavior, as assessed by the Racine score. Histological analysis confirmed that the sonication did not cause any damage to the brain tissue.ConclusionsThese results revealed that low-intensity, pulsed FUS sonication suppressed the number of epileptic signal bursts using acute epilepsy model in animal. Due to its non-invasiveness and spatial selectivity, FUS may offer new perspectives for a possible non-invasive treatment of epilepsy.

Reversible blood–brain barrier disruption by repeated transcranial focused ultrasound allows enhanced extravasation

The permeability of blood–brain barrier (BBB) for albumin can be enhanced by focused ultrasound (FUS) in a targeted region when this is applied in the presence of ultrasound contrast agent (UCA). In this study, we demonstrate that, using this noninvasive treatment, Evans Blue (EB) extravasation can be enhanced by repeated sonication. Sonications were applied at an ultrasound frequency of 1 MHz with a 5% duty cycle, and a repetition frequency of 1 Hz. The brains of male Sprague–Dawley rats were subjected to FUS exposure at the same targeted site. At the same acoustic power, the extravasation caused by leakage of EB into the brain was found to be dependent on the applied sonication time. In vivo, both single and repeated sonications increased the extravasation of the albumin binding EB, especially for the repeated sonication group. In the retreatment experiment, there was a nearly twofold increase in EB extravasation in groups with a second sonication compared with the single sonication group. BBB disruption can be prolonged by repeated FUS sonication and the duration is dependent on the time point of the resonication after the first sonication. Compared to a single sonication, the MR imaging analysis and histological examination of the affected brains indicated that the pattern of contrast enhancement was changed and that vacuolation occurred after repeated sonication. This noninvasive technology offers the possibility of controlling the extent of drug delivery by means of repeated treatment and adjusting the duration and interval between sonications.

Quantitative evaluation of the use of microbubbles with transcranial focused ultrasound on blood–brain-barrier disruption

It has been shown that focused ultrasound (FUS) can disrupt the blood–brain barrier (BBB) noninvasively and reversibly at target locations when applied in the presence of ultrasound contrast agent (UCA). In this study, the dose-dependent effects of UCA on BBB disruption were investigated in the brains of 16 male Wistar rats sonicated by 1.0-MHz transcranial FUS, with the UCA present at four doses. The BBB disruption was evaluated quantitatively based on the extravasation of Evans blue (EB). The amount of EB extravasation in the brain increased with the quantity of UCA injected into the femoral vein prior to sonication. Moreover, the use of a suitable dose of UCA resulted in the BBB disruption being concentrated in the focal region instead of the entire brain. Our results indicate that injecting an appropriate quantity of UCA effectively increases and localizes the BBB disruption induced by transcranial FUS sonications.

Real-time control of focused ultrasound heating based on rapid MR thermometry.

Real-time control of the heating procedure is essential for hyperthermia applications of focused ultrasound (FUS). The objective of this study is to demonstrate the feasibility of MRI-controlled FUS. An automatic control system was developed using a dedicated interface between the MR system control computer and the FUS wave generator. Two algorithms were used to regulate FUS power to maintain the focal point temperature at a desired level. Automatic control of FUS power level was demonstrated ex vivo at three target temperature levels (increase of 5 degrees C, 10 degrees C, and 30 degrees C above room temperature) during 30-minute hyperthermic periods. Preliminary in vivo results on rat leg muscle confirm that necrosis estimate, calculated on-line during FUS sonication, allows prediction of tissue damage. CONCLUSIONS. The feasibility of fully automatic FUS control based on MRI thermometry has been demonstrated.