FUS-induced Blood-brain Barrier Opening Research Articles

Regulation of P-glycoprotein and Breast Cancer Resistance Protein Expression Induced by Focused Ultrasound-Mediated Blood-Brain Barrier Disruption: A Pilot Study.

The blood-brain barrier (BBB) controls brain homeostasis; it is formed by vascular endothelial cells that are physically connected by tight junctions (TJs). The BBB expresses efflux transporters such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), which limit the passage of substrate molecules from blood circulation to the brain. Focused ultrasound (FUS) with microbubbles can create a local and reversible detachment of the TJs. However, very little is known about the effect of FUS on the expression of efflux transporters. We investigated the in vivo effects of moderate acoustic pressures on both P-gp and BCRP expression for up to two weeks after sonication. Magnetic resonance-guided FUS was applied in the striatum of 12 rats. P-gp and BCRP expression were determined by immunohistochemistry at 1, 3, 7, and 14 days postFUS. Our results indicate that FUS-induced BBB opening is capable of (i) decreasing P-gp expression up to 3 days after sonication in both the treated and in the contralateral brain regions and is capable of (ii) overexpressing BCRP up to 7 days after FUS in the sonicated regions only. Our findings may help improve FUS-aided drug delivery strategies by considering both the mechanical effect on the TJs and the regulation of P-gp and BCRP.

NIR-II fluorescence visualization of ultrasound-induced blood–brain barrier opening for enhanced photothermal therapy against glioblastoma using indocyanine green microbubbles

Focused ultrasound (FUS)-induced blood–brain barrier (BBB) opening is crucial for enhancing glioblastoma (GBM) therapies. However, an in vivo imaging approach with a high spatial–temporal resolution to monitor the BBB opening process in situ and synchronously is still lacking. Herein, we report the use of indocyanine green (ICG)-dopped microbubbles (MBs-ICG) for visualizing the FUS-induced BBB opening and enhancing the photothermal therapy (PTT) against GBM. The MBs-ICG show bright fluorescence in the second near-infrared window (NIR-II), ultrasound contrast, and ultrasound-induced size transformation properties. By virtue of complementary contrast properties, MBs-ICG can be successfully applied for cerebral vascular imaging with NIR-II fluorescence resolution of ∼168.9 μm and ultrasound penetration depth of ∼7 mm. We further demonstrate that MBs-ICG can be combined with FUS for in situ and synchronous visualization of the BBB opening with a NIR-II fluorescence signal-to-background ratio of 6.2 ± 1.2. Finally, our data show that the MBs-ICG transform into lipid-ICG nanoparticles under FUS irradiation, which then rapidly penetrate the tumor tissues within 10 min and enhance PTT in orthotopic GBM-bearing mice. The multifunctional MBs-ICG approach provides a novel paradigm for monitoring BBB opening and enhancing GBM therapy.

Blood–brain barrier opening in a large animal model using closed-loop microbubble cavitation-based feedback control of focused ultrasound sonication

Focused ultrasound (FUS) in combination with microbubbles has been established as a promising technique for noninvasive and localized Blood–brain barrier (BBB) opening. Real-time passive cavitation detection (PCD)-based feedback control of the FUS sonication is critical to ensure effective BBB opening without causing hemorrhage. This study evaluated the performance of a closed-loop feedback controller in a porcine model. Calibration of the baseline cavitation level was performed for each targeted brain location by a FUS sonication in the presence of intravenously injected microbubbles at a low acoustic pressure without inducing BBB opening. The target cavitation level (TCL) was defined for each target based on the baseline cavitation level. FUS treatment was then performed under real-time PCD-based feedback controller to maintain the cavitation level at the TCL. After FUS treatment, contrast-enhanced MRI and ex vivo histological staining were performed to evaluate the BBB permeability and safety. Safe and effective BBB opening was achieved with the BBB opening volume increased from 3.8 ± 0.7 to 53.6 ± 23.3 mm3 as the TCL was increased from 0.25 to 1 dB. This study validated that effective and safe FUS-induced BBB opening in a large animal model can be achieved with closed-loop feedback control of the FUS sonication.

Recent Trend of Ultrasound-Mediated Nanoparticle Delivery for Brain Imaging and Treatment.

In view of the fact that the blood-brain barrier (BBB) prevents the transport of imaging probes and therapeutic agents to the brain and thus hinders the diagnosis and treatment of brain-related disorders, methods of circumventing this problem (e.g., ultrasound-mediated nanoparticle delivery) have drawn much attention. Among the related techniques, focused ultrasound (FUS) is a favorite means of enhancing drug delivery via transient BBB opening. Photoacoustic brain imaging relies on the conversion of light into heat and the detection of ultrasound signals from contrast agents, offering the benefits of high resolution and large penetration depth. The extensive versatility and adjustable physicochemical properties of nanoparticles make them promising therapeutic agents and imaging probes, allowing for successful brain imaging and treatment through the combined action of ultrasound and nanoparticulate agents. FUS-induced BBB opening enables nanoparticle-based drug delivery systems to efficiently access the brain. Moreover, photoacoustic brain imaging using nanoparticle-based contrast agents effectively visualizes brain morphologies or diseases. Herein, we review the progress in the simultaneous use of nanoparticles and ultrasound in brain research, revealing the potential of ultrasound-mediated nanoparticle delivery for the effective diagnosis and treatment of brain disorders.

Cavitation-modulated inflammatory response following focused ultrasound blood-brain barrier opening

Focused ultrasound (FUS) in combination with systemically injected microbubbles can be used to non-invasively open the blood-brain barrier (BBB) in targeted regions for a variety of therapeutic applications. Over the past two decades, preclinical research into the safety and efficacy of FUS-induced BBB opening has proven this technique to be transient and efficacious, propelling FUS-induced BBB opening into several clinical trials in recent years. However, as clinical trials further progress, the neuroinflammatory response to FUS-induced BBB opening needs to be better understood. In this study, we provide further insight into the relationship of microbubble cavitation and the resulting innate immune response to FUS-induced BBB opening. By keeping ultrasound parameters fixed (i.e. frequency, pressure, pulse length, etc.), three groups of mice were sonicated using a real-time cavitation controller until a target cavitation dose was reached (1 x 107 V2•s, 5 x 107 V2•s, 1 x 108 V2•s). The change in relative gene expression of the mouse inflammatory cytokines and receptors were evaluated at three different time-points (6 h, 24 h, and 72 h) after FUS. At both 6 and 24 h time-points, significant changes in relative gene expression of inflammatory cytokines and receptors were observed across all cavitation groups. However, the degree of changes in relative expression levels and the number of genes with significant changes in expression varied across the cavitation groups. Groups with a higher cavitation dose exhibited both greater changes in relative expression levels and greater number of significant changes. By 72 h post-opening, the gene expression levels returned to baseline in all cavitation dose groups, signifying a transient inflammatory response to FUS-induced BBB opening at the targeted cavitation dose levels. Furthermore, the real-time cavitation controller was able to produce consistent and significantly different BBB permeability enhancement volumes across the three different cavitation dose groups. These results indicate that cavitation monitoring and controlling during FUS-induced BBB opening can be used to potentially modulate or limit the degree of neuroinflammation, further emphasizing the importance of implementing cavitation controllers as FUS-induced BBB opening is translated into the clinic.

Enhanced therapeutic effect of anti-EGFR cetuximab antibody on glioblastoma by focused ultrasound in preclinical model (+ Running poster)

Glioblastoma multiforme (GBM) is a very aggressive brain tumor, highly lethal. Overexpression of epidermal growth factor receptor (EGFR) and its mutant EGFR variant III are frequent in GBM [1] . They have shown to play a key role in the development and the growth of tumor cells. Several therapeutic strategies that target EGFR or its mutant have been developed, such as anti-EGFR monoclonal antibodies (mAb). One of them, the cetuximab (CTX) is interesting since it can block EGFR and EGFRvIII [2] . However, the blood-brain barrier (BBB) is one of the main limiting factor that restrains tumor penetration and decreases the efficacy of this immunotherapy. To overcome this issue, we have shown that the combination of injected microbubbles (MB) with low intensity focused ultrasound (FUS) transiently opened the BBB and enhanced CTX deliver in healthy brain, using immuno-PET imaging [3] , [4] . Here, we evaluated in mice the therapeutic benefits of repeated therapy (5 ×) combining the administration of CTX (40 mg/kg, iv.) with or without FUS-induced BBB opening. In vivo studies were performed on nude mice orthotopically grafted with human glioma cells (U251, 150,000 cells/injection) that overexpress EGFR. Survival rate has been investigated to evaluate the efficacy of the therapy on 4 different groups: sham with MB alone ( n = 5), FUS and MB ( n = 5), MB and CTX only ( n = 10), and MB + CTX + FUS ( n = 11). Furthermore, the delivery of radiolabeled CTX (89Zr, t1/2 = 3.3 days) into tumors has been quantified using PET imaging under two conditions: MB alone ( n = 6) or MB and FUS ( n = 5). As expected, CTX therapy alone without BBB opening in GBM model slightly improves median survival compared to the sham group (42 days vs. 29 days, not significant P = 0.1131). BBB opening helps to increase the significance of CTX therapeutic effect without improving drastically the immunotherapy efficacy. Maximal CTX therapeutic efficacy might be already achieved in the brain without FUS or anti-EGFR resistance might be developed overtime. Additional imaging and ex-vivo characterizations are ongoing to investigate this hypothesis.

Contrast-Free Detection of Focused Ultrasound-Induced Blood-Brain Barrier Opening Using Diffusion Tensor Imaging.

Focused ultrasound (FUS) has emerged as a non-invasive technique to locally and reversibly disrupt the blood-brain barrier (BBB). Here, we investigate the use of diffusion tensor imaging (DTI) as a means of detecting FUS-induced BBB opening at the absence of an MRI contrast agent. A non-human primate (NHP) was repeatedly treated with FUS and preformed circulating microbubbles to transiently disrupt the BBB (n = 4). T1- and diffusion-weighted MRI scans were acquired after the ultrasound treatment, with and without gadolinium-based contrast agent, respectively. Both scans were registered with a high-resolution T1-weighted scan of the NHP to investigate signal correlations. DTI detected an increase in fractional anisotropy from 0.21 ± 0.02 to 0.38 ± 0.03 (82.6 ± 5.2% change) within the targeted area one hour after BBB opening. Enhanced DTI contrast overlapped by 77.22 ± 9.2% with hyper-intense areas of gadolinium-enhanced T1-weighted scans, indicating diffusion anisotropy enhancement only within the BBB opening volume. Diffusion was highly anisotropic and unidirectional within the treated brain region, as indicated by the direction of the principal diffusion eigenvectors. Polar and azimuthal angle ranges decreased by 35.6% and 82.4%, respectively, following BBB opening. Evaluation of the detection methodology on a second NHP (n = 1) confirmed the across-animal feasibility of the technique. In conclusion, DTI may be used as a contrast-free MR imaging modality in lieu of contrast-enhanced T1 mapping for detecting BBB opening during focused-ultrasound treatment or evaluating BBB integrity in brain-related pathologies.

Investigating the optimum size of nanoparticles for their delivery into the brain assisted by focused ultrasound-induced blood\u2013brain barrier opening

The blood–brain barrier (BBB) has hampered the efficiency of nanoparticle delivery into the brain via conventional strategies. The widening of BBB tight junctions via focused ultrasound (FUS) offers a promising approach for enhancing the delivery of nanoparticles into the brain. However, there is currently an insufficient understanding of how nanoparticles pass through the opened BBB gaps. Here we investigated the size-dependence of nanoparticle delivery into the brain assisted by FUS-induced BBB opening, using gold nanoparticles (AuNPs) of 3, 15, and 120 nm diameter. For 3- and 15-nm AuNPs, FUS exposure significantly increased permeation across an in vitro BBB model by up to 9.5 times, and the permeability was higher with smaller diameter. However, in vivo transcranial FUS exposure in mice demonstrated that smaller particles were not necessarily better for delivery into the brain. Medium-sized (15 nm) AuNPs showed the highest delivery efficiency (0.22% ID), compared with 3- and 120-nm particles. A computational model suggested that this optimum size was determined by the competition between their permeation through opened BBB gaps and their excretion from blood. Our results would greatly contribute to designing nanoparticles for their delivery into the brain for the treatment of central nervous system diseases.

β-Amyloid Plaque Reduction in the Hippocampus After Focused Ultrasound-Induced Blood-Brain Barrier Opening in Alzheimer's Disease.

The blood–brain barrier (BBB) limits therapeutic delivery in Alzheimer’s disease (AD) and other neurological disorders. Animal models have demonstrated safe BBB opening and reduction in β-amyloid plaque with focused ultrasound (FUS). We recently demonstrated the feasibility, safety, and reversibility of FUS-induced BBB opening in the hippocampus and entorhinal cortex in six participants with early AD. We now report the effect of BBB opening with FUS treatment on β-amyloid plaque. Six participants underwent 18F-Florbetaben PET scan at baseline and 1 week after the completion of the third FUS treatment (60 days interval). PET analysis comparing the hippocampus and entorhinal cortex in the treated and untreated hemispheres revealed a decrease in the ratio of 18F-Florbetaben ligand binding. The standard uptake value ratios (SUVr) reduction ranged from 2.7% to 10% with an average of 5.05% (±2.76) suggesting a decrease in β-amyloid plaque.

Characterize brain tumor genetic signatures with focused ultrasound-enabled liquid biopsy

Although blood-based liquid biopsy is a promising noninvasive diagnostic technique, the blood-brain barrier (BBB) hinders the efficient transport of brain tumor biomarkers into the bloodstream. In our previous studies, we demonstrated the feasibility for focused ultrasound-enabled liquid biopsy (FUS-LBx) to increase BBB permeability and enhance the transport of glioblastoma (GBM)-specific biomarkers into the bloodstream of mice using mRNA as a model biomarker. The objective of this study was to demonstrate the clinical translatability of FUS-LBx by evaluating the enhanced transport of the GBM-specific gene mutation, epidermal growth factor receptor variant III (EGFRvIII). Rats were randomly assigned to the treated (n = 10) or control groups (n = 6) 10 days after F98-EGFRvIII tumor cell implantation. MRI scans guided the combined FUS and microbubble sonication to the tumor center and verified successful BBB disruption. Blood was collected after FUS sonication or sham treatment. Droplet digital polymerase chain reaction was used to analyze the EGFRvIII complementary DNA. Rat brains were collected for histological analysis of potential FUS-induced tissue damage. MRI scans confirmed successful FUS-induced BBB opening. The EGFRvIII mutation that was undetectable by conventional LBx (no FUS), was detected by FUS-LBx. Histological analysis showed no significant tissue damage caused by FUS. This study demonstrated that FUS-LBx has the clinical translational potential for the noninvasive characterization of the GBM genetic profiles.

Magnetic Resonance Methods for Focused Ultrasound-Induced Blood-Brain Barrier Opening

Since its discovery in 2001, the interest in the low-intensity focused ultrasound (FUS)-mediated blood-brain barrier (BBB) disruption to deliver genes and drugs to brain tissue has increased steadily. Increasingly sophisticated sonication protocols and dedicated hardware are being developed to efficiently and safely permeabilize the BBB, and novel magnetic resonance (MR)-based technologies have been designed to guide FUS-induced BBB opening protocols. MR imaging (MRI) allows not only to more precisely target brain regions and evaluate the outcome of sonication in terms of enhanced BBB permeability but also to control the effects of ultrasound on brain structure and function. This review summarizes the state of the art in current MRI hardware and methods used in BBB opening protocols both in pre-clinical and clinical settings.

Focused ultrasound enhanced intranasal delivery of brain derived neurotrophic factor produces neurorestorative effects in a Parkinson\u2019s disease mouse model

Focused ultrasound-enhanced intranasal (IN + FUS) delivery is a noninvasive approach that utilizes the olfactory pathway to administer pharmacological agents directly to the brain, allowing for a more homogenous distribution in targeted locations compared to IN delivery alone. However, whether such a strategy has therapeutic values, especially in neurodegenerative disorders such as Parkinson’s disease (PD), remains to be established. Herein, we evaluated whether the expression of tyrosine hydroxylase (TH), the rate limiting enzyme in dopamine catalysis, could be enhanced by IN + FUS delivery of brain-derived neurotrophic factor (BDNF) in a toxin-based PD mouse model. Mice were put on the subacute dosing regimen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), producing bilateral degeneration of the nigrostriatal pathway consistent with early-stage PD. MPTP mice then received BDNF intranasally followed by multiple unilateral FUS-induced blood-brain barrier (BBB) openings in the left basal ganglia for three consecutive weeks. Subsequently, mice were survived for two months and were evaluated morphologically and behaviorally to determine the integrity of their nigrostriatal dopaminergic pathways. Mice receiving IN + FUS had significantly increased TH immunoreactivity in the treated hemisphere compared to the untreated hemisphere while mice receiving only FUS-induced BBB opening or no treatment at all did not show any differences. Additionally, behavioral changes were only observed in the IN + FUS treated mice, indicating improved motor control function in the treated hemisphere. These findings demonstrate the robustness of the method and potential of IN + FUS for the delivery of bioactive factors for treatment of neurodegenerative disorder.

Empirical and Theoretical Characterization of the Diffusion Process of Different Gadolinium-Based Nanoparticles within the Brain Tissue after Ultrasound-Induced Permeabilization of the Blood-Brain Barrier.

Low-intensity focused ultrasound (FUS), combined with microbubbles, is able to locally, and noninvasively, open the blood-brain barrier (BBB), allowing nanoparticles to enter the brain. We present here a study on the diffusion process of gadolinium-based MRI contrast agents within the brain extracellular space after ultrasound-induced BBB permeabilization. Three compounds were tested (MultiHance, Gadovist, and Dotarem). We characterized their diffusion through in vivo experimental tests supported by theoretical models. Specifically, by estimation of the free diffusion coefficients from in vitro studies and of apparent diffusion coefficients from in vivo experiments, we have assessed tortuosity in the right striatum of 9 Sprague Dawley rats through a model correctly describing both vascular permeability as a function of time and diffusion processes occurring in the brain tissue. This model takes into account acoustic pressure, particle size, blood pharmacokinetics, and diffusion rates. Our model is able to fully predict the result of a FUS-induced BBB opening experiment at long space and time scales. Recovered values of tortuosity are in agreement with the literature and demonstrate that our improved model allows us to assess that the chosen permeabilization protocol preserves the integrity of the brain tissue.

Noninvasive and Local Delivery of Adenoviral-Mediated Herpes Simplex Virus Thymidine Kinase to Treat Glioma Through Focused Ultrasound-Induced Blood-Brain Barrier Opening in Rats.

Adenoviral-mediated gene therapy has been shown great prospects for tumor treatment. However, it is still a great challenge for its application in the glioma. A main cause is the blood-brain barrier (BBB) limits the delivery of adenoviral vectors, greatly compromising their efficacy. Here, we used focused ultrasound (FUS) induced microbubble cavitation to locally and reversibly open BBB for enhancing gene delivery. In this study, Ad-CMV-TK-IRES-EGFP (Ad-HSV-TK-EGFP) carrying the herpes simplex virus thymidine kinase (HSV-TK) and EGFP transgenes was chose as gendicine and Ad-CMV-IRES-EGFP (Ad-EGFP) as the control. The in vitro experiments showed that Ad-HSV-TK-EGFP had a high infection efficiency for C6 glioma cells, producing good tumor cell killing effects when these cells were exposed to more than 10 μg/ml ganciclovir (GCV). Taking advantage of FUS-induced BBB opening, Ad-HSV-TK-EGFP could be effectively delivered into the brain tumors, getting the overexpression of HSV-TK gene in the tumor cells. After exposure to GCV, the significantly stronger anti-tumor efficacy and longer survival time were observed in tumor-bearing mice treated with Ad-HSV-TK-EGFP + FUS than those treated with Ad-EGFP + FUS or only Ad-HSV-TK-EGFP. Histological examination indicated that the reduced expression level of Ki67 proteins and the increased apoptotic tumor cells in tumor xenografts, causing the inhibition of tumor growth. In conclusion, our study provided a new strategy to efficiently and locally deliver recombinant adenoviral vector-mediated HSV-TK gene into the brain to treat glioma.

Focused Ultrasound Induced-Blood-Brain Barrier Opening in Post-Radiosurgery Mouse Brain for Locally-Enhanced Systemic Therapy

Focused ultrasound (FUS) is a novel technique that is capable of non-invasively and transiently open the blood-brain barrier (BBB). It has been show that FUS can facilitate the delivery of systemically administered therapeutic agents. Our goal here is to investigate FUF induced BBB opening in a post stereotactic radiosurgery (SRS) mouse model for novel locally-enhanced systemic therapy. We hypothesized that microvascular effects of radiation could modulate the BBB-opening induced by FUS. In this study, normal brains of C57B5 mice were treated with a fractionated SRS dose, typically given to resected tumor cavities. A single beam radiation (6Gy x 5 daily fractions) was delivered through a 10×10 mm2 collimator to half of the mouse brain using the Small Animal Radiation Research Platform (SARRP). The dose delivered to the mice was verified via two mouse-like anthropomorphic phantoms in the axial and sagittal orientations. Upon the completion of SARRP treatments, mice were divided into two groups for FUS-induced BBB opening on day 7 (acute) and day 35 (chronic), respectively. A 1.5 MHz single element FUS transducer (-6dB focal zone was 1×1×7.5 mm3) was used for all sonications. The caudate-putamen (CPu) was the FUS target and four 30s sonications were delivered on each side of the brain. The BBB opening was confirmed with contrast-enhanced T1-weighted MRI scans, while dynamic MRI scans were also performed to evaluate the blood vessel permeability. The animals were sacrificed 2 hours post sonications and lectin was injected to label the vasculature. The isodose lines from the mouse-like phantom experiment agreed well with the projected values. BBB was successfully opened after FUS sonications on both sides of the brain (with or without radiation) as evidenced by contrast-enhanced MRI. In the acute group, higher gadolinium concentration (p = 0.072) was observed on the RT positive side. MR dynamic imaging revealed a similar trend in which RT positive side had a higher (p = 0.158) vascular permeability. Although the mean vessel area in the sonicated area remained similar between the two sides, significantly less lectin labeling (blood vessel density) was observed on the RT positive hemisphere (p = 0.003) in the acute group. These observations can be attributed to increased vasculature vulnerability immediately post SRS (within 2 days) resulting in more profound BBB opening. Interestingly, this difference diminished one month later in the chronic group, where FUS elicited comparable BBB openings and minimal vascular density changes in the CPu on both sides. Localized BBB opening can be successfully induced by FUS in previously stereotactically irradiated normal brains. BBB openings were evident in both acute and chronic settings with potentially more profound outcomes if FUS is performed within 2 days of RT treatment.

Focused ultrasound induced opening of the blood-brain barrier disrupts inter-hemispheric resting state functional connectivity in the rat brain

Focused ultrasound (FUS) is a technology capable of delivering therapeutic levels of energy through the intact skull to a tightly localized brain region. Combining the FUS pressure wave with intravenously injected microbubbles creates forces on blood vessel walls that open the blood-brain barrier (BBB). This noninvasive and localized opening of the BBB allows for targeted delivery of pharmacological agents into the brain for use in therapeutic development. It is possible to use FUS power levels such that the BBB is opened without damaging local tissues. However, open questions remain related to the effects that FUS-induced BBB opening has on brain function including local physiology and vascular hemodynamics. We evaluated the effects that FUS-induced BBB opening has on resting state functional magnetic resonance imaging (rs-fMRI) metrics. Data from rs-fMRI was acquired in rats that underwent sham FUS BBB vs. FUS BBB opening targeted to the right primary somatosensory cortex hindlimb region (S1HL). FUS BBB opening reduced the functional connectivity between the right S1HL and other sensorimotor regions, including statistically significant reduction of connectivity to the homologous region in the left hemisphere (left S1HL). The effect was observed in all three metrics analyzed: functional connectivity between anatomically defined regions, whole brain voxel-wise correlation maps based on anatomical seeds, and spatial patterns from independent component analysis. Connectivity metrics for other regions where the BBB was not perturbed were not affected. While it is not clear whether the effect is vascular or neuronal in origin, these results suggest that even safe levels of FUS BBB opening have an effect on the physiological processes that drive the signals measured by BOLD fMRI. As such these effects must be accounted for when carrying out studies using fMRI to evaluate the effects of pharmacological agents delivered via FUS-induced BBB opening.

Image-Guided Focused-Ultrasound CNS Molecular Delivery: An Implementation via Dynamic Contrast-Enhanced Magnetic-Resonance Imaging.

Focused ultrasound (FUS) exposure with microbubbles can transiently open the blood-brain barrier (BBB) to deliver therapeutic molecules into CNS tissues. However, delivered molecular distribution/concentration at the target need to be controlled. Dynamic Contrast-Enhanced Magnetic-Resonance Imaging (DCE-MRI) is a well-established protocol for monitoring the pharmacokinetic/pharmacodynamic behavior of FUS-BBB opening. This study investigates the feasibility of using DCE-MRI to estimate molecular CNS penetration under various exposure conditions and molecule sizes. In the 1st stage, a relationship among the imaging index Ktrans, exposure level and molecular size was calibrated and established. In the 2nd stage, various exposure levels and distinct molecules were applied to evaluate the estimated molecular concentration discrepancy with the quantified ones. High correlation (r2 = 0.9684) between Ktrans and transcranial mechanical index (MI) implies Ktrans can serve as an in vivo imaging index to mirror FUS-BBB opening scale. When testing various molecules with the size ranging 1–149 kDa, an overall correlation of r2 = 0.9915 between quantified and predicted concentrations was reached, suggesting the established model can provide reasonably accurate estimation. Our work demonstrates the feasibility of estimating molecular penetration through FUS-BBB opening via DCE-MRI and may facilitate development of FUS-induced BBB opening in brain drug delivery.

Three-dimensional transcranial microbubble imaging for guiding volumetric ultrasound-mediated blood-brain barrier opening.

Focused ultrasound (FUS)-mediated blood-brain barrier (BBB) opening recently entered clinical testing for targeted drug delivery to the brain. Sources of variability exist in the current procedures, motivating the development of real-time monitoring and control techniques to improve treatment safety and efficacy. Here we used three-dimensional (3D) transcranial microbubble imaging to calibrate FUS exposure levels for volumetric BBB opening.Methods: Using a sparse hemispherical transmit/receive ultrasound phased array, pulsed ultrasound was focused transcranially into the thalamus of rabbits during microbubble infusion and multi-channel 3D beamforming was performed online with receiver signals captured at the subharmonic frequency. Pressures were increased pulse-by-pulse until subharmonic activity was detected on acoustic imaging (psub), and tissue volumes surrounding the calibration point were exposed at 50-100%psub via rapid electronic beam steering.Results: Spatially-coherent subharmonic microbubble activity was successfully reconstructed transcranially in vivo during calibration sonications. Multi-point exposures induced volumetric regions of elevated BBB permeability assessed via contrast-enhanced magnetic resonance imaging (MRI). At exposure levels ≥75%psub, MRI and histological examination occasionally revealed tissue damage, whereas sonications at 50%psub were performed safely. Substantial intra-grid variability of FUS-induced bioeffects was observed via MRI, prompting future development of multi-point calibration schemes for improved treatment consistency. Receiver array sparsity and sensor configuration had substantial impacts on subharmonic detection sensitivity, and are factors that should be considered when designing next-generation clinical FUS brain therapy systems.Conclusion: Our findings suggest that 3D subharmonic imaging can be used to calibrate exposure levels for safe FUS-induced volumetric BBB opening, and should be explored further as a method for cavitation-mediated treatment guidance.

Characterization of Different Microbubbles in Assisting Focused Ultrasound-Induced Blood-Brain Barrier Opening

Microbubbles (MBs) serve as a critical catalyst to amplify local cavitation in CNS capillary lumen to facilitate focused ultrasound (FUS) to transiently open the blood-brain barrier (BBB). However, limited understanding is available regarding the effect of different microbubbles to induce BBB opening. The aim of this study is to characterize different MBs on their effect in FUS-induced BBB opening. Three MBs, SonoVue, Definity, and USphere, were tested, with 0.4-MHz FUS exposure at 0.62–1.38 of mechanical index (MI) on rats. Evans blue, dynamic contrast-enhanced (DCE) MRI and small-animal ultrasound imaging were used as surrogates to allow molecule-penetrated quantification, BBB-opened observation, and MBs circulation/persistence. Cavitation activity was measured via the passive cavitation detection (PCD) setup to correlate with the exposure level and the histological effect. Under given and identical MB concentrations, the three MBs induced similar and equivalent BBB-opening effects and persistence. In addition, a treatment paradigm by adapting exposure time is proposed to compensate MB decay to retain the persistence of BBB-opening efficiency in multiple FUS exposures. The results potentially improve understanding of the equivalence among MBs in focused ultrasound CNS drug delivery, and provide an effective strategy for securing persistence in this treatment modality.

Targeting Effects on the Volume of the Focused Ultrasound-Induced Blood-Brain Barrier Opening in Nonhuman Primates In Vivo.

Drug delivery to subcortical regions is susceptible to the blood-brain barrier (BBB) impeding the molecular exchange between the blood stream and the brain parenchyma. Focused ultrasound (FUS) coupled with the administration of microbubbles has been proved to open the BBB locally, transiently, and noninvasively both in rodents and in nonhuman-primates (NHPs). The development of this disruption technique independent of MRI monitoring is of primordial importance yet restrained to the targeting optimization. This paper establishes the linear relationship of the incidence angle with the volume of BBB opening ( VBBB ) and the peak negative pressure when sonicating the caudate nucleus and the putamen region of five NHPs. In addition, the effect of central nervous system structures on the opening morphology is evaluated by identification of the gray-to-white-matter ratio at the opening site. Finally, the targeting accuracy is assessed through the estimation of the geometric and angle shift of the opening from the targeted region. Interestingly, results prove a monotonic increase of the opening volume with close to normal incidence angles. Moreover, 80.35% of the opening lies on gray-matter regions compared with only 19.41% attributed to the white matter. The opening was found to be shifted axially, toward the transducer, and laterally with an average angle shift of 4.5°. Finally, we were capable of showing reproducibility of targeting accuracy with the same stereotactic and ultrasonic parameters. This paper documents the a priori prediction of the opening volume through manipulation of the angle and pressure as well as establishing the predictability, accuracy, and safety of FUS-induced BBB opening in NHPs.