Ultrasound Setup Research Articles

Real-Time Multiphoton Intravital Microscopy of Drug Extravasation in Tumours during Acoustic Cluster Therapy.

Optimising drug delivery to tumours remains an obstacle to effective cancer treatment. A prerequisite for successful chemotherapy is that the drugs reach all tumour cells. The vascular network of tumours, extravasation across the capillary wall and penetration throughout the extracellular matrix limit the delivery of drugs. Ultrasound combined with microbubbles has been shown to improve the therapeutic response in preclinical and clinical studies. Most studies apply microbubbles designed as ultrasound contrast agents. Acoustic Cluster Therapy (ACT®) is a novel approach based on ultrasound-activated microbubbles, which have a diameter 5-10 times larger than regular contrast agent microbubbles. An advantage of using such large microbubbles is that they are in contact with a larger part of the capillary wall, and the oscillating microbubbles exert more effective biomechanical effects on the vessel wall. In accordance with this, ACT® has shown promising therapeutic results in combination with various drugs and drug-loaded nanoparticles. Knowledge of the mechanism and behaviour of drugs and microbubbles is needed to optimise ACT®. Real-time intravital microscopy (IVM) is a useful tool for such studies. This paper presents the experimental setup design for visualising ACT® microbubbles within the vasculature of tumours implanted in dorsal window (DW) chambers. It presents ultrasound setups, the integration and alignment of the ultrasound field with the optical system in live animal experiments, and the methodologies for visualisation and analysing the recordings. Dextran was used as a fluorescent marker to visualise the blood vessels and to trace drug extravasation and penetration into the extracellular matrix. The results reveal that the experimental setup successfully recorded the kinetics of extravasation and penetration distances into the extracellular matrix, offering a deeper understanding of ACT's mechanisms and potential in localised drug delivery.

European Society of Pediatric Radiology survey of perioperative imaging in pediatric liver transplantation: (2) intraoperative imaging

BackgroundLiver transplantation is the state-of-the-art curative treatment for end-stage liver disease. Imaging is a key element in the detection of intraoperative and postoperative complications. So far, only limited data regarding the best radiological approach to monitor children during liver transplantation is available.ObjectiveTo harmonize the imaging of pediatric liver transplantation, the European Society of Pediatric Radiology Abdominal Taskforce initiated a survey addressing the current status of imaging including the pre-, intra- and postoperative phase. This paper reports the responses related to intraoperative imaging.Materials and methodsAn online survey, initiated in 2021, asked European centers performing pediatric liver transplantation 48 questions about their imaging approach. In total, 26 centers were contacted, and 22 institutions from 11 countries returned the survey.ResultsIntraoperative ultrasound (US) is used by all sites to assess the quality of the vascular anastomosis in order to ensure optimal perfusion of the liver transplant. Vessel depiction is commonly achieved using color Doppler (95.3%). Additional US-based techniques are employed by fewer centers (power angio mode, 28.6%; B-flow, 19%; contrast-enhanced US, 14.3%). Most centers prefer a collaborative approach, with surgeons responsible for probe handling, while radiologists operate the US machine (47.6%). Less commonly, the intraoperative US is performed by the surgeon alone (28.6%) or by the radiologist alone (23.8%). Timing of US, imaging frequency, and documentation practices vary among centers.ConclusionIntraoperative US is consistently utilized across all sites during pediatric liver transplantation. However, considerable variations were observed in terms of the US setup, technique preferences, timing of controls, and documentation practices. These differences provide valuable insights for future optimization and harmonization studies.

Abstract 12595: Vascular and Cardiac Ultrasound as the Primary Imaging Tool to Safely Deliver Pacing Leads While Implanting Single Chamber Cardiac Implantable Electronic Devices. RADICAI USE Investigators

Introduction: Conventional Cardiac implantable electronic devices (CIEDs) implantation requires fluoroscopy. Risks involved with implantation include pneumothorax, lead dislodgement, and perforation of the right ventricular wall. In addition, there are long-term risks of malignancy associated with prolonged and repeated use of radiation over the decades of operators’ employment and mechanical injuries related to heavy personal protection equipment. To reduce these risks, we aimed to study the utilization and safety of ultrasound (US) for the entire procedure to implant single-chamber devices. Methods: The RADICAI USE study (Reduction or Elimination of Radiation Use in Single Chamber Cardiac Devices using ultrasound) is a prospective, single-arm and multi-operator case series enrolled patients awaiting a single-chamber CIED. A fluoroscopic cut-off time of 20 seconds was used to define the success (Group A) or failure (Group B) of using the US for the entire implant duration. Patients were followed up at 1 week, 1 month and 1-year post-implant. Results: The study enrolled 63 patients, with 50 pacemakers and 13 ICDs, a mean age of 79.5 ± 13.8 years (95% CI = 76.1 - 82.9), and a mean weight of 74.1 ± 14.6 (95% CI = 70.5 - 77.7). Overall, 53 (84.1%) CIEDs were successfully implanted with a radiation time of less than 20 seconds (Group A). Fluoroscopic over 20 seconds was required due to poor echocardiographic windows, challenging access, or anatomy. No iatrogenic new or worsening of tricuspid regurgitation was noted. The mean procedure time including US setup time was 65.2 ± 20.2 (95% CI = 60.2 -70.2) minutes. Fluoroscopic time was significantly reduced in Group A compared to Group B (5.8 ± 4.5s vs 109.5 ± 92.9s, p = 0.004). Follow-up showed no device-related complications, with only two patients requiring lead revisions due to poor sensitivity, one unrelated to US use and another probably related. Conclusions: US-guided implantation of single-chamber CIEDs is feasible and safe, reducing the need for fluoroscopic guided implantation and subsequent risks of higher radiation exposure. Further studies are required to evaluate the cost-effectiveness and to explore fluoroscopic-free single-chamber CIED implantations using the US.

Stable Cavitation-Mediated Delivery of miR-126 to Endothelial Cells.

In endothelial cells, microRNA-126 (miR-126) promotes angiogenesis, and modulating the intracellular levels of this gene could suggest a method to treat cardiovascular diseases such as ischemia. Novel ultrasound-stimulated microbubbles offer a means to deliver therapeutic payloads to target cells and sites of disease. The purpose of this study was to investigate the feasibility of gene delivery by stimulating miR-126-decorated microbubbles using gentle acoustic conditions (stable cavitation). A cationic DSTAP microbubble was formulated and characterized to carry 6 µg of a miR-126 payload per 109 microbubbles. Human umbilical vein endothelial cells (HUVECs) were treated at 20-40% duty cycle with miR-126-conjugated microbubbles in a custom ultrasound setup coupled with a passive cavitation detection system. Transfection efficiency was assessed by RT-qPCR, Western blotting, and endothelial tube formation assay, while HUVEC viability was monitored by MTT assay. With increasing duty cycle, the trend observed was an increase in intracellular miR-126 levels, up to a 2.3-fold increase, as well as a decrease in SPRED1 (by 33%) and PIK3R2 (by 46%) expression, two salient miR-126 targets. Under these ultrasound parameters, HUVECs maintained >95% viability after 96 h. The present work describes the delivery of a proangiogenic miR-126 using an ultrasound-responsive cationic microbubble with potential to stimulate therapeutic angiogenesis while minimizing endothelial damage.

Prediction of vascular injury by cavitation microbubbles in a focused ultrasound field

Many studies have shown that microbubble cavitation is one mechanism for vascular injury under ultrasonic excitation. Previous work has attributed vascular damage to vessel expansions and invaginations due to the expansion and contraction of microbubbles. However, the mechanisms of vascular damage are not fully understood. In this paper, we investigate, theoretically and experimentally, the vessel injury due to stress induced by ultrasound-induced cavitation (UIC). A bubble-fluid-vessel coupling model is constructed to investigate the interactions of the coupling system. The dynamics process of vessel damage due to UIC is theoretically simulated with a finite element method, and a focused ultrasound (FU) setup is carried out and used to assess the vessel damage. The results show that shear stress contributes to vessel injury by cell detachment while normal stress mainly causes distention injury. Similar changes in cell detachment in a vessel over time can be observed with the experimental setup. The severity of vascular injury is correlated to acoustic parameters, bubble-wall distance, and microbubble sizes, and the duration of insonation..

Development of a Personal Ultrasound Exposimeter for Occupational Health Monitoring.

Prolonged exposure to airborne ultrasound in a workplace can have a detrimental influence on a worker’s well-being. Given the ever-increasing use of ultrasonic industrial equipment, it is of vital importance—and may also be regulated by law—to monitor ultrasound exposure during a normal workday as part of workplace risk assessment. However, the devices currently utilized exhibit limitations with regard to both their operational frequency and their portability (wearability). In this paper, the first prototype of a high-frequency and ultrasound personal exposimeter is presented in the light of the latest national and international standards governing high-frequency and ultrasonic noise measurement in the field of occupational health monitoring. The prototype was tested in the laboratory environment in order to assess its sound level detection capabilities in both the audible and ultrasonic frequency ranges. Several common industrial scenarios—including an ultrasonic welding machine, an ultrasonic cleaning bath, and a compressed air gun—were simulated in a laboratory environment. For each simulated set-up, a corresponding high-frequency or ultrasonic signal was fed through a specially prepared generation chain. Each experimental scenario was initially surveyed with an ultrasound level meter previously tested up to 100 kHz. This was followed by a measurement with the prototype. For this study, the simulated sound signals varied between 10 kHz and 40 kHz on the frequency scale and between 60 dB and 90 dB in amplitude. The portability of the prototype, which may be required to be worn throughout an entire workday (e.g., 8 h), was also considered. All the experiments were performed on a customized ultrasound measurement set-up within a free-field environment located at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. Results obtained suggest a good agreement between the measurements performed with both devices in the louder areas of the sound fields produced. Because the overall measurement uncertainty is highly dependent on the specificity of the individual measurement set-up and measurement procedure, an uncertainty budget estimated for the prototype considers electro-acoustical contributions only.

Controlling the Dynamics of Cloud Cavitation Bubbles through Acoustic Feedback

Cloud cavitation causes nontrivial energy concentration and acoustic shielding in liquid and its control is a long-standing challenge due to complex dynamics of bubble clouds. We present a framework to study closed-loop control of cavitation through acoustic feedback. While previous approaches have used empirical thresholding, we employ model-based state estimation of coherent bubble dynamics based on theory and high-performance computing. Using a pulsed ultrasound setup, we demonstrate set-point control of the pulse-repetition frequency (PRF) to modulate acoustic cavitation near a solid target over $O(100)$ s. We identify a quasiequilibrium correlation between the PRF and the bubble dynamics and an optimal PRF to minimize acoustic shielding of the target. This framework can be readily scaled up by enhanced acoustic sensing and computational power.

A High-Throughput Image-Guided Stereotactic Neuronavigation and Focused Ultrasound System for Blood-Brain Barrier Opening in Rodents.

The blood-brain barrier (BBB) has been a major hurdle for the treatment of various brain diseases. Endothelial cells, connected by tight junctions, form a physiological barrier preventing large molecules (>500 Da) from entering the brain tissue. Microbubble-mediated focused ultrasound (FUS) can be used to induce a transient local BBB opening, allowing larger drugs to enter the brain parenchyma. In addition to large-scale clinical devices for clinical translation, preclinical research for therapy response assessment of drug candidates requires dedicated small animal ultrasound setups for targeted BBB opening. Preferably, these systems allow high-throughput workflows with both high-spatial precision as well as integrated cavitation monitoring, while still being cost effective in both initial investment and running costs. Here, we present a bioluminescence and X-ray guided stereotactic small animal FUS system that is based on commercially available components and fulfills the aforementioned requirements. A particular emphasis has been placed on a high degree of automation facilitating the challenges typically encountered in high-volume preclinical drug evaluation studies. Examples of these challenges are the need for standardization in order to ensure data reproducibility, reduce intra-group variability, reduce sample size and thus comply with ethical requirements and decrease unnecessary workload. The proposed BBB system has been validated in the scope of BBB opening facilitated drug delivery trials on patient-derived xenograft models of glioblastoma multiforme and diffuse midline glioma.

Reliability of standardized ultrasound measurements of quadriceps muscle thickness in neurological critically ill patients: a comparison to computed tomography measures.

Muscle atrophy is frequent in critically ill patients and is associated with increased mortality and long-lasting alteration in quality of life. Muscle ultrasound has not been clearly validated in intensive care unit patients. The aim of this study was to compare the level of agreement between ultrasound and computed tomography scan for the measurement of quadriceps muscle thickness. A prospective observational study. Forty-two consecutive patients admitted to a neurological intensive care unit. Quadriceps thickness was measured 15 cm above the upper edge of the patella. Iterative brain computed tomography scans were associated with a quadriceps-centred acquisition sequence. Concomitantly, an ultrasound of the quadriceps was performed. The position of the studied leg was standardized for ultrasound and computed tomography. A total of 73 measurements of ultrasound and computed tomography quadriceps thickness were compared. The correlation between both measures was 0.93 (95% confidence interval (95% CI) 0.84-1.02). Intra-rater reliability of ultrasound measurements and inter-rater reliability were excellent, with an ICC of 0.98 (95% CI 0.97-0.99) and 0.96 (95% CI 0.92-0.98), respectively. A specific ultrasound set-up for measurement of quadriceps thickness is reliable and reproducible in an intensive care unit population.

Tracking geometric and hemodynamic alterations of an arteriovenous fistula through patient-specific modelling

Background and objective: The use of patient-specific CFD modelling for arteriovenous fistulae (AVF) has shown great clinical potential for improving surveillance, yet the use of imaging modes such as MRI and CT for the 3D geometry acquisition presents high costs and exposure risks, preventing regular use. We have developed an ultrasound based procedure to bypass these limitations.Methods: A scanning procedure and processing pipeline was developed specifically for CFD modelling of AVFs, using a freehand ultrasound setup combining B-mode scanning with 3D probe motion tracking. The scanning procedure involves sweeping along the vasculature to create a high density stack of B-mode frames containing the lumen geometry. This stack is converted into a continuous volume and transient flow waveforms are recorded at the boundaries, synchronised with ECG and automatically digitised, forming realistic boundary conditions for the CFD models. This is demonstrated on a diseased patient-specific AVF.Results: The three scans obtained using this procedure varied in geometry and flow behaviour, with regions of disease located in the first two scans. The outcome of the second procedure seen in the third scan indicated successful restoration with no sites of disease and higher flow. The models gave insight into the lumenal changes in diameter for both the artery and vein segments, as well as characterising hemodynamic behaviours in both the diseased and restored states. Vascular segment resistances obtained from the CFD models indicate a significant reduction once disease was removed, resulting in much higher flows enabling the patient to resume dialysis.Conclusion: The methodology described in this study allowed for a multifaceted analysis and high level tracking in terms of both geometry and flow behaviours for a patient case, demonstrating significant clinical utility and practicality, as well as enabling further research into vascular disease progression in AVFs through longitudinal analysis.

In vitro potentiation of doxorubicin by unseeded controlled non-inertial ultrasound cavitation

Ultrasound-generated non-inertial cavitation has the ability to potentiate the therapeutic effects of cytotoxic drugs. We report a novel strategy to induce and regulate unseeded (without nucleation agents) non-inertial cavitation, where cavitation is initiated, monitored and regulated using a confocal ultrasound setup controlled by an instrumentation platform and a PC programmed feedback control loop. We demonstrate, using 4T1 murine mammary carcinoma as model cell line, that unseeded non-inertial cavitation potentiates the cytotoxicity of doxorubicin, one of the most potent drugs used in the treatment of solid tumors including breast cancer. Combined treatment with doxorubicin and unseeded non-inertial cavitation significantly reduced cell viability and proliferation at 72 h. A mechanistic study of the potential mechanisms of action of the combined treatment identified the presence of cavitation as required to enhance doxorubicin efficacy, but ruled out the influence of changes in doxorubicin uptake, temperature increase, hydroxyl radical production and nuclear membrane modifications on the treatment outcome. The developed strategy for the reproducible generation and maintenance of unseeded cavitation makes it an attractive method as potential preclinical and clinical treatment modality to locally potentiate doxorubicin.

Portable Tracked Ultrasound System to Monitor Spinal Curvature

ntroduction: Adolescent idiopathic scoliosis (AIS) is the most frequent spinal deformation. It is assessed by frequent x-ray imaging, exposing patients to frequent radiation, increasing the risk of cancer. Tracked ultrasound imaging produce a three-dimensional visual of the spine without risk. We proposed using an optically tracked handheld USB Interson ultrasound probe, which is much less expensive than the current standard ultrasounds.
 Methods: A practical setup was developed for scoliosis monitoring. Reference markers were on the patient’s shoulder and the wall to account for patient motion, and simulate the plane of the x-ray detector to allow future comparisons. The optical tracker tracked the markers and ultrasound probe. This was compared to the electromagnetically tracked non-portable Ultrasonix ultrasound. Scanning captured the thoracic and lumbar regions. A three-dimensional image was composited by stacking a series of two-dimensional ultrasound slices in their tracked physical positions. To compare the two-ultrasound setups and ensure the ease of identification, a novice attempted to manually identify transverse processes. These were compared to see if all transverse processes scanned could be marked from both ultrasound setups. Two clinical experts then confirmed the markings were anatomically correct.
 Results and Conclusions: In all scans 100% of the transverse processes scanned (n = 51) were identified in Interson and Ultrasonix images. Curvatures measured using the Ultrasonix method have been previously validated to curvature measurements from x-ray images. Thus the 100% correspondence of the Interson and Ultrasonix setups indicates this inexpensive method is a promising tool to reduce radiation exposure during scoliosis monitoring.

Active phantoms: a paradigm for ultrasound calibration using phantom feedback.

In ultrasound (US)-guided medical procedures, accurate tracking of interventional tools is crucial to patient safety and clinical outcome. This requires a calibration procedure to recover the relationship between the US image and the tracking coordinate system. In literature, calibration has been performed on passive phantoms, which depend on image quality and parameters, such as frequency, depth, and beam-thickness as well as in-plane assumptions. In this work, we introduce an active phantom for US calibration. This phantom actively detects and responds to the US beams transmitted from the imaging probe. This active echo (AE) approach allows identification of the US image midplane independent of image quality. Both target localization and segmentation can be done automatically, minimizing user dependency. The AE phantom is compared with a crosswire phantom in a robotic US setup. An out-of-plane estimation US calibration method is also demonstrated through simulation and experiments to compensate for remaining elevational uncertainty. The results indicate that the AE calibration phantom can have more consistent results across experiments with varying image configurations. Automatic segmentation is also shown to have similar performance to manual segmentation.

Automated Generation of Reliable Blood Velocity Parameter Maps from Contrast-Enhanced Ultrasound Data.

Objectives The purpose of this study was the automated generation and validation of parametric blood flow velocity maps, based on contrast-enhanced ultrasound (CEUS) scans. Materials and Methods Ethical approval for animal experiments was obtained. CEUS destruction-replenishment sequences were recorded in phantoms and three different tumor xenograft mouse models. Systematic pixel binning and intensity averaging was performed to generate parameter maps of blood flow velocities with different pixel resolution. The 95% confidence interval of the mean velocity, calculated on the basis of the whole tumor segmentation, served as ground truth for the different parameter maps. Results In flow phantoms the measured mean velocity values were only weakly influenced by the pixel resolution and correlated with real velocities (r2 ≥ 0.94, p < 0.01). In tumor xenografts, however, calculated mean velocities varied significantly (p < 0.0001), depending on the parameter maps' resolution. Pixel binning was required for all in vivo measurements to obtain reliable parameter maps and its degree depended on the tumor model. Conclusion Systematic pixel binning allows the automated identification of optimal pixel resolutions for parametric maps, supporting textural analysis of CEUS data. This approach is independent from the ultrasound setup and can be implemented in the software of other (clinical) ultrasound devices.

Primary Porcine Brain Endothelial Cells as In Vitro Model to Study Effects of Ultrasound and Microbubbles on Blood-Brain Barrier Function.

Focused ultrasound (FUS) in the presence of microbubbles transiently and reversibly opens the blood-brain barrier (BBB) in rodents and humans, thereby providing a time window for increased drug delivery into brain tissue. To get insight into the underlying mechanisms that govern ultrasound (US)-mediated opening of the BBB, in vitro models are a useful alternative. In this paper, we have utilized an in vitro BBB model that consists of primary porcine brain endothelial cells (PBECs). PBEC monolayers are grown on permeable membranes, which allow assessment of key features of BBB function as well as US treatment. This experimental model is characterized by low permeability for both small molecules and proteins, has a high transendothelial electrical resistance, and expresses tight junctions and efflux pumps. Here, we compare the effects of inertial and stable cavitation in the presence of SonoVue microbubbles on PBEC monolayers' electrical resistance and permeability properties. Our results point out the fragility of PBEC monolayers, which enhances results variability. In particular, we show that handling of the inserts, such as medium change and transfer to the US setup, modifies the cellular response, and immunostaining of the monolayers introduces damage and cell detachment within the US-exposed monolayers. Our results indicate that stable cavitation might have a more pronounced impact on cell permeability as compared with inertial cavitation in vitro. This paper might contribute to further development of experimental setups that are suitable to characterize the impact of FUS and microbubbles on BBB properties in vitro.

Prolonged stimulation with low-intensity ultrasound induces delayed increases in spontaneous hippocampal culture spiking activity.

Ultrasound is a promising neural stimulation modality, but an incomplete understanding of its range and mechanism of effect limits its therapeutic application. We investigated the modulation of spontaneous hippocampal spike activity by ultrasound at a lower acoustic intensity and longer time scale than has been previously attempted, hypothesizing that spiking would change conditionally upon the availability of glutamate receptors. Using a 60-channel multielectrode array (MEA), we measured spontaneous spiking across organotypic rat hippocampal slice cultures (N = 28) for 3 min each before, during, and after stimulation with low-intensity unfocused pulsed or sham ultrasound (spatial-peak pulse average intensity 780 μW/cm2 ) preperfused with artificial cerebrospinal fluid, 300 μM kynurenic acid (KA), or 0.5 μM tetrodotoxin (TTX) at 3 ml/min. Spike rates were normalized and compared across stimulation type and period, subregion, threshold level, and/or perfusion condition using repeated-measures ANOVA and generalized linear mixed models. Normalized 3-min spike counts for large but not midsized, small, or total spikes increased after but not during ultrasound relative to sham stimulation. This result was recapitulated in subregions CA1 and dentate gyrus and replicated in a separate experiment for all spike size groups in slices pretreated with aCSF but not KA or TTX. Increases in normalized 18-sec total, midsized, and large spike counts peaked predominantly 1.5 min following ultrasound stimulation. Our low-intensity ultrasound setup exerted delayed glutamate receptor-dependent, amplitude- and possibly region-specific influences on spontaneous spike rates across the hippocampus, expanding the range of known parameters at which ultrasound may be used for neural activity modulation. © 2016 Wiley Periodicals, Inc.

Abstract 2073: Focused ultrasound-mediated transport of poly(alkyl) cyanoacrylate nanoparticles across the blood-brain barrier in a melanoma brain metastasis model

Abstract Drug delivery into the brain is impeded by the blood-brain barrier (BBB) - a dynamic interface that protects brain homeostasis, but also screens the brain from the vast majority of large and/or hydrophilic drug molecules. Focused ultrasound (FUS) has emerged as one of the promising methods to open the BBB safely and reversibly. We have previously reported FUS-mediated BBB opening using a novel platform consisting of microbubbles surrounded by poly(alkyl cyanoacrylate) nanoparticles that could prospectively be used for FUS- and nanoparticle-mediated drug delivery into the brain (1,2). Here, we have been investigating FUS-mediated BBB opening using a novel ultrasound system capable of generating FUS at two frequencies, 1.1 MHz and 7.8 MHz during the same experiment. This system allows a very precise selection of the exposure area. We used FUS exposure at 1 MHz to open the BBB by cavitation, while exposure at 7.8 MHz was employed to enable the action of acoustic radiation force. This force is caused by a transfer of momentum from acoustic waves to the tissues in which they propagate, and can facilitate nanoparticle transport in the extracellular matrix. FUS-mediated BBB opening was performed in NOD/SCID mice with melanoma brain metastases developed after intracardiac injection of human melanoma brain metastasis cells (3). The cells were fluorescently labeled, which enabled their detection in the brain. Poly(isohexyl) cyanoacrylate (PIHCA) nanoparticle-microbubbles similar to those reported in our earlier works (1,2) were injected immediately before the FUS exposure. Successful opening of the BBB was verified by MRI using a gadolinium-based contrast agent. An optimal window of exposure intensities that allow BBB disruption was found to be close a mechanical index of 0.3. Location of fluorescently labeled nanoparticles relative to blood vessels and tumor cells was determined in frozen sections using confocal microscopy. Tissue damage and FUS-induced changes at the cellular and molecular level were studied using histological and molecular techniques. In conclusion, the dual-frequency ultrasound transducer setup and our novel nanoparticle-microbubble platform showed promising results which will be used to develop a novel treatment of brain metastasis combining dual-frequency FUS with drug delivery using microbubbles. 1. Nanoparticle-stabilized microbubbles for multimodal imaging and drug delivery. Mørch Ý et al. Contrast Media Mol Imaging. 2015 Sep;10(5):356-66 2. Nanoparticle delivery to the brain - By focused ultrasound and self-assembled nanoparticle-stabilized microbubbles. Åslund AK et al. J Control Release. 2015 Oct 28;220(Pt A):287-294 3. Automated tracking of nanoparticle-labeled melanoma cells improves the predicted power of a brain metastasis model. Sundstrøm T et al. Cancer Res. 2013 Feb;73(8):2445-2456. Citation Format: Habib Baghirov, Andreas Åslund, Sofie Snipstad, Sigrid Berg, Rune Hansen, Frits Thorsen, Yrr Mørch, Catharina de Lange Davies. Focused ultrasound-mediated transport of poly(alkyl) cyanoacrylate nanoparticles across the blood-brain barrier in a melanoma brain metastasis model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2073.

Evaluation of inertial cavitation activity in tissue through measurement of oxidative stress

Ultrasound cavitation is an essential mechanism involved in the therapeutic local enhancement of drug delivery by ultrasound for cancer treatment. Inertial cavitation also triggers chemical reactions that generate free radicals and subsequent oxidative stress in the tissue. The aim of this study was to measure the oxidative stress induced by inertial cavitation in ex vivo tissue and to test the association between the exposure conditions and the oxidative stress.A confocal ultrasound setup was used to sonicate and create inertial cavitation in freshly excised adipose pig tissue. The ex vivo tissue samples were then processed to measure the quantity of malondialdehyde (MDA), an end-product of polyunsaturated free fatty acid oxidation. The creation of hydroxyterephthalic acid (HTA) from the reaction of terephthalic acid (TA) with free radicals in water was also quantified in vitro. Samples were sonicated for different durations using various amplitudes for the applied pressure.The results showed a minimum 2-fold increase in the amount of detected MDA in the sonicated tissue samples compared to baseline clearly suggesting the generation of free radicals by inertial cavitation. The method exhibited a moderate dependence of MDA generated upon the duration of exposure (R2=057,p<0.0001). The average increase in MDA concentration was approximately 2-fold, 5-fold, 6-fold, and 9-fold for exposure durations per unit of volume of 0.13, 0.17, 0.25, and 0.50s/mm3, respectively. The results showed no statistically significant dependence on the amplitude of the pressure within the used range. Both pressure amplitude and exposure duration, however, influenced the HTA concentration (R2>0.95,p<0.0001).This biochemical method can be used on ex vivo tissue to detect the generation of free radicals induced by inertial cavitation. In large enough sample populations, the cavitation activity is linked to the exposure conditions of the sonication.

Rheology over five orders of magnitude in model hydrogels: agreement between strain-controlled rheometry, transient elastography, and supersonic shear wave imaging.

Shear wave elastography helps physicians to characterize pathologies by assessing biomechanical properties of soft tissues. Compared with classical rheology, these techniques allow the quantification of the mechanical properties of tissues in the frequency range of hundreds of hertz. In this paper, ultrasound elastographic measurements and classical rheology are compared over a frequency range spanning five orders of magnitude [0.01 to 1200 Hz] to characterize model gels at multiple scales. Hybrid hydrogels were specially synthesized to get a fine tuning of the material dissipative response. Strain-controlled rheology (SCR) experiments were performed to get the elastic moduli G" and loss moduli G" from 0.01 Hz to 10 Hz and were confirmed by tensile tests. Transient elastography (TE from 50 to 400 Hz) and supersonic shear imaging (SSI from 200 to 1200 Hz) were used to characterize polymers at high frequency. Two different hydrogels were tested in the ultrasound setup with different concentration of scatterers. From low-frequency measurements, elastic moduli were extrapolated at high frequency and a very good correlation was obtained between SCR and TE and between SCR and SSI (r = 0.92 and r = 0.95, respectively). This paper demonstrates the capability of shear wave elastography to accurately image rheological properties of soft tissues, to differentiate soft elastic domains from viscous ones. It also gives new insights into soft material science because it provides a rheological tool in a high-frequency domain complementary to conventional rheometry.

Therapeutic efficacy of the combination of doxorubicin-loaded liposomes with inertial cavitation generated by confocal ultrasound in AT2 Dunning rat tumour model

The combination of liposomal doxorubicin (DXR) and confocal ultrasound (US) was investigated for the enhancement of drug delivery in a rat tumour model. The liposomes, based on the unsaturated phospholipid dierucoylphosphocholine, were designed to be stable during blood circulation in order to maximize accumulation in tumour tissue and to release drug content upon US stimulation. A confocal US setup was developed for delivering inertial cavitation to tumours in a well-controlled and reproducible manner. In vitro studies confirm drug release from liposomes as a function of inertial cavitation dose, while in vivo pharmacokinetic studies show long blood circulation times and peak tumour accumulation at 24–48 h post intravenous administration. Animals injected 6 mg kg−1 liposomal DXR exposed to US treatment 48 h after administration show significant tumour growth delay compared to control groups. A liposomal DXR dose of 3 mg kg−1, however, did not induce any significant therapeutic response. This study demonstrates that inertial cavitation can be generated in such a fashion as to disrupt drug carrying liposomes which have accumulated in the tumour, and thereby increase therapeutic effect with a minimum direct effect on the tissue. Such an approach is an important step towards a therapeutic application of cavitation-induced drug delivery and reduced chemotherapy toxicity.