Peak Negative Pressure Research Articles

Design of a low-cost pressure measurement device: validation and testing

Pressure measurement is essential in aerospace engineering. Measuring pressure allows us to understand the aerodynamic characteristics of the model. Consequently, it helps us propose an optimisation model design with high aerodynamic performance and low structure fatigues. However, the pressure measurement device is often complicated and costly. It is a big problem for developing countries to possess the device. This study proposes a simple and effective new pressure measurement device design. The device is sufficiently low cost, but it can provide high accuracy data as a commercial device. A calibration process was presented in a simple wind tunnel. Experiments are then conducted for measuring pressure distribution on NACA 2415 airfoil, and they are compared with the numerical data. The new pressure measurement device shows close results to the numerical data. A significantly low-pressure region is observed near the leading edge of the model. Additionally, when the angle of attack increases, the negative pressure peak increases its magnitude, both in numerical and simulation methods. The pressure measurement errors are less than 10%, and consequently, they can be applied for further study.

The Turbulence Intensity Effect on the Flow Characteristics and Aerodynamics of a Circular Cylinder

In this investigation, a numerical study about the turbulence intensity effect on the time-dependent flow structure around a circular cylinder employing k-ω based Detached Eddy Simulation (DES) turbulence model was performed at sub-critical Reynolds number of Re=5×103. According to the numerical analyses, the length of recirculation region reduces as the level of turbulence intensity augments. While the normalized length of recirculation region after the cylinder, Ls/D is measured as 1.225 at turbulence intensity of Tu=0.8%, it reduces to the value of Ls/D =1.0822 at turbulence intensity of Tu=7%. Furthermore, the location of peak negative pressure coefficient moves in downstream direction by increasing turbulence intensity. The drag coefficient, CD was observed to increase when turbulence intensity increases from Tu=0.8% to 7% and 12%. Thus, it was concluded that the level of turbulence intensity is effective on changing the flow characteristics and aerodynamics of a circular cylinder.

Improving temporal stability of stable cavitation activity of circulating microbubbles using a closed-loop controller based on pulse-length regulation

Stable cavitation (SC) has shown great potential for novel therapeutic applications. The spatiotemporal distribution of the SC activity of microbubbles circulating in a target region is not only correlated with the uniformity of treatment, but also with some undesirable effects. Therefore, it is important to achieve controllable and desirable SC activity in target regions for improved therapeutic efficiency and biosafety. This study proposes a closed-loop feedback controller based on pulse length (PL) regulation to improve the temporal stability of SC activity. Microbubbles circulating in a physiological flowing phantom were exposed to a 1 MHz focused transducer. The SC signals produced were initially received by another 7.5 MHz plane transducer, followed by high-speed signal acquisition and real-time processing. Based on the real-time-measured SC intensity excited by the current acoustic pulse, the proposed closed-loop feedback controller used three proportional coefficients to regulate the peak negative pressure (PNP) and PL of the next acoustic pulse during the acceleration and stable stages, respectively. The results show that the rise time and the temporal stability of the SC intensity of the microbubbles circulating in these two stages were improved significantly by the optimized proportional coefficients used in the proposed controller. Importantly, when compared with the traditional closed-loop feedback controller based on PNP regulation, the proposed closed-loop feedback controller based on PL regulation reduced the probability of a transition between stable and inertial cavitation, thus avoiding the risk of disadvantageous bioeffects in practical applications. These results demonstrate the effectiveness of the proposed PL-based closed-loop feedback controller and provide a feasible strategy for realization of controllable cavitation activity in applications.

Dual-Frequency Intravascular Sonothrombolysis: An In Vitro Study.

Thrombo-occlusive disease is one of the leading causes of death worldwide. There has been active research on safe and effective thrombolysis in preclinical and clinical studies. Recently, the dual-frequency transcutaneous sonothrombolysis with contrast agents [microbubbles (MBs)] has been reported to be more efficient in trigging the acoustic cavitation, which leads to a higher lysis rate. Therefore, there is increasing interest in applying dual-frequency technique for more significant efficacy improvement in intravascular sonothrombolysis since a miniaturized intravascular ultrasound transducer typically has a limited power output to fully harness cavitation effects. In this work, we demonstrated this efficacy enhancement by developing a new broadband intravascular transducer and testing dual-frequency sonothromblysis in vitro. A broadband intravascular transducer with a center frequency of 750 kHz and a footprint size of 1.4 mm was designed, fabricated, and characterized. The measured -6-dB fractional bandwidth is 68.1%, and the peak negative pressure is 1.5 MPa under the driving voltage of 80 Vpp. By keeping one frequency component at 750 kHz, the second frequency component was selected from 450 to 650 kHz with an interval of 50 kHz. The in vitro sonothrombolysis tests were conducted with a flow model and the results indicated that the MB-mediated, dual-frequency (750+500 kHz) sonothrombolysis yields an 85% higher lysis rate compared with the single-frequency treatment, and the lysis rate of dual-frequency sonothrombolysis increases with the difference between the two frequency components. These findings suggest a dual-frequency excitation technique for more efficient intravascular sonothrombolysis than conventional single-frequency excitation.

Repeated Acoustic Vaporization of Perfluorohexane Nanodroplets for Contrast-Enhanced Ultrasound Imaging.

Superheated perfluorocarbon nanodroplets are emerging ultrasound imaging contrast agents that boast biocompatible components, unique phase-change dynamics, and therapeutic loading capabilities. Upon exposure to a sufficiently high-intensity pulse of acoustic energy, the nanodroplet's perfluorocarbon core undergoes a liquid-to-gas phase change and becomes an echogenic microbubble, providing ultrasound contrast. The controllable activation leads to high-contrast images, while the small size of the nanodroplets promotes longer circulation times and better in vivo stability. One drawback, however, is that the nanodroplets can only be vaporized a single time, limiting their versatility. Recently, we and others have addressed this issue by using a perfluorohexane core, which has a boiling point above body temperature. Thus after vaporization, the microbubbles recondense back into their stable nanodroplet form. Previous work with perfluorohexane nanodroplets relied on optical activation via pulsed laser absorption of an encapsulated dye. This strategy limits the imaging depth and temporal resolution of the method. In this study, we overcome these limitations by demonstrating acoustic droplet vaporization with 1.1-MHz high-intensity focused ultrasound (HIFU). A short-duration, high-amplitude pulse of focused ultrasound provides a sufficiently strong peak negative pressure to initiate vaporization. A custom imaging sequence was developed to enable the synchronization of a HIFU transducer and a linear array imaging transducer. We show a visualization of repeated acoustic activation of perfluorohexane nanodroplets in polyacrylamide tissue-mimicking phantoms. We further demonstrate the detection of hundreds of vaporization events from individual nanodroplets with activation thresholds well below the tissue cavitation limit. Overall, this approach has the potential to result in reliable and repeatable contrast-enhanced ultrasound imaging at clinically relevant depths.

Abstract 12472: Development of an in vitro System to Study Mechanisms of Ultrasound-Targeted Microbubble Cavitation-Mediated Blood Brain Barrier Opening

Introduction: Ultrasound-targeted microbubble cavitation ( UTMC ) is being explored as a method to transiently open the blood brain barrier ( BBB ). While UTMC-mediated BBB opening is a promising avenue for increasing drug delivery to the central nervous system, its underlying mechanisms are incompletely understood. We sought to develop an in vitro system simulating cerebral endothelial barrier function, to facilitate studies aimed at exploring mechanisms of UTMC-mediated BBB opening. Methods: We developed a transwell model with murine brain microvasculature endothelial cells (bEnd.3) and rat C6 glioma cells on opposite sides of a support membrance. Three concentrations of lipid microbubbles ( MB ) were added before applying pulsed ultrasound (1 MHz, 10 μs pulse duration, 10 ms pulse interval) at 3 peak negative pressures ( PNP ) for 20 s. Endothelial barrier function was assessed using transendothelial electrical resistance ( TEER ) and permeability using 10 kDa Texas Red dextran. Cells were stained with Hoechst (nucleus), CellMask Deep Red (cell coverage), calcein-AM (viability), and propidium iodide ( PI ; sonoporation) Differences between experimental conditions were compared using unpaired 2-tailed t-test. Significance was defined as p <0.05. Results: At a given MB:cell ratio, higher PNPs increased the percent of viably sonoporated cells ( Fig 1A ), but caused increasing cell loss from the transwell (decrease in % area coverage) at PNP greater than 250kPa and MB:cell ratio higher than 3:1 ( Fig 1B ). Therefore, 250kPa ultrasound and 3:1 MB ratio were used in the permeability studies: BBB permeability increased by 15 min after UTMC as measured by TEER ( Fig 1C ) and dextran flux ( Fig 1D ), but recovered 1 hour later. Conclusions: We developed a co-culture transwell model of the BBB to simulate UTMC-induced reversible endothelial barrier hyperpermeability. This model will uniquely allow systematic investigation of mechanisms of UTMC-mediated BBB opening.

Abstract 13414: Studying Sonoporation-Induced Drug Payload Penetration Beyond the Blood-Brain Barrier Using Multi-Cellular Human Brain Spheroids

Introduction: Ultrasound-targeted microbubble cavitation ( UTMC ) facilitates delivery of cell-impermeant drugs across the endothelial barrier, such as the blood brain barrier ( BBB ) . Using cultured endothelial cell ( EC ) monolayers, we reported that UTMC causes sonoporation and inter-endothelial gaps, which may mediate vascular hyperpermeability, although mechanisms are incompletely understood. Further, the effects of UTMC on extravascular cells, and extent of payload penetration are unknown, as the monolayer does not recapitulate the 3D multicellular environment. Here, we established a 3D multicellular human brain spheroid model to study UTMC bioeffects and underlying mechanisms. Methods: Spheroids were generated using neurons and astrocytes derived from human iPSCs, primary human brain- microglia, ECs and pericytes, and placed in a water tank with lipid microbubbles ( MBs ). Ultrasound (1 MHz frequency, 250-500 kPa peak negative pressures, 10 μs pulse duration, 10 ms pulse interval) was delivered for 20 s and spheroids were immediately collected. Immunostaining was used to localize cell types; propidium iodide (PI) uptake to mark sonoporation; calcein-AM and sytox to detect cell viability; and Texas red dextran (TRD) (10 kDa) to quantify permeability, using confocal microscopy. Results: Immunostaining showed ECs and pericytes at the spheroid periphery, with high expression of membranous ZO-1. BBB functionality was confirmed with histamine treatment, which increased permeability to TRD (28.8% increase in TRD mean intensity, p =0.0015). Interestingly, PI uptake (sonoporation) occurred in cells beyond the BBB. TRD penetrated up to ~100 μm beyond the BBB upon UTMC (12.2% increase). Inhibition of endothelial nitric oxide synthase with L-NAME reduced UTMC-induced TRD penetration (19% decrease, p =0.0458). Conclusions: In this novel 3D human brain spheroid model with intact BBB, UTMC caused nitric-oxide dependent BBB breach. Moreover, this is the first report of UTMC causing “remote” sonoporation of cells not in direct contact with MBs, which bears further study. Our model allows the study of mechanisms mediating UTMC efficacy for targeted delivery of drugs across the endothelial barrier, which should facilitate its clinical translation.

Miniaturized acoustic focus tunable photoacoustic transmitter probe

Aiming to provide dynamically adjustable acoustic field for in vivo ultrasound application scenarios, a miniaturized optical fiber photoacoustic (PA) transmitter is presented. Different from the existing laser generated focused ultrasound probes with fixed acoustic focal length, its focus can be continuously adjusted from infinity to 2.166 mm by deforming the PA conversion film using pneumatic actuation method. The PA film is designed into a circular suspending elastic membrane structure with clamped boundary, which consists of a PDMS/candle soot nanoparticles (CSNPs) mixture layer sandwiched between two pure polydimethylsiloxane (PDMS) layers. Using soft lithography strategy, the PA film together with a structured PDMS substrate and a multimode fiber (MMF) are assembled together to construct the final PA probe with 2.68 mm aperture. For a proof-of-concept demonstration, three different focusing statuses (with 5.196 mm, 3.246 mm and 2.166 mm focal lengths) are provided and their axial acoustic field distributions are characterized as well. Under the excitation condition with the laser fluence of 13.26 mJ/cm2, acoustic signal with 9 MHz center frequency, 92.91% fractional bandwidth at − 6 dB and peak negative pressure (PNP) amplitude up to 8.91 MPa at the 2.166 mm focal point can be achieved, resulting in mechanical index (MI) of 2.97. Referring to the reported data, the current PA transmitter probe demonstrates excellent application potential.

Improved Sensitivity of Ultrasound-Based Subharmonic Aided Pressure Estimation Using Monodisperse Microbubbles.

Subharmonic aided pressure estimation (SHAPE) has been shown effective for noninvasively measuring hydrostatic fluid pressures in a variety of clinical applications. The objective of this study was to explore potential improvements in SHAPE sensitivity using monodisperse microbubbles. Populations of monodisperse microbubbles were created using a commercially available microfluidics device (Solstice Pharmaceuticals). Size distributions were assessed using a Coulter Counter and stability of the distribution following fabrication was evaluated over 24 hours. Attenuation of the microbubble populations from 1 to 10 MHz was then quantified using single element transducers to identify each formulation's resonance frequency. Frequency spectra over increasing driving amplitudes were investigated to determine the nonlinear phases of subharmonic signal generation. SHAPE sensitivity was evaluated in a hydrostatic pressure-controlled water bath using a Logiq E10 scanner (GE Healthcare). Monodisperse lipid microbubble suspensions ranging from 2.4 to 5.3 μm in diameter were successfully created and they showed no discernable change in size distribution over 24 hours following activation. Calculated resonance frequencies ranged from 2.1 to 6.3 MHz and showed excellent correlation with microbubble diameter (R2 > 0.99). When investigating microbubble frequency response, subharmonic signal occurrence was shown to begin at 150 kPa peak negative pressure, grow up to 225 kPa, and saturate at approximately 250 kPa. Using the Logiq E10, monodisperse bubbles demonstrated a SHAPE sensitivity of -0.17 dB/mmHg, which was nearly twice the sensitivity of the commercial polydisperse microbubble currently being used in clinical trials. Monodisperse microbubbles have the potential to greatly improve the sensitivity of SHAPE for the noninvasive measurement of hydrostatic pressures.

Effect of pulse duration and repetition rate on burst wave lithotripsy stone fragmentation in vitro

Burst wave lithotripsy (BWL) is a noninvasive technology to fragment urinary stones using short pulses of focused ultrasound. The aim of this study was to assess how different combinations of pulse length and pulse repetition frequency (PRF) impact stone fragmentation rate and cavitation activity in an in vitro-model. Human calcium oxalate stones between 4–7mm were exposed in a tissue phantom with a 350-kHz BWL transducer with a beamwidth of 6 mm. Treatments were delivered in a 45–50% degassed water bath. Ultrasound imaging was used to target the stone and monitor cavitation activity around the stone. Stones were exposed to ten different parameter sets at peak negative pressure = 6.2 MPa in 5-min intervals up to 30 min total. After each interval, the remaining mass of fragments >2mm was measured to determine the rate of comminution. Longer pulse duration generally produced improved fragmentation. Increasing the pulse repetition rate with set pulse duration did not always produce faster comminution. The results suggest that more effective fragmentation may be achieved in BWL by long pulse durations and low PRF. [Work funded by NIDDK, Grants P01 DK043881 and K01 DK104854. Maxwell, Cunitz, and Bailey have consulting agreements with and equity in SonoMotion, Inc.]

Progression of hemorrhagic kidney injury from burst wave lithotripsy exposures

Burst wave lithotripsy (BWL) is a new non-invasive treatment for comminuting kidney stones. Although exposure parameters used in current clinical trials have produced negligible renal injury in preclinical pig studies, it remains of interest to understand how quickly injury accumulates, should it occur. BWL treatments lasting ≤30 min were delivered to 36 sites in 20 kidneys of 11 pigs. Treatments at 350 kHz utilized pulses with supra-clinical 8–9 MPa peak negative pressure, 20 cycles/pulse, and a pulse repetition frequency (PRF) of 10 or 40 Hz. Real-time monitoring was performed with B-mode and Doppler ultrasound to identify the presence and duration of cavitation activity, which has been correlated with the onset of injury. After treatment, kidneys were excised for magnetic resonance imaging (MRI) within 3 h of euthanasia. MRI was used to quantify the volume of any hemorrhagic injury. For sites with injury at 40 Hz PRF, the average (n = 5) injury volume increased with the number of BWL pulses (72, 720, 7200, or 72 000 pulses) delivered with cavitation. Notably, the rate of lesion growth slowed above 7200 pulses while all lesion volumes were smaller for equivalent cavitation exposures at 10 Hz PRF. [Funding support by NIH P01-DK043881, K01-DK104854.]

Preliminary report on the functional changes associated with burst wave lithotripsy treated pig kidneys

Burst Wave Lithotripsy (BWL) is a new stone treatment that utilizes ultrasound to fracture renal calculi. However, it is not known if BWL alters renal function, so we tested if a clinical dose of BWL impacts glomerular filtration rate (GFR) or kidney blood flow. Treatment consisted of placing each pig (32–42 kg) on its side, locating the lower pole of the right kidney, and treating that kidney with a BWL dose of 18,000 ultrasound pulses at 10Hz, 20 cycles/pulse and a peak negative pressure of −7 MPa (n = 6). Six additional pigs were used as sham controls. Inulin and para-aminohippuric acid (PAH) were infused into the pigs with blood and urine samples being collected both before and 1-h after BWL treatment. The concentrations of inulin and PAH were determined in the samples and used to calculate GFR and effective renal plasma flow (eRPF). For the BWL treated group, GFR and eRPF did not change after BWL exposure (−6.7 ± 7.2% for GFR, −10.9 ± 5.5% for eRPF), and this response was like the sham control group ( P = 0.23 for GFR, P = 0.08 for eRPF). A typical clinical dose of BWL caused no change in renal function. [Work supported by NIH, Grant P01 DK43881.]

Unsupported gold nanocones as sonocatalytic agents with enhanced catalytic properties

Gold catalysts have attracted attention for enabling sustainable chemical processes under ambient conditions. This reactivity is attributed to the small size of the catalysts (<5 nm); however, their size also creates difficulty when removing from product streams and often require rare-metal additives to enhance reaction rate kinetics, thereby limiting the environmental benefits of these catalysts. Comparatively, submicron gold catalysts are easier to separate but are much less reactive under ambient conditions. In this study, we synthesized submicron gas-stabilising gold nanocones (gs-AuNCs) that are acoustically responsive to afford greater reaction rates than other conventional gold catalysts. We explore the catalytic performance of acoustically responsive gs-AuNCs exposed to focussed ultrasound at 5.0 MPa peak negative pressure and 1.1 MHz center frequency. Cavitation nucleated from gs-AuNCs significantly increased the sonocatalytic degradation of water pollutants without the need for co-catalysts. The ability to amplify catalysis with ultrasound by tailoring the morphology of the catalyst to control cavitation opens new paths for future designs of sonocatalysts that may enable a sustainable chemical approach needed for a broad range of industrial processes.

Ultrasound Molecular Imaging for the Guidance of Ultrasound-Triggered Release of Liposomal Doxorubicin and Its Treatment Monitoring in an Orthotopic Prostatic Tumor Model in Rat

Liposome encapsulation of drugs is an interesting approach in cancer therapy to specifically release the encapsulated drug at the desired treatment site. In addition to thermo-, pH-, light-, enzyme- or redox-responsive liposomes, which have had promising results in (pre-) clinical studies, ultrasound-triggered sonosensitive liposomes represent an exciting alternative to locally trigger the release from these cargos. Localized drug release requires precise tumor visualization to produce a targeted and ultrasound stimulus. We used ultrasound molecular imaging (USMI) with BR55, a vascular endothelial growth factor receptor 2 (VEGFR2)-targeted ultrasound contrast agent, to guide ultrasound-triggered release of sonosensitive liposomes encapsulating doxorubicin (L-DXR) in an orthotopic prostatic rodent tumor model. Forty-eight hours after L-DXR injection, local release of doxorubicin was triggered with a confocal ultrasound device with two focused transducers, 1.1-MHz center frequency, and peak positive and negative pressures of 20.5 and 13 MPa at focus. Tumor size decreased by 20% in 2 wk with L-DXR alone (n = 9) and by 70% after treatment with L-DXR and confocal ultrasound (n = 7) (p < 0.01). The effect of doxorubicin on perfusion/vascularity and VEGFR2 expression was evaluated by USMI and immunohistochemistry of CD31 and VEGFR2 and did not reveal differences in perfusion or VEGFR2 expression in the absence or after the triggered release of liposomes. USMI can provide precise guidance for ultrasound-triggered release of liposomal doxorubicin mediated by a confocal ultrasound device; moreover, the combination of B-mode imaging and USMI can help to follow the response of the tumor to the therapy.

Dual-Use Transducer for Ultrasound Imaging and Pulsed Focused Ultrasound Therapy.

Pulsed focused ultrasound (pFUS) uses short acoustic pulses delivered at low duty cycle and moderate intensity to noninvasively apply mechanical stress or introduce disruption to tissue. Ultrasound-guided pFUS has primarily been used for inducing cavitation at the focus, with or without contrast agents, to promote drug delivery to tumors. When applied in tandem with contrast agents, pFUS is often administered using an ultrasound imaging probe, which has a small footprint and does not require a large acoustic window. The use of nonlinear pFUS without contrast agents was recently shown to be beneficial for localized tissue disruption, but required higher ultrasound pressure levels than a conventional ultrasound imaging probe could produce. In this work, we present the design of a compact dual-use 1-MHz transducer for ultrasound-guided pFUS without contrast agents. Nonlinear pressure fields that could be generated by the probe, under realistic power input, were simulated using the Westervelt equation. In water, fully developed shocks of 42-MPa amplitude and peak negative pressure of 8 MPa were predicted to form at the focus at 458-W acoustic power or 35% of the maximum reachable power of the transducer. In absorptive soft tissue, fully developed shocks formed at higher power (760 W or 58% of the maximum reachable power) with the shock amplitude of 33 MPa and peak negative pressure of 7.5 MPa. The electronic focus-steering capabilities of the array were evaluated and found to be sufficient to cover a target with dimensions of 19 mm in axial direction and 44 mm in transversal direction.

Modeling the Physics of Bubble Nucleation in Histotripsy.

This work aims to establish a theoretical framework for the modeling of bubble nucleation in histotripsy. A phenomenological version of the classical nucleation theory was parametrized with histotripsy experimental data, fitting a temperature-dependent activity factor that harmonizes theoretical predictions and experimental data for bubble nucleation at both high and low temperatures. Simulations of histotripsy pressure and temperature fields are then used in order to understand spatial and temporal properties of bubble nucleation at varying sonication conditions. This modeling framework offers a thermodynamic understanding on the role of the ultrasound frequency, waveforms, peak focal pressures, and duty cycle on patterns of ultrasound-induced bubble nucleation. It was found that at temperatures lower than 50 °C, nucleation rates are more appreciable at very large negative pressures such as -30 MPa. For focal peak-negative pressures of -15 MPa, characteristic of boiling histotripsy, nucleation rates grow by 20 orders of magnitude in the temperature interval 60 °C-100 °C.

Experimental study of train-induced pressure acting on the platform screen doors in subway station

The pressure transient on a platform screen door (PSD) is crucial for its structural safety and proper operation. This study experimentally investigated the train-induced pressure on the PSDs in a typical subway station using a moving model test system. Two typical cases were tested: the non-stop and chasing cases. In the non-stop case, the train passes through the station without stopping. In the chasing case, the train runs towards the station through the tunnel, while another train stops at the station. The train-induced pressure inside the tunnel was also tested for comparison. It was found that the train generated a compression wave when it passed the ventilation shaft of the tunnel, which was similar to that occurring when it entered the tunnel. In the non-stop case, the PSDs experienced two positive and one negative pressure peaks during the entire process. The first positive peak was dominated by the pressure wave transmitted through the tunnel; the second positive peak occurred when the train head reached the PSDs. A negative pressure peak occurred when the train tail passed by. In the chasing case, even when the incoming train was far away from the station, its pressure wave resulted in significant pressure on the PSDs, which may be the reason why the PSDs cannot open properly during rush hours.

Histotripsy Ablation of Bone Tumors: Feasibility Study in Excised Canine Osteosarcoma Tumors

Osteosarcoma (OS) is a primary bone tumor affecting both dogs and humans. Histotripsy is a non-thermal, non-invasive focused ultrasound method using controlled acoustic cavitation to mechanically disintegrate tissue. In this study, we investigated the feasibility of treating primary OS tumors with histotripsy using a 500-kHz transducer on excised canine OS samples harvested after surgery at the Veterinary Teaching Hospital at Virginia Tech. Samples were embedded in gelatin tissue phantoms and treated with the 500-kHz histotripsy system using one- or two-cycle pulses at a pulse repetition frequency of 250 Hz and a dosage of 4000 pulses/point. Separate experiments also assessed histotripsy effects on normal canine bone and nerve using the same pulsing parameters. After treatment, histopathological evaluation of the samples was completed. To determine the feasibility of treating OS through intact skin/soft tissue, additional histotripsy experiments assessed OS with overlying tissues. Generation of bubble clouds was achieved at the focus in all tumor samples at peak negative pressures of 26.2 ± 4.5 MPa. Histopathology revealed effective cell ablation in treated areas for OS tumors, with no evidence of cell death or tissue damage in normal tissues. Treatment through tissue/skin resulted in generation of well-confined bubble clouds and ablation zones inside OS tumors. Results illustrate the feasibility of treating OS tumors with histotripsy.

Evaluation of a mechanical lung model to test small animal whole body plethysmography

Whole-body plethysmography (WBP) is an established method to determine physiological parameters and pathophysiological alteration of breathing in animals and animal models of a variety of diseases. Although frequently used, there is ongoing debate about what exactly is measured by whole-body-plethysmography and how reliable the data derived from this method are. Here, we designed an artificial lung model that enables a thorough evaluation of different predictions about and around whole-body plethysmography. Using our lung model, we confirmed that during WBP two components contribute to the pressure changes detected in the chamber: (1) the increase in the pressure due to heating and moistening of the air during inspiration, termed conditioning; (2) changes in the chamber pressure that depend on airway resistance. Both components overlap and contribute to the temporal pressure-profile measured in the chamber or across the wall of the chamber, respectively. Our data showed that a precise measurement of the breathing volume appears to be hindered by at least two factors: (1) the unknown relative contribution of each of these two components; (2) not only the air in the inspired volume is conditioned during inspiration, but also air within the residual volume and dead space that is recruited during inspiration. Moreover, our data suggest that the expiratory negative pressure peak that is used to determine the enhanced pause (Penh) parameter is not a measure for airway resistance as such but rather a consequence of the animal’s response to the airway resistance, using forced or active expiration to overcome the resistance by a higher thoracic pressure.

Control of the dynamics of a boiling vapour bubble using pressure-modulated high intensity focused ultrasound without the shock scattering effect: A first proof-of-concept study

Boiling histotripsy is a promising High-Intensity Focused Ultrasound (HIFU) technique that can be used to induce mechanical tissue fractionation at the HIFU focus via cavitation. Two different types of cavitation produced during boiling histotripsy exposure can contribute towards mechanical tissue destruction: (1) a boiling vapour bubble at the HIFU focus and (2) cavitation clouds in between the boiling bubble and the HIFU source. Control of the extent and degree of mechanical damage produced by boiling histotripsy is necessary when treating a solid tumour adjacent to normal tissue or major blood vessels. This is, however, difficult to achieve with boiling histotripsy due to the stochastic formation of the shock scattering-induced inertial cavitation clouds. In the present study, a new histotripsy method termed pressure-modulated shockwave histotripsy is proposed as an alternative to or in addition to boiling histotripsy without inducing the shock scattering effect. The proposed concept is (a) to generate a boiling vapour bubble via localised shockwave heating and (b) subsequently control its extent and lifetime through manipulating peak pressure magnitudes and a HIFU pulse length. To demonstrate the feasibility of the proposed method, bubble dynamics induced at the HIFU focus in an optically transparent liver tissue phantom were investigated using a high speed camera and a passive cavitation detection systems under a single 10, 50 or 100 ms-long 2, 3.5 or 5 MHz pressure-modulated HIFU pulse with varying peak positive and negative pressure amplitudes from 5 to 89 MPa and −3.7 to −14.6 MPa at the focus. Furthermore, a numerical simulation of 2D nonlinear wave propagation with the presence of a boiling bubble at the focus of a HIFU field was conducted by numerically solving the generalised Westervelt equation. The high speed camera experimental results showed that, with the proposed pressure-modulated shockwave histotripsy, boiling bubbles generated by shockwave heating merged together, forming a larger bubble (of the order of a few hundred micron) at the HIFU focus. This coalesced boiling bubble then persisted and maintained within the HIFU focal zone until the end of the exposure (10, 50, or 100 ms). Furthermore, and most importantly, no violent cavitation clouds which typically appear in boiling histotripsy occurred during the proposed histotripsy excitation (i.e. no shock scattering effect). This was likely because that the peak negative pressure magnitude of the backscattered acoustic field by the boiling bubble was below the cavitation cloud intrinsic threshold. The size of the coalesced boiling bubble gradually increased with the peak pressure magnitudes. In addition, with the proposed method, an oval shaped lesion with a length of 0.6 mm and a width of 0.1 mm appeared at the HIFU focus in the tissue phantom, whereas a larger lesion in the form of a tadpole (length: 2.7 mm, width: 0.3 mm) was produced by boiling histotripsy. Taken together, these results suggest that the proposed pressure-modulated shockwave histotripsy could potentially be used to induce a more spatially localised tissue destruction with a desired degree of mechanical damage through controlling the size and lifetime of a boiling bubble without the shock scattering effect.