Short Acoustic Pulses Research Articles

Acoustic cavitation localization during histotripsy using transmit-receive capable arrays

The nucleation and collapse of cavitation generated during histotripsy results in point-like emissions of shockwaves. Owing to the short duration acoustic pulses utilized during histotripsy the acoustic background from pulse reflections off intervening tissues is minimal and temporally isolated. This allows acoustic cavitation emission (ACE) shockwaves to be differentiated from the background in measured signals using simplified approaches such as peak detection and time gating, even in signals acquired using narrow bandwidth receivers such as the transmitting elements of the histotripsy array. The array elements allow acquisitions from across the array's entire aperture, which in turn allows cavitation to be localized in 3D. Here we describe multiple methods for localizing cavitation and evaluating induced tissue damage based on ACE signals measured using transmit-receive capable histotripsy arrays. The speed and accuracy of the methods were evaluated in ex vivo and in vitro experiments. Cavitation could be localized in 3D at rates >100Hz. Mean localization errors, with respect to measurements from optical images, were <2 mm (approximately the diameter of the generated bubbles). Cavitation lifespans could be assessed concurrently with the bubbles' 3D locations and correlated well with histological observations of induced damage, allowing 3D assessments of damage.

Acoustic responses of underwater superhydrophobic surfaces subjected to an intense pulse

Underwater stability of an air layer trapped in a micro-structure, plastron, is critical in drag reduction applications. Here, we investigate the wetting state and plastron stability of underwater superhydrophobic surfaces (SHS) under an intense acoustic drive. Flat surfaces and SHS are subjected to short acoustic pulses of different intensities. At low amplitude, the comparison between the results of various surfaces shows that plastron behaves like a water–air interface, whose presence can be detected from the phase of the reflected acoustic waves. At moderate intensity, a wetting transition towards a completely wetting state is observed and shown to be triggered by a sufficiently large acoustic radiation pressure. This wetting transition is well captured by a simplified model by balancing radiation pressure with the critical capillary pressure for the interface sliding. Cavitation clouds appear under strong excitation; their sizes and positions greatly depend on the surface acoustic boundary condition. For SHS in a Cassie–Baxter state (with an air layer), cavitation clouds appear at specific locations (from the solid surface) corresponding to the pressure anti-node of the transient standing wave generated by the reflection. This study unprecedentedly demonstrates the capability of acoustic waves to monitor and characterize plastron stability with low and moderate amplitudes, respectively.

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.

Acoustically Detonated Microbubbles Coupled with Low Frequency Insonation: Multiparameter Evaluation of Low Energy Mechanical Ablation.

Noninvasive ultrasound surgery can be achieved using focused ultrasound to locally affect the targeted site without damaging intervening tissues. Mechanical ablation and histotripsy use short and intense acoustic pulses to destroy the tissue via a purely mechanical effect. Here, we show that coupled with low-frequency excitation, targeted microbubbles can serve as mechanical therapeutic warheads that trigger potent mechanical effects in tumors using focused ultrasound. Upon low frequency excitation (250 kHz and below), high amplitude microbubble oscillations occur at substantially lower pressures as compared to higher MHz ultrasonic frequencies. For example, inertial cavitation was initiated at a pressure of 75 kPa for a center frequency of 80 kHz. Low frequency insonation of targeted microbubbles was then used to achieve low energy tumor cell fractionation at pressures below a mechanical index of 1.9, and in accordance with the Food and Drug Administration guidelines. We demonstrate these capabilities in vitro and in vivo. In cell cultures, cell viability was reduced to 16% at a peak negative pressure of 800 kPa at the 250 kHz frequency (mechanical index of 1.6) and to 10% at a peak negative pressure of 250 kPa at a frequency of 80 kHz (mechanical index of 0.9). Following an intratumoral injection of targeted microbubbles into tumor-bearing mice, and coupled with low frequency ultrasound application, significant tumor debulking and cancer cell death was observed. Our findings suggest that reducing the center frequency enhances microbubble-mediated mechanical ablation; thus, this technology provides a unique theranostic platform for safe low energy tumor fractionation, while reducing off-target effects.

Combining Mechanical High-Intensity Focused Ultrasound Ablation with Chemotherapy for Augmentation of Anticancer Immune Responses.

As a noninvasive therapy, high-intensity focused ultrasound (HIFU) shows great potential in inducing anticancer immune responses. However, the overall anticancer efficacy of HIFU is still limited due to the rapid attenuation of ultrasound waves and inadequacy of ultrasound waves to spread to the whole tumor. Here, we combined HIFU with the ultrasound contrast agent/chemotherapeutic drug co-delivery nanodroplets to achieve synergistic enhancement of anticancer efficacy. Different from the widely used thermal HIFU irradiation, by which excessive heating would result in inactivation of immune stimulatory molecules, we used short acoustic pulses to trigger HIFU (mechanical HIFU, mHIFU) to improve anticancer immune responses. The nanodroplets displayed a mHIFU/glutathione (GSH)-dual responsive drug release property, and their cellular uptake efficacy and toxicity against cancer cells increased upon mHIFU irradiation. The generated immunogenic debris successfully induced the exposure of damage-associated molecular patterns on the cell surface for dendritic cells (DCs) maturation. In vivo experiments with tumor-bearing mice showed that the co-delivery nanodroplets in combination with mHIFU could effectively inhibit tumor growth by inducing immunogenic cell death, activating DCs maturation, and enhancing the effector T-cell infiltration within tumors. This work reveals that combined treatment with nanodroplets and mHIFU is a promising approach to eradicate tumors.

Bayesian Machine Learning for the Prognosis of Combustion Instabilities From Noise

Abstract Experiments are performed on a turbulent swirling flame placed inside a vertical tube whose fundamental acoustic mode becomes unstable at higher powers and equivalence ratios. The power, equivalence ratio, fuel composition, and boundary condition of this tube are varied and, at each operating point, the combustion noise is recorded. In addition, short acoustic pulses at the fundamental frequency are supplied to the tube with a loudspeaker and the decay rates of subsequent acoustic oscillations are measured. This quantifies the linear stability of the system at every operating point. Using this data for training, we show that it is possible for a Bayesian ensemble of neural networks to predict the decay rate from a 300 ms sample of the (unpulsed) combustion noise and therefore forecast impending thermoacoustic instabilities. We also show that it is possible to recover the equivalence ratio and power of the flame from these noise snippets, confirming our hypothesis that combustion noise indeed provides a fingerprint of the combustor's internal state. Furthermore, the Bayesian nature of our algorithm enables principled estimates of uncertainty in our predictions, a reassuring feature that prevents it from making overconfident extrapolations. We use the techniques of permutation importance and integrated gradients to understand which features in the combustion noise spectra are crucial for accurate predictions and how they might influence the prediction. This study serves as a first step toward establishing interpretable and Bayesian machine learning techniques as tools to discover informative relationships in combustor data and thereby build trustworthy, robust, and reliable combustion diagnostics.

Assessment of the Acoustic Reflectometry Technique to Detect Pipe Blockages

Abstract Flow assurance is an important aspect of deepwater pipeline design and operation since one of the critical issues is the eventual initiation and growth of hydrate or paraffin blockages under certain conditions. Another relevant problem is the incidence of inorganic scale deposition in oil well production tubes during operation. Offshore operators can obtain enormous benefits if information regarding the position and extent of an eventual blockage is available since mitigation measures can be optimized. This work deals with experimental and numerical simulations of an acoustic system to identify and measure blockages. The technique uses a short duration acoustic pulse that is injected into the pipe. When the pulse encounters an impedance discontinuity, a portion is reflected toward the acoustic source. The analysis of the measured signal reflections can provide valuable data related to the location and size of the blockages. An experimental setup with a steel pipe of 4 in. internal diameter and length of 100 m was developed to evaluate the suitability of the technique for gas pipelines. In parallel, finite element analyses were performed using the commercial software abaqus to simulate the same physical parameters. The experiments were numerically reproduced with good correlation proving the potential of the technique. Subsequently, a parametric study was carried out to examine the acoustic detection capability using different blockage types. Finally, a prototype of the acoustic reflectometry detection system was developed and tested in a full-scale onshore water-filled pipeline to show the feasibility of the method for detecting blockages.

Forward Stimulated Brillouin Scattering Analysis of Optical Fibers Coatings

The proper function of protective coating layers is essential for the handling and application of brittle optical fibers. The elastic parameters of polymer coatings can be studied through off-line analysis of test samples. However, the monitoring of these properties on a working fiber during service is challenging. In this work, we use forward stimulated Brillouin scattering processes in standard single mode fibers to measure the acoustic velocity in several types of coating layers. Pump light launches short acoustic pulses outward from the core of the fiber. Multiple reflections at the boundaries between cladding and coating, and between coating and air, form a series of delayed acoustic echoes across the core. These echoes are monitored, in turn, by photo-elastic phase modulation of probe light. Data are collected at temperatures between 25-120 °C. The thermal dependence of the acoustic velocities in several coatings and of the F-SBS resonance frequencies is investigated. Observations are corroborated by calculations. The proposed technique is well suited for research and development of coating materials, production line quality control, reliability studies and preventive maintenance of working fibers.

Strain-Induced Luminescence of a Composite Material Based on Polymethyl Methacrylate and a Fine Powder of a Phosphor

A mechanoluminescent layer of a composite material based on a polymer of polymethyl methacrylate and a fine powder of phosphor SrAl2O4:(Eu2+,Dy3+) on the surface of polymethyl methacrylate is obtained. The mechanoluminescence of the composite layer under the action of short acoustic pulses and a mechanical impactor is studied. It is shown the composite layer has high efficiency of the mechanical-to-optical conversion.

Mechanoluminescence of a composite based on polymethylmethacrylate and fine-disperse powder of phosphor excited by short acoustic pulses and dynamic action of the stylus

A composite mechanoluminescent layer has been produced on the surface of polymethylmethacrylate by liquid-phase embedding of [Formula: see text] phosphor microparticles into the polymethylmethacrylate surface layer. The photoluminescence and mechanoluminescence of the obtained layer have been investigated. The mechanoluminescence was excited by the short acoustic pulses and by the dynamic pressure of the stylus sliding over the mechanoluminescent layer surface. A possible mechanism of mechanoluminescence excitation is under discussion. The produced composite layer is shown to exhibit high efficiency of “mechano-optical” transformation.

Mechanoluminescence of composite layer applied on polymer surface excited by short acoustic pulses in water

A composite mechanoluminescent layer has been produced on the surface of polymethylmethacrylate by liquid-phase embedding of SrAl2O4:(Eu2+, Dy3+) phosphor microparticles into the polymethylmethacrylate surface layer. The photoluminescence and mechanoluminescence of the obtained layer have been investigated. The mechanoluminescence was excited by the short acoustic pulses. A possible mechanism of mechanoluminescence excitation is under discussion. The produced composite layer is shown to exhibit high efficiency of “mechano-optical” transformation.

On the reducing of the acoustic signal length from the piezoelectric transducers of the sea ice monitoring systems

The solution of navigation problems the ice situation problems in the Arctic region need to study the acoustic parameters and local reflective properties of ice in real conditions. Information about the local sea ice acoustic properties essentially helps to solve the problems of statistical forecasting of reflective and scattering properties of ice cover. The successful solution of these problems mostly depends on the metrological parameters of the probing signals emitted by the primary piezoelectric transducers. This means, that to increase the resolution of the control and measuring equipment it is better to radiate and to receive short acoustic pulses. The article presents the results of analysis the pulse mode of operation of cylindrical piezoelectric transducers designed to measure the velocity of sound in sea ice. To reduce the length of acoustic pulses, an inductive-resistive load is connected to the electrical input of the radiator. The length and the amplitude of the emitted acoustic pulse were estimated using equivalent circuits of piezoelectric transducers and a spectral method based on the Fourier transforms. The optimal parameters of the electrical circuit, ensuring the minimum length of the acoustic pulses are calculated. The technique of possible measurements is described. The results are presented in the most general form, making possible to use them within different frequency ranges.

Mechanoluminescence of a Thin Composite Layer Obtained by Incorporation of SrAl2O4:(Eu2+, Dy3+) Phosphor Microparticles into a Poly(methyl methacrylate) Surface

A mechanoluminescent composite layer at the surface of poly(methyl methacrylate) (PMMA) was obtained by liquid-phase incorporation of SrAl2O4 : (Eu2+, Dy3+) phosphor microparticles into the polymer. The photoluminescence spectrum and kinetics of emission from the composite layer have been studied as dependent on the power density of exciting laser radiation pulses. The mechanoluminescence of the composite layer has been studied under the effect of short acoustic pulses and dynamic pressure of a solid stylus sliding over the composite layer surface. A possible mechanism of mechanoluminescence excitation is discussed. It is established that the obtained composite layer is characterized by high efficiency of the mechano-optical conversion and can be used for the detection and visualization of mechanical stresses.

Facial Tightening Following a Single Acoustic Wave Treatment Using Focused and Radial Acoustic Waves

Background: Acoustic wave has been used for many medical purposes, and although it is widely applied in cosmetic procedures, it has not been conducted for facial rejuvenation and tightening. Acoustic wave has been proven to penetrate deeper than subcutaneous tissue, independent of skin color, and to be beneficial for skin tightening and body contouring. Objective: To evaluate the effectiveness of a single acoustic wave treatment session using unique focused and radial acoustic waves for facial tightening. Participants: Sixty Asian patients were treated between the years 2016 and 2018. The single acoustic wave treatment session consists of focused long planar acoustic pulses thought to have an effect on cells and their metabolism resulting in an increased release of fat, and radial short acoustic pulses thought to have an effect on tissues activating blood and lymphatic flow. Patients did not undergo any form of medical aesthetic treatment during the study. Measurements: Digital photographs and three-dimensional imaging were used to evaluate the results. Results: Objective assessments with digital photographs and superimposed three-dimensional color images showed preferable facial tightening effects and marked volumetric reduction on the lower one-third of the face. These results were obtained without the edematous reactions observed in laser and radiofrequency therapies, and were sustained up to 12 months. All of the patients reported satisfaction with the results and convenience of the procedure. Complications were minor and transitory, consisting of a slight tingly sensation to the teeth during the treatment, and mild erythema resolving within 5 hours. Side effects were not observed. Conclusions: The advantages of the single acoustic wave treatment are the high potency of facial tightening effects, reduction of discomfort and side effects. Taken together, these characteristics facilitate the ability to give repeated treatments and provide an alternative or adjunct treatment for patients with improved results.

Механолюминесценция тонкого слоя композиционного материала, созданного путем внедрения микрочастиц люминофора SrAl-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=- : (Eu-=SUP=-2+-=/SUP=-, Dy-=SUP=-3+-=/SUP=-) в поверхностный слой полиметилметакрилата

AbstractA mechanoluminescent composite layer at the surface of poly(methyl methacrylate) (PMMA) was obtained by liquid-phase incorporation of SrAl_2O_4 : (Eu^2+, Dy^3+) phosphor microparticles into the polymer. The photoluminescence spectrum and kinetics of emission from the composite layer have been studied as dependent on the power density of exciting laser radiation pulses. The mechanoluminescence of the composite layer has been studied under the effect of short acoustic pulses and dynamic pressure of a solid stylus sliding over the composite layer surface. A possible mechanism of mechanoluminescence excitation is discussed. It is established that the obtained composite layer is characterized by high efficiency of the mechano-optical conversion and can be used for the detection and visualization of mechanical stresses.

Concepts and Tradeoffs in Velocity Estimation With Plane-Wave Contrast-Enhanced Doppler.

While long Doppler ensembles are, in principle, beneficial for velocity estimates, short acoustic pulses must be used in microbubble contrast-enhanced (CE) Doppler to mitigate microbubble destruction. This introduces inherent tradeoffs in velocity estimates with autocorrelators, which are studied here. A model of the autocorrelation function adapted to the microbubble Doppler signal accounting for transit time, the echo frequency uncertainty, and contrast-agent destruction is derived and validated in vitro. It is further demonstrated that a local measurement of the center frequency of the microbubble echo is essential in order to avoid significant bias in velocity estimates arising from the linear and nonlinear frequency-dependent scattering of microbubbles and compensate for the inherent speckle nature of the received echo frequency. For these reasons, broadband Doppler estimators (2-D autocorrelator and Radon projection) are better suited than simpler narrow-band estimators (1-D autocorrelator and 1-D Fourier transform) for CE flow assessment. A case study of perfusion in a VX-2 carcinoma using CE plane-wave Doppler is also shown. We demonstrate that even when considering all uncertainties associated with microbubble-related decorrelation (destruction, pulse bandwidth, transit time, and flow gradient) and the need for real-time imaging, a coefficient of variation of 4% on the axial velocity is achievable with plane-wave imaging.

The effect of acoustic shielding of the region of a dolphin's mental foramina on its hearing sensitivity

The effect of acoustic shielding of the mental foramina of a bottlenose dolphin (Tursiops truncatus) on its auditory thresholds has been experimentally studied using the method of instrumental conditioned reflexes with food reinforcement. The detection thresholds of short broadband acoustic pulses deteriorated significantly (by 30–50dB) under conditions of acoustic shielding in the region of the mental foramina over the whole frequency band of the dolphin's hearing. Therefore, the mental foramina of its lower jaw take part in receiving and conducting the sounds into the mandibular fat in the entire frequency range of the dolphin's hearing. The obtained results give an experimental proof for the assumption that the morphological structures of the lower jaw play a role of the peripheral part of a dolphin's hearing. Now there are grounds to assume that Odontoceti have the similar peripheral part of their hearing. This assumption is based on the similarity of their morphology.

Viability of endothelial cells after ultrasound-mediated sonoporation: Influence of targeting, oscillation, and displacement of microbubbles

Microbubbles (MBs) have been shown to create transient or lethal pores in cell membranes under the influence of ultrasound, known as ultrasound-mediated sonoporation. Several studies have reported enhanced drug delivery or local cell death induced by MBs that are either targeted to a specific biomarker (targeted microbubbles, tMBs) or that are not targeted (non-targeted microbubbles, ntMBs). However, both the exact mechanism and the optimal acoustic settings for sonoporation are still unknown. In this study we used real-time uptake patterns of propidium iodide, a fluorescent cell impermeable model drug, as a measure for sonoporation. Combined with high-speed optical recordings of MB displacement and ultra-high-speed recordings of MB oscillation, we aimed to identify differences in MB behavior responsible for either viable sonoporation or cell death. We compared ntMBs and tMBs with identical shell compositions exposed to long acoustic pulses (500–50,000cycles) at various pressures (150–500kPa).Propidium iodide uptake highly correlated with cell viability; when the fluorescence intensity still increased 120s after opening of the pore, this resulted in cell death. Higher acoustic pressures and longer cycles resulted in more displacing MBs and enhanced sonoporation. Non-displacing MBs were found to be the main contributor to cell death, while displacement of tMBs enhanced reversible sonoporation and preserved cell viability. Consequently, each therapeutic application requires different settings: non-displacing ntMBs or tMBs are advantageous for therapies requiring cell death, especially at 500kPa and 50,000cycles, whereas short acoustic pulses causing limited displacement should be used for drug delivery.

Crystallisation of minerals from concentrated saline dairy effluent

An understanding of crystallisation within saline effluents is important for the design of both brine crystallisers and brine disposal ponds. In this work, crystallisation of a saline effluent concentrate from the Australian dairy industry has been examined at 22 wt% and 30 wt% total solids and at temperatures between 10 and 70 °C. The precipitation occurs more rapidly at higher temperatures. This trend is dictated by precipitation of calcium phosphate salts, albeit the major constituents of the mixture are NaCl and lactose. The crystallisation induction time can be shortened by introducing cavitation induced by ultrasound. In particular, the use of two short acoustic pulses between 3.7 J/g and 16 J/g at 20 kHz spaced ten minutes apart has maximum impact upon both induction time and crystal size. It is believed that the first ultrasound pulse either generates new nuclei or enhances the mass transfer of solute toward the surface of sub-micron growing crystals. Conversely, the second pulse disrupts the growing crystals and forms secondary nuclei. The ultrasound cannot shift the solution equilibrium and so is not able to improve the low crystal yield. To increase this total yield, further evaporation is necessary. The work provides direction to personnel in the dairy industry of the feasibility of brine crystallisation with respect to energy demand and solid recovery.

Characterization of spark-generated N-waves in air using an optical schlieren method.

Accurate measurement of high-amplitude, broadband shock pulses in air is an important part of laboratory-scale experiments in atmospheric acoustics. Although various methods have been developed, specific drawbacks still exist and need to be addressed. Here, a schlieren optical method was used to reconstruct the pressure signatures of nonlinear spherically diverging short acoustic pulses generated using an electric spark source (2.5 kPa, 33 μs at 10 cm from the source) in homogeneous air. A high-speed camera was used to capture light rays deflected by refractive index inhomogeneities, caused by the acoustic wave. Pressure waveforms were reconstructed from the light intensity patterns in the recorded images using an Abel-type inversion method. Absolute pressure levels were determined by analyzing at different propagation distances the duration of the compression phase of pulses, which changed due to nonlinear propagation effects. Numerical modeling base on the generalized Burgers equation was used to evaluate the smearing of the waveform caused by finite exposure time of the high-speed camera and corresponding limitations in resolution of the schlieren technique. The proposed method allows the study of the evolution of spark-generated shock waves in air starting from the very short distances from the spark, 30 mm, up to 600 mm.