Cavitation Monitoring Research Articles

Modeling and numerical simulation of the bubble cloud dynamics in an ultrasound field for burst wave lithotripsy

Modeling and numerical simulation of bubble clouds induced by intense ultrasound waves are conducted to quantify the effect of cloud cavitation on burst wave lithotripsy, a proposed non-invasive alternative to shock wave lithotripsy that uses pulses of ultrasound with an amplitude of O(1) MPa and a frequency of O(100) kHz. A unidirectional acoustic source model and an Eulerian-Lagrangian method are developed for simulation of ultrasound generation from a multi-element array transducer and cavitation bubbles, respectively. Parametric simulations of the spherical bubble cloud dynamics reveal a new scaling parameter that dictates both the structure of the bubble cloud and the amplitude of the far-field, bubble-scattered acoustics. The simulation further shows that a thin layer of bubble clouds nucleated near a kidney stone model can shield up to 90% of the incoming wave energy, indicating a potential loss of efficacy during the treatment due to cavitation. Strong correlations are identified between the far-field, bubble-scattered acoustics and the magnitude of the shielding, which could be used for ultrasound monitoring of cavitation during treatments. The simulations are validated by companion experiments in vitro. [The work was supported by NIH P01-DK043881 and K01-DK104854.]

Broadband Ultrasonic Attenuation Estimation and Compensation With Passive Acoustic Mapping.

Several active and passive techniques have been developed to detect, localize, and quantify cavitation activity during therapeutic ultrasound procedures. Much of the prior cavitation monitoring research has been conducted using lossless in vitro systems or small animal models in which path attenuation effects were minimal. However, the performance of these techniques may be substantially degraded by attenuation between the internal therapeutic target and the external monitoring system. As a further step toward clinical application of passive acoustic mapping (PAM), this paper presents methods for attenuation estimation and compensation based on broadband cavitation data measured with a linear ultrasound array. Soft tissue phantom experiment results are used to illustrate: 1) the impact of realistic attenuation on PAM; 2) the possibility of estimating attenuation from cavitation data; 3) cavitation source energy estimation following attenuation compensation; and 4) the impact of sound speed uncertainty on PAM-related processing. Cavitation-based estimates of attenuation were within 1.5%-6.2% of the values found from conventional through-transmission measurements. Tissue phantom attenuation reduced the PAM energy estimate by an order of magnitude, but array data compensation using the cavitation-based attenuation spectrum enabled recovery of the PAM energy estimate to within 2.9%-5.9% of the values computed in the absence of the phantom. Sound speed uncertainties were found to modestly impact attenuation-compensated PAM energies, inducing errors no larger than 28% for a 40-m/s path-averaged speed error. Together, the results indicate the potential to significantly enhance the quantitative capabilities of PAM for ensuring therapeutic safety and efficacy.

Impact of stone characteristics on cavitation in burst wave lithotripsy.

Non-invasive kidney stone treatments such as shock wave lithotripsy (SWL) and burst wave lithotripsy (BWL) rely on the delivery of pressure waves through tissue to the stone. In both SWL and BWL, the potential to hinder comminution by exciting cavitation proximal to the stone has been reported. To elucidate how different stones alter prefocal cavitation in BWL, different natural and synthetic stones were treated in vitro using a therapy transducer operating at 350 kHz (peak negative pressure 7 MPa, pulse length 20 cycles, pulse repetition frequency 10 Hz). Stones were held in a confined volume of water designed to mimic the geometry of a kidney calyx, with the water filtered and degassed to maintain conditions for which the cavitation threshold (in the absence of a stone) matches that from in vivo observations. Stone targeting and cavitation monitoring were performed via ultrasound imaging using a diagnostic probe aligned coaxially with the therapy transducer. Quantitative differences in the extent and location of cavitation activity were observed for different stone types-e.g., "softer" stones (natural and synthetic) that disintegrate into "dusty" fragments produced larger prefocal cavitation clouds. Future work will focus on correlation of such cavitation metrics with stone fragmentation.

Modeling and numerical simulation of the bubble cloud dynamics in an ultrasound field for burst wave lithotripsy.

Modeling and numerical simulation of bubble clouds induced by intense ultrasound waves are conducted to quantify the effect of cloud cavitation on burst wave lithotripsy, a proposed non-invasive alternative to shock wave lithotripsy that uses pulses of ultrasound with an amplitude of O(1) MPa and a frequency of O(100) kHz. A unidirectional acoustic source model and an Eulerian-Lagrangian method are developed for simulation of ultrasound generation from a multi-element array transducer and cavitation bubbles, respectively. Parametric simulations of the spherical bubble cloud dynamics reveal a new scaling parameter that dictates both the structure of the bubble cloud and the amplitude of the far-field, bubble-scattered acoustics. The simulation further shows that a thin layer of bubble clouds nucleated near a kidney stone model can shield up to 90% of the incoming wave energy, indicating a potential loss of efficacy during the treatment due to cavitation. Strong correlations are identified between the far-field, bubble-scattered acoustics and the magnitude of the shielding, which could be used for ultrasound monitoring of cavitation during treatments. The simulations are validated by companion experiments in vitro.

Simultaneous Ultrasound Therapy and Monitoring of Microbubble-Seeded Acoustic Cavitation Using a Single-Element Transducer.

Ultrasound-driven microbubble (MB) activity is used in therapeutic applications such as blood clot dissolution and targeted drug delivery. The safety and performance of these technologies are linked to the type and distribution of MB activities produced within the targeted area, but controlling and monitoring these activities in vivo and in real time has proven to be difficult. As therapeutic pulses are often milliseconds long, MB monitoring currently requires a separate transducer used in a passive reception mode. Here, we present a simple, inexpensive, integrated setup, in which a focused single-element transducer can perform ultrasound therapy and monitoring simultaneously. MBs were made to flow through a vessel-mimicking tube, placed within the transducer's focus, and were sonicated with therapeutic pulses (peak rarefactional pressure: 75-827 kPa, pulse lengths: [Formula: see text] and 20 ms). The MB-seeded acoustic emissions were captured using the same transducer. The received signals were separated from the therapeutic signal with a hybrid coupler and a high-pass filter. We discriminated the MB-generated cavitation signal from the primary acoustic field and characterized MB behavior in real time. The simplicity and versatility of our circuit could make existing single-element therapeutic transducers also act as cavitation detectors, allowing the production of compact therapeutic systems with real time monitoring capabilities.

Gerotor pump cavitation monitoring and fault diagnosis using vibration analysis through the employment of auto-regressive-moving-average technique

Gerotor pumps, as well known, are widely used in lubrication circuits of internal combustion engines for their simplicity, high efficiency and low costs.In this paper an experimental characterization of a Gerotor pump is shown. The research is a collaboration between the Hydraulic Power Research Group (HPRG) of the University of Naples “Federico II” and the Istituto Motori of CNR.The aim of this research is to investigate the possibility of using simple data to acquire, as vibrational data, on the pump under investigation to detect possible cavitation problem by implementing a proper mathematical procedure to this aim. As been demonstrated that these pumps are particularly subject to cavitation.The gerotor pumps are much subject to cavitate than expected, especially under particular operating conditions of the engine. Cavitation is also correlate to vehicle dynamics particularly with the recent tendency to reduce the mass of oil in the sump. Therefore, the research to avoid cavitation is crucial nowadays. Consequently this study has been firstly performed with an experimentation on the pump by monitoring the delivered oil flow-rate and the adsorbed torque on the pump shaft. An accurate analysis of the pressure oscillations in cavitation conditions, has been, also, conducted. Then, an accelerometer sensor has been properly located to study the cavitation with a fault diagnosis system based on vibration detection.The experimental tests have been performed on a test bench of the Hydraulic Laboratory of the University of Naples “Federico II” in Italy. The bench allows testing the pump working by varying the shaft speed, the oil temperature, the suction and the delivery pressure. The main measured parameters are shaft torque, oil flow rate, mean suction and delivery pressure and the instantaneous suction and delivery pressure.As expected, tests revealed the high influence of the suction pressure on the delivered oil flow rate, while no significant influence has been noted on the adsorbed torque. Furthermore, the pressure oscillations in the pump delivery are highly influenced by the suction pressure.A non intrusive accelerometer has been installed during the experimentation on the oil pump. Since the vibration due to cavitation is the main concern of this study, the accelerometer has been mounted at the suction port in the radial direction.More precisely, the paper presents a fault diagnosis system based on vibration detection. Firstly, a Fast Fourier Transform of the vibration signal has been computed. The investigation has been made with and without the presence of cavitation varying the pump rotation speeds. Limitations due to the detecting of the on line cavitation problems by monitoring the FFT vibration spectra have been overcame by implementing an alternative method based on stochastic approach.This diagnosis method of accelerometer time series analysis based on an Auto Regressive and Moving Average (ARMA) method has been used to determine the pump failure. The diagnosis results have demonstrated the ability of the proposed mathematical technique in the identification of cavitation phenomena proving that the proposed approach is a useful methodology to detect the presence of fault. The approach can predict, with good accuracy, pump failure in real time operation. In addition, a threshold vibration level in decibel scale is also fixed.

Characterizing Focused-Ultrasound Mediated Drug Delivery to the Heterogeneous Primate Brain In Vivo with Acoustic Monitoring.

Focused ultrasound with microbubbles has been used to noninvasively and selectively deliver pharmacological agents across the blood-brain barrier (BBB) for treating brain diseases. Acoustic cavitation monitoring could serve as an on-line tool to assess and control the treatment. While it demonstrated a strong correlation in small animals, its translation to primates remains in question due to the anatomically different and highly heterogeneous brain structures with gray and white matteras well as dense vasculature. In addition, the drug delivery efficiency and the BBB opening volume have never been shown to be predictable through cavitation monitoring in primates. This study aimed at determining how cavitation activity is correlated with the amount and concentration of gadolinium delivered through the BBB and its associated delivery efficiency as well as the BBB opening volume in non-human primates. Another important finding entails the effect of heterogeneous brain anatomy and vasculature of a primate brain, i.e., presence of large cerebral vessels, gray and white matter that will also affect the cavitation activity associated with variation of BBB opening in different tissue types, which is not typically observed in small animals. Both these new findings are critical in the primate brain and provide essential information for clinical applications.

A multi-frequency sparse hemispherical ultrasound phased array for microbubble-mediated transcranial therapy and simultaneous cavitation mapping

Focused ultrasound (FUS) phased arrays show promise for non-invasive brain therapy. However, the majority of them are limited to a single transmit/receive frequency and therefore lack the versatility to expose and monitor the treatment volume. Multi-frequency arrays could offer variable transmit focal sizes under a fixed aperture, and detect different spectral content on receive for imaging purposes. Here, a three-frequency (306, 612, and 1224 kHz) sparse hemispherical ultrasound phased array (31.8 cm aperture; 128 transducer modules) was constructed and evaluated for microbubble-mediated transcranial therapy and simultaneous cavitation mapping. The array is able to perform effective electronic beam steering over a volume spanning (−40, 40) and (−30, 50) mm in the lateral and axial directions, respectively. The focal size at the geometric center is approximately 0.9 (2.1) mm, 1.7 (3.9) mm, and 3.1 (6.5) mm in lateral (axial) pressure full width at half maximum (FWHM) at 1224, 612, and 306 kHz, respectively. The array was also found capable of dual-frequency excitation and simultaneous multi-foci sonication, which enables the future exploration of more complex exposure strategies. Passive acoustic mapping of dilute microbubble clouds demonstrated that the point spread function of the receive array has a lateral (axial) intensity FWHM between 0.8–3.5 mm (1.7–11.7 mm) over a volume spanning (−25, 25) mm in both the lateral and axial directions, depending on the transmit/receive frequency combination and the imaging location. The device enabled both half and second harmonic imaging through the intact skull, which may be useful for improving the contrast-to-tissue ratio or imaging resolution, respectively. Preliminary in vivo experiments demonstrated the system’s ability to induce blood–brain barrier opening and simultaneously spatially map microbubble cavitation activity in a rat model. This work presents a tool to investigate optimal strategies for non-thermal FUS brain therapy and concurrent microbubble cavitation monitoring through the availability of multiple frequencies.

Performance investigation of reciprocating pump running with organic fluid for organic Rankine cycle

Organic Rankine cycles (ORC) are used to convert lowgrade heat sources into power. Current research and development investigate small scale and variable heat sources application such as waste heat recovery. Many experimental data on ORC are available. Feed-pump performances achieved are lower than expected and some authors reported cavitation issue. Pump performance has a non-negligible impact over the ORC performance, especially for transcritical cycles. Operations of diaphragm pumps in three different test benches with different fluid and pump size are analyzed. A semi-empirical model of the pump power chain is proposed and validated. Energetic analysis show highlevel of losses in the variable speed drive and electric motor, mainly due to design oversizing. Then a model and analysis of reciprocating pump volumetric efficiency is proposed, taking into account fluid properties. Finally, cavitation limits in different conditions are calculated. Required Net Positive Suction Head (NPSHr) calculated for R134a are found to be in accordance with manufacturer limits for water. Pump vibration sensor could be used for cavitation monitoring. This work gives information for ORC feed-pump simulation, design and operation.

Locally-concentrated sonicated microbubbles: Potential as an antibiotic

While the antimicrobial effects of ultrasound have been well established, application as a bactericide in medicine has been hindered in part by significant variation in reported efficacy. Non-thermal mechanisms of cell death are generally attributed to cavitation, prompting us to investigate the potential for locally applied microbubbles to serve as a catalyst for reliably increasing bacterial death, while sparing surrounding cells. This preliminary study was limited to gram-negative bacteria (E-coli) suspended in buffered saline. Preliminary work at 40 kHz continuous-wave sonication established a threshold time for our setup of 15 minutes, below which negligible cell death was observed relative to control samples. Experiments were then performed with and without the introduction of octofluropropane-filled lipid shells microbubbles, sonicated over the 15 minute period. Thermometry and passive cavitation monitoring (PCD) were both conducted. Analysis by dilution and plating indicate a 65-80% reduction in b...

Deconvolution of acoustically detected bubble-collapse shock waves

The shock wave emitted by the collapse of a laser-induced bubble is detected at propagation distances of 30, 40and50mm, using a PVdF needle hydrophone, with a non-flat end-of-cable frequency response, calibrated for magnitude and phase, from 125kHz to 20MHz. High-speed shadowgraphic imaging at 5×106 frames per second, 10nstemporal resolution and 256 frames per sequence, records the bubble deflation from maximum to minimum radius, the collapse and shock wave generation, and the subsequent rebound in unprecedented detail, for a single sequence of an individual bubble. The Gilmore equation for bubble oscillation is solved according to the resolved bubble collapse, and simulated shock wave profiles deduced from the acoustic emissions, for comparison to the hydrophone recordings. The effects of single-frequency calibration, magnitude-only and full waveform deconvolution of the experimental data are presented, in both time and frequency domains. Magnitude-only deconvolution increases the peak pressure amplitude of the measured shock wave by approximately 9%, from single-frequency calibration, with full waveform deconvolution increasing it by a further 3%. Full waveform deconvolution generates a shock wave profile that is in agreement with the simulated profile, filtered according to the calibration bandwidth. Implications for the detection and monitoring of acoustic cavitation, where the role of periodic bubble collapse shock waves has recently been realised, are discussed.

Wavelet-transform-based active imaging of cavitation bubbles in tissues induced by high intensity focused ultrasound.

Cavitation detection and imaging are essential for monitoring high-intensity focused ultrasound (HIFU) therapies. In this paper, an active cavitation imaging method based on wavelet transform is proposed to enhance the contrast between the cavitation bubbles and surrounding tissues. The Yang-Church model, which is a combination of the Keller-Miksis equation with the Kelvin-Voigt equation for the pulsations of gas bubbles in simple linear viscoelastic solids, is utilized to construct the bubble wavelet. Experiments with porcine muscles demonstrate that image quality is associated with the initial radius of the bubble wavelet and the scale. Moreover, the Yang-Church model achieves a somewhat better performance compared with the Rayleigh-Plesset-Noltingk-Neppiras-Poritsky model. Furthermore, the pulse inversion (PI) technique is combined with bubble wavelet transform to achieve further improvement. The cavitation-to-tissue ratio (CTR) of the best tissue bubble wavelet transform (TBWT) mode image is improved by 5.1 dB compared with that of the B-mode image, while the CTR of the best PI-based TBWT mode image is improved by 7.9 dB compared with that of the PI-based B-mode image. This work will be useful for better monitoring of cavitation in HIFU-induced therapies.

Neuroprotection and neurorestoration through the opened blood-brain barrier using focused ultrasound and microbubbles

After cancer and heart disease, neurodegenerative diseases, such as Alzheimer's, Parkinson's, multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS), take more lives each year than any other illness. Although some effective treatments are available, most of those diseases remain undertreated. The blood-brain barrier (BBB) has been proclaimed as the “bottleneck“ of brain drug delivery. Focused ultrasound (FUS) in conjunction with microbubbles is currently the only technique that can open the BBB locally, transiently, and noninvasively. Our group has demonstrated that pharmacological compounds of variable sizes can not only traverse the BBB but also induce therapeutic effects in the presence of neurodegenerative disease. In this paper, the trans-BBB neurotherapeutic delivery with FUS is shown to (1) be safely facilitated within a specific pressure range in both mice and non-human primates through the mechanism of cavitation, (2) be controlled through the pressure amplitude and microbubble characteristics, (3) induce downstream signaling effects in the neuronal cell, (4) trigger neuroprotection and neurorestoration relevant in the treatment of neurodegeneration, (5) be localized and monitored in real time through cavitation monitoring and mapping. BBB opening is combined with systemic administration of neurotrophic molecules or adeno-associated viruses that allow for neuronal protection and growth in the BBB-opened regions.

Cavitation Aggressiveness Estimation in Hydro Turbines Based on Cyclostationary Modeling

This work proposes a new methodology of detection and identification of erosive cavitation in hydro turbines, which is based on cyclostationary modeling of the cavitation induced vibrational signals. Different cavitation types cause damage to different turbine parts and induce different vibrational signatures, which can be employed to identify and locate the cavitation. Additionally, the cavitation aggressiveness can be estimated using the measured power of vibrational signal. High frequency accelerometers picked up the signals from two real turbines under normal operation. The methodology was implemented in software and a specific hardware was developed to run the software locally. Signals were synthesized in accord with the cyclostationary modeling and employed to validate the proposed methodology. Results obtained from real signals were similar to the ones obtained from synthetic signals, and corroborate the feasibility of this methodology in cavitation monitoring systems.

In Vitro Investigation of the Individual Contributions of Ultrasound-Induced Stable and Inertial Cavitation in Targeted Drug Delivery

Ultrasound-mediated targeted drug delivery is a therapeutic modality under development with the potential to treat cancer. Its ability to produce local hyperthermia and cell poration through cavitation non-invasively makes it a candidate to trigger drug delivery. Hyperthermia offers greater potential for control, particularly with magnetic resonance imaging temperature measurement. However, cavitation may offer reduced treatment times, with real-time measurement of ultrasonic spectra indicating drug dose and treatment success. Here, a clinical magnetic resonance imaging-guided focused ultrasound surgery system was used to study ultrasound-mediated targeted drug delivery in vitro. Drug uptake into breast cancer cells in the vicinity of ultrasound contrast agent was correlated with occurrence and quantity of stable and inertial cavitation, classified according to subharmonic spectra. During stable cavitation, intracellular drug uptake increased by a factor up to 3.2 compared with the control. Reported here are the value of cavitation monitoring with a clinical system and its subsequent employment for dose optimization.

Cavitation erosion of the calcium carbonate deposits

The paper presents the research of erosion effects caused by acoustic cavitation on metallic and enamelled specimens coated with calcium carbonate - scale. The deposition of calcium carbonate was performed under controlled laboratory conditions. The deposition took place at the same integral conditions to the specimens of different surface roughness. Cavitation as a cause of erosion was generated in a vessel with ultrasonic excitation. Simultaneously with the monitoring of cavitation above the specimens, the destruction of scale on the surface of specimens was analysed. The results of experiments indicate a characteristic effect of cavitation intensity on the destruction of scale surface layer. The intensity of cavitation erosion is proportional to the voltage on the sonotrode or the intensity of pressure fluctuations, and depends on the roughness of the surface of specimens, on which the scales were deposited.

Image-guided sonothrombolysis in a stroke model with a cavitation delivery and monitoring system

Microbubbles (MB) and ultrasound (US) can dissolve intra-arterial thrombi. In order to reproducibly deliver the correct cavitation dose and ensure treatment efficacy and safety, we designed a therapeutic US mode with cavitation monitoring. Therapy delivery and recording of the MB signal are achieved with a sector imaging probe. Monitoring is achieved by spectrally analyzing the MB signal: ultraharmonics are a marker of stable cavitation (SC) and broadband noise characterizes inertial cavitation (IC). We used the system in a pig model. Thrombotic occlusions were created by injecting 4-hour old clots bilaterally into the internal carotids. Forty pigs were randomized to either 2.4 MI, 5 μs pulses with MBs; 1.7 MI, 20 μs pulses with MBs; and 2.4 MI, 5 μs pulses without MBs. Angiographic recanalization rates were compared. Cavitation as a function of MI was estimated in vivo. Dominant SC started at an applied MI of 0.6 (0.3MI in situ after derating by skull attenuation). Dominant IC was estimated to start at an applied MI of 0.9 (0.6 in situ). Thus, all therapy settings were in the IC regime. The 2.4MI + MB setting was the most effective (100% recanalization) vs 38% for the 1.7MI + MB and 50% for 2.4 MI without MBs (both p<0.05 compared to 2.4MI + MB). No signs of hemorrhage were found in any animal. In conclusion, higher IC levels are most effective for thrombus dissolution. Spectral analysis techniques can be used to plan and monitor the therapy.

Instigation and monitoring of inertial cavitation from nanoscale particles using a diagnostic imaging platform and passive acoustic mapping

Inertial cavitation nucleated by microbubble contrast agents has been recently shown to enhance extravasation and improve the distribution of anti-cancer agents during ultrasound (US)-enhanced delivery. However, microbubbles require frequent replenishment due to their rapid clearance and destruction upon US exposure and are unable to extravasate into tumor tissue due to their large size. A new generation of gas-stabilizing polymeric cup-shaped nanoparticles, or “nanocups” (NCs), have been formulated to a size that enables exploitation of the enhanced permeability and retention effect for intratumoral accumulation. NCs provide sustained inertial cavitation, as characterized by broadband emissions, at peak rarefactional pressures readily achievable by diagnostic ultrasound systems. This enables the use of a single low-cost system for B-mode treatment guidance, instigation of cavitation, and real-time passive acoustic mapping (PAM) of the location and extent of cavitation activity during therapy. The significant lowering of the inertial cavitation threshold in the presence of NCs as characterized by PAM is first quantified in-vitro. In-vivo and ex-vivo results in xenograft-implanted tumor bearing mice further evidence the strong presence of inertial cavitation detectable in the tumor at diagnostic levels of US intensity, as confirmed by PAM images overlaid on B-mode in real-time.

Drug delivery through the opened blood-brain barrier in mice and non-human primates

Over five million U.S. men and women suffer from neurodegenerative diseases. Although great progress has been made in recent years toward understanding of these diseases, few effective treatments and no cures are currently available. This is mainly due to the impermeability of the blood-brain barrier (BBB) that allows only 5% of more than 7000 small-molecule drugs available to treat only a tiny fraction of these diseases. Safe and localized opening of the BBB has been proven to present a significant challenge. Focused ultrasound (FUS), in conjunction with microbubbles, remains the sole technique that can induce localized BBB opening noninvasively and regionally. In the past, our group has focused on cavitation monitoring during BBB opening in both mice and non-human primates, assessment of safety and drug efficacy using behavioral testing, delivery of molecules of variant size through the opened BBB, investigation on the role of the microbubble diameter and use of nanodroplets. We will briefly highlight these past findings as well as introduce newer accomplishments such as its role in enhancement of drugs for neuroprotection and neuroregeneration in the treatment of Parkinson's, the use of alternative routes of systemic administration for larger drug dosage, dependence of the BBB opening size on the acoustic pressure, real-time monitoring of the microbubble perfusion of the brain, cavitation prediction of the timeline of BBB opening, and targeted delivery using adeno-associated viruses.

Portable high-intensity focused ultrasound system with 3D electronic steering, real-time cavitation monitoring, and 3D image reconstruction algorithms: a preclinical study in pigs.

Purpose:The aim of this study was to evaluate the safety and accuracy of a new portable ultrasonography-guided high-intensity focused ultrasound (USg-HIFU) system with a 3-dimensional (3D) electronic steering transducer, a simultaneous ablation and imaging module, real-time cavitation monitoring, and 3D image reconstruction algorithms.Methods:To address the accuracy of the transducer, hydrophones in a water chamber were used to assess the generation of sonic fields. An animal study was also performed in five pigs by ablating in vivo thighs by single-point sonication (n=10) or volume sonication (n=10) and ex vivo kidneys by single-point sonication (n=10). Histological and statistical analyses were performed.Results:In the hydrophone study, peak voltages were detected within 1.0 mm from the targets on the y- and z-axes and within 2.0-mm intervals along the x-axis (z-axis, direction of ultrasound propagation; y- and x-axes, perpendicular to the direction of ultrasound propagation). Twenty-nine of 30 HIFU sessions successfully created ablations at the target. The in vivo porcine thigh study showed only a small discrepancy (width, 0.5-1.1 mm; length, 3.0 mm) between the planning ultrasonograms and the pathological specimens. Inordinate thermal damage was not observed in the adjacent tissues or sonic pathways in the in vivo thigh and ex vivo kidney studies.Conclusion:Our study suggests that this new USg-HIFU system may be a safe and accurate technique for ablating soft tissues and encapsulated organs.