Ultrasound Frequency Research Articles

Optimizing irradiation conditions for low-intensity pulsed ultrasound to upregulate endothelial nitric oxide synthase.

Here we aimed to develop a minimally invasive treatment for ischemic heart disease and demonstrate that low-intensity pulsed ultrasound (LIPUS) therapy improves myocardial ischemia by promoting myocardial angiogenesis in a porcine model of chronic myocardial ischemia. Studies to date determined the optimal treatment conditions within the range of settings available with existing ultrasound equipment and did not investigate a wider range of conditions. We investigated a broad range of five parameters associated with ultrasound irradiation conditions that promote expression of endothelial nitric oxide synthase (eNOS), a key molecule that promotes angiogenesis in human coronary artery endothelial cells (HCAEC). Suboptimal irradiation conditions included 1-MHz ultrasound frequency, 500-kPa sound pressure, 20-min total irradiation time, 32-48-[Formula: see text] pulse duration, and 320-[Formula: see text] pulse repetition time. Furthermore, a proposed index, [Formula: see text], calculated as the product of power and the total number of irradiation cycles applied to cells using LIPUS, uniformly revealed the experimental eNOS expression associated with the various values of five parameters under different irradiation conditions. We determined the suboptimal ultrasound irradiation conditions for promoting eNOS expression in HCAEC.

Rapid intraoperative multi-molecular diagnosis of glioma with ultrasound radio frequency signals and deep learning

Molecular diagnosis is crucial for biomarker-assisted glioma resection and management. However, some limitations of current molecular diagnostic techniques prevent their widespread use intraoperatively. With the unique advantages of ultrasound, this study developed a rapid intraoperative molecular diagnostic method based on ultrasound radio-frequency signals. We built a brain tumor ultrasound bank with 169 cases enrolled since July 2020, of which 43483 RF signal patches from 67 cases with a pathological diagnosis of glioma were a retrospective cohort for model training and validation. IDH1 and TERT promoter (TERTp) mutations and 1p/19q co-deletion were detected by next-generation sequencing. We designed a spatial-temporal integration model (STIM) to diagnose the three molecular biomarkers, thus establishing a rapid intraoperative molecular diagnostic system for glioma, and further analysed its consistency with the fifth edition of the WHO Classification of Tumors of the Central Nervous System (WHO CNS5). We tested STIM in 16-case prospective cohorts, which contained a total of 10384 RF signal patches. Two other RF-based classical models were used for comparison. Further, we included 20 cases additional prospective data for robustness test (ClinicalTrials.govNCT05656053). In the retrospective cohort, STIM achieved a mean accuracy and AUC of 0.9190 and 0.9650 (95% CI, 0.94-0.99) respectively for the three molecular biomarkers, with a total time of 3s and a 96% match to WHO CNS5. In the prospective cohort, the diagnostic accuracy of STIM is 0.85±0.04 (mean±SD) for IDH1, 0.84±0.05 for TERTp, and 0.88±0.04 for 1p/19q. The AUC is 0.89±0.02 (95% CI, 0.84-0.94) for IDH1, 0.80±0.04 (95% CI, 0.71-0.89) for TERTp, and 0.85±0.06 (95% CI, 0.73-0.98) for 1p/19q. Compared to the second best available method based on RF signal, the diagnostic accuracy of STIM is improved by 16.70% and the AUC is improved by 19.23% on average. STIM is a rapid, cost-effective, and easy-to-manipulate AI method to perform real-time intraoperative molecular diagnosis. In the future, it may help neurosurgeons designate personalized surgical plans and predict survival outcomes. A full list of funding bodies that contributed to this study can be found in the Acknowledgements section.

Hermite-scan imaging for differentiating glioblastoma from normal brain: Simulations and ex vivo studies for applications in intra-operative tumor identificationa).

Hermite-scan (H-scan) imaging is a tissue characterization technique based on the analysis of raw ultrasound radio frequency (RF) echoes. It matches the RF echoes to Gaussian-weighted Hermite polynomials of various orders to extract information related to scatterer diameter. It provides a color map of large and small scatterers in the red and blue H-scan image channels, respectively. H-scan has been previously reported for characterizing breast, pancreatic, and thyroid tumors. The present work evaluated H-scan imaging to differentiate glioblastoma tumors from normal brain tissue ex vivo. First, we conducted 2-D numerical simulations using the k-wave toolbox to assess the performance of parameters derived from H-scan images of acoustic scatterers (15-150 μm diameters) and concentrations (0.2%-1% w/v). We found that the parameter intensity-weighted percentage of red (IWPR) was sensitive to changes in scatterer diameters independent of concentration. Next, we assessed the feasibility of using the IWPR parameter for differentiating glioblastoma and normal brain tissues (n = 11 samples per group). The IWPR parameter estimates for normal tissue (44.1% ± 1.4%) were significantly different (p < 0.0001) from those for glioblastoma (36.2% ± 0.65%). These findings advance the development of H-scan imaging for potential use in differentiating glioblastoma tumors from normal brain tissue during resection surgery.

A note on the audio sound power generated by a parametric array loudspeaker.

Understanding the sound power characteristics of parametric array loudspeakers (PALs) poses a unique challenge due to the nonlinear process involved. This work addresses this issue by employing the spherical convolution directivity model to obtain the far field intensity, which is then used to calculate the sound power radiated by a PAL. The results reveal that the audio sound power is approximately proportional to the square of the audio frequency and the aperture size, while inversely proportional to the ultrasound frequency. Additionally, the conversion efficiency from ultrasound to audio sound is found to be generally below 0.15% for typical configurations.

Development and optimisation of in vitro sonodynamic therapy for glioblastoma

Sonodynamic therapy (SDT) is currently on critical path for glioblastoma therapeutics. SDT is a non-invasive approach utilising focused ultrasound to activate photosensitisers like 5-ALA to impede tumour growth. Unfortunately, the molecular mechanisms underlying the therapeutic functions of SDT remain enigmatic. This is primarily due to the lack of intricately optimised instrumentation capable of modulating SDT delivery to glioma cells in vitro. Consequently, very little information is available on the effects of SDT on glioma stem cells which are key drivers of gliomagenesis and recurrence. To address this, the current study has developed and validated an automated in vitro SDT system to allow the application and mapping of focused ultrasound fields under varied exposure conditions and setup configurations. The study optimizes ultrasound frequency, intensity, plate base material, thermal effect, and the integration of live cells. Indeed, in the presence of 5-ALA, focused ultrasound induces apoptotic cell death in primary patient-derived glioma cells with concurrent upregulation of intracellular reactive oxygen species. Intriguingly, primary glioma stem neurospheres also exhibit remarkably reduced 3D growth upon SDT exposure. Taken together, the study reports an in vitro system for SDT applications on tissue culture-based disease models to potentially benchmark the novel approach to the current standard-of-care.

Results of a hemodialysis vascular access routine ultrasound surveillance protocol and frequency of surveillance guided pre-emptive access maintenance interventions

Background: To evaluate the implementation of routine surveillance using ultrasound on hemodialysis vascular access (VA) outcomes and determine the number and frequency of corrective, surveillance-guided procedures performed. Methods: Multicenter, prospective, observational study that includes consecutive hemodialysis patients receiving therapy from native arteriovenous fistulae (AVF) or grafts (AVG). Participants were assigned to a routine VA Color Doppler ultrasound surveillance (DUS) protocol from January 2019 to December 2021. Patients were referred for corrective procedures (endovascular or surgical) based on clinical or DUS findings (pre-emptive procedures; PEP). Primary endpoint was the estimation of primary unassisted (PUP) and secondary patency (SP) rates. Secondary endpoints were the determination of the number and frequency of PEP and VA survival rates. Results: In total, 223 patients with 243 VA (192 AVF and 51 AVG) were included. Access PUP and SP rates were 83% and 93% at 12 months, 75% and 88% at 24 months, and 72% and 83% at 36 months follow-up. Autologous fistulae PUP and SP were 89% and 96% at 12 months, 81% and 93% at 24 months, and 80% and 89% at 36 months, respectively. Graft PUP and SP were 56% and 80% at 12 months, 44% and 65% at 24 months, and 39% and 54% at 36 months, respectively. In total, 56 corrective procedures (38/56 PEP; 65.5%) were performed (0.13 procedures/year), of which 34 were in AVF patients (0.09 procedures/year) and 22 in AVG patients (0.40 procedures/year). Overall, 33 VA losses occurred (0.06 failures/year), 17 in AVF (0.04 failures/year), and 16 in AVG patients (0.20 failures/year). Conclusion: The use of DUS resulted in the timely diagnosis of dysfunction, satisfactory overall VA survival, and patency rates, with a low PEP frequency. Randomized controlled trials are required to establish the value of DUS surveillance on access patency and whether DUS-guided interventions could improve VA outcomes.

Multimodal image feature fusion for improving medical ultrasound image segmentation

Ultrasound imaging is the most commonly used technique to detect abnormalities of the thyroid and diagnose abnormal breasts. However, due to the inherent characteristics of ultrasound imaging, the contrast of ultrasound images is relatively low, and the tissue boundaries in the image are blurry. This makes it a challenging task to segment thyroid or breast lesions from ultrasound images. In this work, we explore the role of multimodal features at different levels of deep neural network models and their fusion mechanisms for multimodal images generated by ultrasound radio frequency (RF) data. The ultrasound RF data contain information related to the arrangement of scatterers in tissues and organs, which is only partially available in B-mode images. To solve this problem, we use ultrasound RF data to generate parametric images, including Nakagami and entropy images, to illustrate the abundant backscattered statistics contained in RF data. A channel-aware fusion module is proposed to adaptively fuse the features from images of different modalities. Experimental results show that the abundant information contained in RF data can be helpful to identify thyroid glands or breast lesions with low contrast and fuzzy boundaries in B-mode ultrasound images and improve the segmentation performance.

Frequency dependence of ultrasonic effects on the kinetics of hen egg white lysozyme fibrillation

Our study aimed to investigate the effects of ultrasound on the fibrillation kinetics of HEWL (hen egg white lysozyme) and its physicochemical properties. Ultrasound, a mechanical wave, can induce conformational changes in proteins. To achieve this, we developed an ultrasound exposure system and used various biophysical techniques, including ThT fluorescence spectroscopy, ATR-FTIR, Far-UV CD spectrophotometry, Fluorescence microscopy, UV-spectroscopy, and seeding experiments. Our results revealed that higher frequencies significantly accelerated the fibrillation of lysozyme by unfolding the native protein and promoting the fibrillation process, thereby reducing the lag time. We observed a change in the secondary structure of the sonicated protein change to the β-structure, but there was no difference in the Tm of native and sonicated proteins. Furthermore, we found that higher ultrasound frequencies had a greater seeding effect. We propose that the effect of frequency can be explained by the impact of the Reynolds number, and for the Megahertz frequency range, we are almost at the transition regime of turbulence. Our results suggest that laminar flows may not induce any significant change in the fibrillation kinetics, while turbulent flows may affect the process.

Value of contrast-enhanced percutaneous ultrasound in the diagnosis of rotator cuff tear subtype

To explore characteristics of contrast-enhanced ultrasound (CEUS) images features and diagnostic value of rotator cuff tear subtypes. From January 2019 to March 2022, percutaneous ultrasound-guided subacromial bursography (PUSB) with persutaneous ultrasound-guide tendon lesionography (PUTL) was performed on 114 patients with suspected rotator cuff injury were evaluated, including 54 males and 60 females ranged in age from 35 to 75 years old with an average of (58.8±8.7 ) years old;76 patients on the right side and 38 patients on the left side;the course of disease ranged from 0.13 to 111 months with an average of (10.2±9.8) months. GE LOGIQ E9 color doppler ultrasound diagnostic high frequency(6 to 12 MHz) was used to CEUS Using arthroscopy as gold standard, receiver operating characteristic (ROC) curve was used to evaluate diagnostic efficacy of US, MRI and CEUS for rotator cuff injury, also sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated. The sensitivity of US in diagnosing full-thickness tears was 72.1%, specificity was 93.0%, and accuracy was 85.1%. The sensitivity, specificity and accuracy of MRI diagnosis of full-thickness tear were 90.9%, 92.6% and 92.1% respectively. The sensitivity, specificity and accuracy of CEUS in diagnosis of full-thickness tear were 100%. The sensitivity, specificity and accuracy of US in the diagnosis of partial tear were 85.7%, 77.2% and 79.8% respectively. The sensitivity, specificity and accuracy of MRI diagnosis of partial tear were 83.7%, 81.7% and 82.5% respectively. The sensitivity, specificity and accuracy of CEUS in diagnosis of partial tear were 95.7%, 92.6% and 93.9% respectively. There were significant differences in diagnosis results of US, MRI and CEUS for rotator cuff bursa tear (P<0.001). Kapp test showed good consistency between CEUS and arthroscopy in diagnosing rotator cuff tear subtypes (full-thickness and partial tears). Using PUSB/PUTL to observe distribution of contrast media in bursa, tendon and joint cavity to evaluate the type of rotator cuff tear, its diagnostic performance is significantly better than US and MRI. Therefore, percutaneous contrast-enhanced ultrasound can be a reliable method for diagnosing subtypes of rotator cuff tears.

Polymer Mechanochemistry in Microbubbles.

Polymer mechanochemistry is a promising technology to convert mechanical energy into chemical functionality by breaking covalent and supramolecular bonds site-selectively. Yet, the mechanochemical reaction rates of covalent bonds in typically used ultrasonication setups lead to reasonable conversions only after comparably long sonication times. This can be accelerated by either increasing the reactivity of the mechanoresponsive moiety or by modifying the encompassing polymer topology. Here, a microbubble system with a tailored polymer shell consisting of an N2 gas core and a mechanoresponsive disulfide-containing polymer network is presented. It is found that the mechanochemical activation of the disulfides is greatly accelerated using these microbubbles compared to commensurate solid core particles or capsules filled with liquid. Aided by computational simulations, it is found that low shell thickness, low shell stiffness and crosslink density, and a size-dependent eigenfrequency close to the used ultrasound frequency maximize the mechanochemical yield over the course of the sonication process.

Desynchronization of neuronal firing in multiparameter ultrasound stimulation

Low-intensity transcranial ultrasound stimulation, a novel neuromodulation technique, that possesses the advantages of non-invasiveness, high penetration depth, and high spatial resolution, has achieved positive neuromodulation effects in animal studies. But the regulatory mechanism remains controversial. The intramembrane cavitation effect is considered one of the mechanisms for ultrasound neuromodulation. In this study, the modified equations of ultrasonic cavitation bubble dynamics were coupled with the dual-coupled neuron Hindmarsh-Rose model, small-world neural network model, and the Jansen-Rit neural mass model, which simulate simple coupled neurons, complex neuronal networks, and discharge signals in epileptic disorders respectively. The results demonstrated that ultrasound stimulation has an appreciable modulatory effect on neuronal firing desynchronization in Hindmarsh-Rose model and small-world neural network model. The desynchronization effect is related to the stimulation frequency and intensity. Furthermore, ultrasound stimulation has an inhibitory effect on epileptic seizures, and the effect is enhanced by increasing ultrasound frequency from 0.1–1.0 MHz. This is the first combination of ultrasonic intramembrane cavitation effect theory with neurons and neural network firing desynchronization, which can provide guidance of parametric and theories support for the studies of neurological diseases such as epilepsy and Parkinson’s disease.

Contrast Agent-Free 3D Renal Ultrafast Doppler Imaging Reveals Vascular Dysfunction in Acute and Diabetic Kidney Diseases.

To combat the irreversible decline in renal function associated with kidney disease, it is essential to establish non-invasive biomarkers for assessing renal microcirculation. However, the limited resolution and/or vascular sensitivity of existing diagnostic imaging techniques hinders the visualization of complex cortical vessels. Here, a 3D renal ultrafast Doppler (UFD) imaging system that uses a high ultrasound frequency (18MHz) and ultrahigh frame rate (1KHz per slice) to scan the entire volume of a rat's kidney in vivo is demonstrated. The system, which can visualize the full 3D renal vascular branching pyramid at a resolution of 167µm without any contrast agent, is used to chronically and noninvasively monitor kidneys with acute kidney injury (AKI, 3 days) and diabetic kidney disease (DKD, 8 weeks). Multiparametric UFD analyses (e.g., vessel volume occupancy (VVO), fractional moving blood volume (FMBV), vessel number density (VND), and vessel tortuosity (VT)) describe rapid vascular rarefaction from AKI and long-term vascular degeneration from DKD, while the renal pathogeneses are validated by in vitro blood serum testing and stained histopathology. This work demonstrates the potential of 3D renal UFD to offer valuable insights into assessing kidney perfusion levels for future research in diabetes and kidney transplantation.

A level-set method for ultrasound-driven bubble motion and tissue deformation

Ultrasound-driven bubble collapse and resulting tissue deformation are numerically investigated by combining a level-set method for determining the liquid–gas and liquid–solid interfaces and a full Eulerian method to solve the unified governing equations for both solid and fluid phases. The fluid compressibility effect is considered by employing the van der waals and Tait equations of state for gas and liquid, respectively, and a semi-implicit pressure correction method is used to effectively capture ultrasound and shock waves. Two tissue models, treating tissue as a viscoelastic solid or as a fluid with large surface tension, are compared in terms of the bubble expansion and compression processes and tissue deformation patterns. Computations are also carried out to investigate the influences of ultrasonic pulse amplitude, ultrasound frequency, and bubble-tissue distance on the bubble-tissue interaction.

Increased intracellular diffusivity of macromolecules within a mammalian cell by low-intensity pulsed ultrasound

Whilst a number of studies have demonstrated that low-intensity pulsed ultrasound (LIPUS) is a promising therapeutic ultrasound technique that can be used for delivering mild mechanical stimuli to target tissue non-invasively, the underlying biophysical mechanisms still remain unclear. Most mechanism studies have focused explicitly on the effects of LIPUS on the cell membrane and mechanosensitive receptors. In the present study, we propose an additional mechanism by which LIPUS propagation through living cells may directly impact intracellular dynamics, particularly the diffusion transport of biomolecules. To support our hypothesis, human epithelial-like cells (SaOS-2 and HeLa) seeded on a confocal dish placed on a microscope stage were exposed to LIPUS with various exposure conditions (ultrasound frequencies of 0.5, 1 and 3 MHz, peak acoustic pressure of 200 and 400 kPa, a pulse repetition frequency of 1 kHz and a 20 % duty cycle), and the diffusivities of various sizes of biomolecules in the cytoplasm area were measured using fluorescence recovery after photobleaching (FRAP). Furthermore, giant unilamellar vesicles (GUVs) filled with macromolecules were used to examine the physical causal relationship between LIPUS and molecular diffusion changes. Nucleocytoplasmic transport coefficients were also measured by modified FRAP that bleaches the whole cell nuclear region. Extracellular signal-regulated kinases (ERK) activity (the phosphorylation dynamics) was monitored using fluorescence resonance energy transfer (FRET) microscopy. All the measurements were taken during, before and after the LIPUS exposure. Our experimental results clearly showed that the diffusion coefficients of macromolecules within the cell increased with acoustic pressure by 12.1 to 33.5 % during the sonication, and the increments were proportional to their molecular sizes regardless of the ultrasound frequency used. This observation in living cells was consistent with the GUVs exposed to the LIPUS, which indicated that the diffusivity increase was a passive physical response to the acoustic energy of LIPUS. Under the 1 MHz LIPUS exposure with 400 kPa, the passive nucleocytoplasmic transport of enhanced green fluorescent protein (EGFP) was accelerated by 21.4 %. With the same LIPUS exposure condition, both the diffusivity and phosphorylation of ERK induced by EGF treatment were significantly elevated simultaneously, which implied that LIPUS could also modify the kinase kinetics in the signal transduction process. Taken together, this study is the first attempt to uncover the physical link between LIPUS and the dynamics of intracellular macromolecules and related biological processes that LIPUS can possibly increase the diffusivity of intracellular macromolecules, leading to the changes in the basic cellular processes: passive nucleocytoplasmic transport and ERK. Our findings can provide a novel perspective that the mechanotransduction process that the intracellular region, in addition to the cell membrane, can convert the acoustic stimuli of LIPUS to biochemical signals.

The Effect of Spatial Velocity Gradients on Block-Matching Accuracy for Ultrasound Velocimetry

Block matching serves as the foundation for ultrasound velocimetry techniques such as blood speckle tracking and echo-particle image velocimetry. Any spatial velocity gradients (SVGs) inside a block-matching pair will result in tracking error, due to both the finite block size and the ultrasound point-spread-function. We assess, using an in silico sinusoidal flow phantom, the effect of SVG magnitude and beam-to-flow angle on block-matching bias and precision. Secondarily we assess the effect that SVGs have on velocimetry bias when using angled plane-wave compounding. The magnitude and angle of SVGs were varied by adjusting the wavelength and direction of a sinusoidal flow profile. Scatterers displaced by this flow profile were used for simulating ultrasound radio frequency data at discrete time points. After beamforming, the 2-D flow field was estimated using block matching. Two imaging sequences were tested, a single plane-wave and a three-angled plane-wave. Smaller sinusoidal flow wavelengths resulted in increased bias and reduced precision, revealing an inverse relationship between sinusoidal flow wavelength and tracking error, with median errors ranging from 69%-90% for the smallest flow wavelengths (highest SVGs) down to 3%-5% for the largest (lowest SVGs). The SVG angle was also important, in which lateral SVGs (with axially oriented flows) resulted in significant speckle decorrelation and high tracking errors in regions with high SVGs. Conversely, axial SVGs (laterally oriented flow) experienced higher bias in the peak velocity regions of the flow profile. Coherent compounding resulted in higher velocity errors than using a single transmission for lateral SVGs but not for axial SVGs. The highest SVGs that could be measured with ≤10% error was when the sinusoidal flow wavelength was less than 20 times the ultrasound pulse wavelength. The clinical significance is that the high SVGs present in high kinetic energy flows, such as severe carotid stenosis and aortic regurgitation, will limit the ability to accurately quantify the velocities in these flow structures.

Dual-frequency piezoelectric micromachined ultrasound transducer based on polarization switching in ferroelectric thin films

Due to its additional frequency response, dual-frequency ultrasound has advantages over conventional ultrasound, which operates at a specific frequency band. Moreover, a tunable frequency from a single transducer enables sonographers to achieve ultrasound images with a large detection area and high resolution. This facilitates the availability of more advanced techniques that simultaneously require low- and high-frequency ultrasounds, such as harmonic imaging and image-guided therapy. In this study, we present a novel method for dual-frequency ultrasound generation from a ferroelectric piezoelectric micromachined ultrasound transducer (PMUT). Uniformly designed transducer arrays can be used for both deep low-resolution imaging and shallow high-resolution imaging. To switch the ultrasound frequency, the only requirement is to tune a DC bias to control the polarization state of the ferroelectric film. Flextensional vibration of the PMUT membrane strongly depends on the polarization state, producing low- and high-frequency ultrasounds from a single excitation frequency. This strategy for dual-frequency ultrasounds meets the requirement for either multielectrode configurations or heterodesigned elements, which are integrated into an array. Consequently, this technique significantly reduces the design complexity of transducer arrays and their associated driving circuits.

Real-time cavitation monitoring based on the entropic analysis of ultrasound RF signals

The violent inertial cavitation activity generated in high intensity focused ultrasound (HIFU) treatment has a risk of damaging healthy tissues around the target area, so that it is necessary to monitor the degree of cavitation during the treatment. Entropy, as a non-model-based statistical parameter, can effectively characterize the effect of cavitation on the structure of scatters within tissues. Thus, a real-time cavitation monitoring system was established based on the entropy analysis of ultrasound radio frequency (RF) signals, and the degree of cavitation was evaluated through entropy images. Based on the two-dimensional average filtering method, we achieved real-time monitoring of cavitation through the reconstruction of entropy image and the binarization of cavitation regions, breaking the inherent limitation of current systems that can only perform cavitation monitoring between HIFU pulses. The results showed that the entropy image retained more frequency components, which could determine the time and location of cavitation earlier and display cavitation areas. Moreover, as the acoustic pressure increased, the advance of cavitation indication in the entropy images became earlier. This method might provide a feasible evaluation scheme for improving real-time cavitation monitoring during HIFU treatment and was expected to become an effective reference index for imaging in HIFU surgery.

Frequency shifting of transmitted ultrasound in thick composites containing fiber wrinkles and its application in non-destructive evaluation

Thick composite structures are prone to defects such as fiber wrinkles and voids during manufacturing. It is challenging to accurately evaluate the forming quality of the structures using conventional ultrasonic inspection, due to the coupling effects between time-frequency features of ultrasound and mixed-type defects. Propagation behaviors of through-thickness transmitted ultrasound in thick composites with fiber wrinkles, voids and no defects were comparatively investigated by both simulation and experiment in this study. Influence of out-of-plane fiber wrinkles on the ultrasonic frequency shifting was studied by comparing the time-frequency characteristics of simulated ultrasonic signals after propagating different distances in the intact and wavy composites. Changes of transmission coefficients of converted transverse waves caused by fiber wrinkles were concluded be the reason for the appearance of high-frequency components above the excitation frequency in the transmitted ultrasound signal. Thereby ultrasonic defect inspection indices based on the phenomenon of ultrasonic frequency shifting were defined. Effects of interaction angles between ultrasonic propagation direction and fibers on the defined inspection indices was further investigated quantitatively. The thick composites with diverse defects were successfully diagnosed using the ultrasound frequency shifting and energy dissipation behaviors.

Acoustically stimulated electromagnetic method for sensing electric and magnetic properties

A measurement technique for detecting acoustically induced polarization is introduced. Ultrasonic irradiation can generate alternating electric or magnetic polarization in materials via electromechanical or magnetomechanical coupling, respectively. It follows that electromagnetic fields are often emitted to the surrounding environment when materials are acoustically stimulated. The first harmonic response of the acoustically stimulated electromagnetic (ASEM) field is detected by a resonant antenna tuned to the ultrasound frequency. Ultrasound can temporally modulate the magnetic polarization (magnetization) in ferromagnetic materials, resulting in magnetic imaging and magnetic hysteresis measurements via ultrasonic stimulation. Ultrasonic probing of local magnetic properties gives unique magnetic measurements and is a promising tool in steel inspection. Furthermore, the ASEM response is generated in not only inorganic crystals but also biological tissues such as bones, tendons, and the aortic wall. The response signal is well explained by stress-induced electric polarization of biological tissues, which depends on the crystallinity of fibrous proteins. Therefore, the ASEM method opens possibilities for unique noninvasive sensing in medical fields. In this talk, we will discuss the origin of the ASEM response in various materials and its applications including steel and human measurements.

Dependence of sonoporation efficiency on microbubble size: An in vitro monodisperse microbubble study

Sonoporation is the process where intracellular drug delivery is facilitated by ultrasound-driven microbubble oscillations. Several mechanisms have been proposed to relate microbubble dynamics to sonoporation including shear and normal stress. The present work aims to gain insight into the role of microbubble size on sonoporation by varying the microbubble size of monodisperse microbubble suspensions. Sonoporation experiments were performed in vitro on cell monolayers at an ultrasound frequency of 1 MHz at varying acoustic pressures (250–750 kPa) and pulse length (10, 100, 1000 cycles). Sonoporation efficiency was quantified using flow cytometry by measuring the FITC-dextran (4 kDa and 2 MDa) fluorescence intensity in 10,000 cells per experiment. We demonstrate that the bubble oscillation amplitude is nearly independent of the equilibrium bubble radius at acoustic pressure amplitudes that induce sonoporation (≥500 kPa). However, we show that sonoporation efficiency is strongly dependent on the equilibrium bubble size and most efficiently induced by off-resonance 4.7-μm radius bubbles. These 4.7-μm bubbles are an order of magnitude more efficient than the polydisperse bubbles. We discuss that for our system shear stress is highly unlikely the mechanism of action, while we show that sonoporation efficiency correlates well with an estimate of the bubble-induced normal stress.