RESUMEN

Coal spontaneous combustion often wastes resources and causes environmental pollution. Rapid and accurate identification of high temperature areas in coal is essential to reducing such combustion and environmental pollution. The acoustic thermometry method has the benefits of large temperature measurement space, non-contact, and high interference resistance. Determining the attenuation characteristics of acoustic waves in loose coal is the basis and premise for realizing acoustic temperature measurement. Four types of bituminous coal were scanned by computer tomography equipment. A self-designed acoustic attenuation test device was used to test coal samples under different temperatures and particle sizes. The study result demonstrates that the distribution characteristics of loose coal voids are mainly related to the particle size. The smaller the particle size range, the more uniform the void distribution. As the size of the coal particles increases, the voids become larger. The acoustic attenuation coefficients of four coal samples showed an increasing trend as frequency increased. The influence of coal particle size distribution on the acoustic attenuation coefficient was greater than that of temperature and metamorphic degree. The peak values of coal sound attenuation for different particle sizes were around 400, 700, 1100, and 1600 Hz. This indicated that the distribution of voids was the main factor affecting the propagation of acoustic waves. By analysing the attenuation mechanism of the acoustic wave in loose coal, the attenuation of acoustic temperature measurement signal was caused by the combined effect of loose coal on acoustic wave absorption and scattering. The study results provide theoretical support for the realization of acoustic wave detection of high temperature point in loose coal spontaneous combustion.

RESUMEN

OBJECTIVE: Acoustic attenuation in the propagation path of focused ultrasound ablation surgery determines the energy loss toward the focal region and is critical to the consequent treatment outcomes. In situ non-invasive, reliable, and accurate measurement is challenging for multi-layered heterogeneous tissues within the focusing angle. METHODS: A novel measurement approach is proposed and its performance is evaluated using ex vivo porcine tenderloin and bovine heart. A big boiling bubble (i.e., larger than a few millimeters in size) was produced at the focus as a strong reflector inside the tissue, and the echo amplitudes were used to determine the acoustic attenuation. Two models, acoustic ray and energy loss, were developed to derive the equivalent acoustic attenuation coefficient for a focused beam. RESULTS: The measured acoustic attenuation coefficients of ex vivo porcine tenderloin and bovine heart at 0.97 MHz and a thickness of 3 cm are 0.159 ± 0.002 and 0.250 ± 0.005 Np/cm, respectively, which are all within the scope of measured values in the literature. In addition, the echo amplitude is sensitive to the conditions of the propagation path, and the inverse acoustic attenuation coefficient of the silicone gel pad placed in front of the tissue sample was 0.807 ± 0.002 Np/cm, which is comparable to the measurement using the insertion substitution method, 0.766 ± 0.003 Np/cm. CONCLUSION: Our proposed approach could determine the tissue acoustic attenuation for focused ultrasound ablation surgery reliably and accurately in situ. The easy operating protocol may allow clinical translation and adoption for improved safety and efficacy.

Asunto(s)

RESUMEN

For patients who are often embarrassed and uncomfortable when exposing their breasts and having them touched by physicians of different genders during auscultation, we are developing a robotic system that performs auscultation over clothing. As the technical issue, the sound obtained through the clothing is often attenuated. This study aims to investigate clothing-induced acoustic attenuation and develop a suppression method for it. Because the attenuation is due to the loss of energy as sound propagates through a medium with viscosity, we hypothesized that the attenuation is improved by compressing clothing and shortening the sound propagation distance. Then, the amplitude spectrum of the heart sound was obtained over clothes of different thicknesses and materials in a phantom study and human trial at varying contact forces with a developed passive-actuated end-effector. Our results demonstrate the feasibility of the attenuation suppression method by applying an optimum contact force, which varied according to the clothing condition. In the phantom experiments, the attenuation rate was improved maximumly by 48% when applying the optimal contact force (1 N). In human trials, the attenuation rate was under the acceptable attenuation (40%) when applying the optimal contact force in all combinations in each subject. The proposed method promises the potential of robotic auscultation toward eliminating gender bias.

Asunto(s)

RESUMEN

Ultrasound phantoms mimic the acoustic and mechanical properties of native tissues. Polyvinyl alcohol (PVA) phantoms are used extensively as models for validating ultrasound elastography approaches. However, the viscous properties of PVA phantoms have not been investigated adequately. Glycerol is a viscous liquid that has been reported to increase the speed of sound of phantoms. This study aims to assess the acoustic and viscoelastic properties of PVA phantoms and PVA mixed with glycerol at varying concentrations. The phantoms were fabricated with 10% w/v PVA in water with varying concentrations of glycerol (10%, 15% and 20% v/v) and 2% w/v silicon carbide particles as acoustic scatterers. The phantoms were subjected to either one, two, or three 24-h freeze-thaw cycles. The longitudinal sound speeds of all PVA phantoms were measured, and ranged from 1529 to 1660 m/s. Attenuation spectroscopy was performed in the range of 5 to 20 MHz. The measured attenuation followed a power-law relationship with frequency, wherein the power-law fit constants and exponents ranged from 0.02 to 0.1 dB/cm/MHzn and from 1.6 to 1.9, respectively. These results were in agreement with previous reports for soft tissues. Viscoelasticity of PVA phantoms was assessed using rheometry. The estimated values of shear modulus and viscosity using the Kelvin-Voigt and Kelvin-Voigt fractional derivative models were within the range of previously-reported tissue-mimicking phantoms and soft tissues. The number of freeze-thaw cycles were shown to alter the viscosity of PVA phantoms, even in the absence of glycerol. Scanning electron microscopy images of PVA phantoms without glycerol showed a porous hydrogel network, in contrast to those of PVA-glycerol phantoms with non-porous structure. Phantoms fabricated in this study possess tunable acoustic and viscoelastic properties within the range reported for healthy and diseased soft tissues. This study demonstrates that PVA phantoms can be manufactured with glycerol for applications in ultrasound elastography.

Asunto(s)

RESUMEN

Acoustic properties of biomaterials and engineered tissues reflect their structure and cellularity. High-frequency ultrasound (US) can non-invasively characterize and monitor these properties with sub-millimetre resolution. We present an approach to estimate the speed of sound, acoustic impedance, and acoustic attenuation of cell-laden hydrogels that accounts for frequency-dependent effects of attenuation in coupling media, hydrogel thickness, and interfacial transmission/reflection coefficients of US waves, all of which can bias attenuation estimates. Cell-seeded fibrin hydrogel disks were raster-scanned using a 40 MHz US transducer. Thickness, speed of sound, acoustic impedance, and acoustic attenuation coefficients were determined from the difference in the time-of-flight and ratios of the magnitudes of US signals, interfacial transmission/reflection coefficients, and acoustic properties of the coupling media. With this approach, hydrogel thickness was accurately measured by US, with agreement to confocal microscopy (r2 = 0.97). Accurate thickness measurement enabled acoustic property measurements that were independent of hydrogel thickness, despite up to 60% reduction in thickness due to cell-mediated contraction. Notably, acoustic attenuation coefficients increased with increasing cell concentration (p < 0.001), reflecting hydrogel cellularity independent of contracted hydrogel thickness. This approach enables accurate measurement of the intrinsic acoustic properties of biomaterials and engineered tissues to provide new insights into their structure and cellularity. STATEMENT OF SIGNIFICANCE: High-frequency ultrasound can measure the acoustic properties of engineered tissues non-invasively and non-destructively with µm-scale resolution. Acoustic properties, including acoustic attenuation, are related to intrinsic material properties, such as scatterer density. We developed an analytical approach to estimate the acoustic properties of cell-laden hydrogels that accounts for the frequency-dependent effects of attenuation in coupling media, the reflection/transmission of ultrasound waves at the coupling interfaces, and the dependency of measurements on hydrogel thickness. Despite up to 60% reduction in hydrogel thickness due to cell-mediated contraction, our approach enabled measurements of acoustic properties that were substantially independent of thickness. Acoustic attenuation increased significantly with increasing cell concentration (p < 0.001), demonstrating the ability of acoustic attenuation to reflect intrinsic physical properties of engineered tissues.

Asunto(s)

RESUMEN

Comprehensive characterization of biomedical imaging systems require phantoms that are easy to fabricate and can mimic human tissue. Additionally, with the arrival of engineered tissues, it is key to develop phantoms that can mimic bioengineered samples. In ultrasound and photoacoustic imaging, water-soluble phantom materials such as gelatin undergo rapid degradation while polymer-based materials such as polyvinyl alcohol are not conducive for generating bioengineered tissues that can incorporate cells. Here we propose silk protein-based hydrogels as an ultrasound and photoacoustic phantom material that has potential to provide a 3D environment for long-term sustainable cell growth. Common acoustic, optical, and biomechanical properties such as ultrasound attenuation, reduced scattering coefficient, and Young's modulus were measured. The results indicate that silk acoustically mimics many tissue types while exhibiting similar reduced optical scattering in the wavelength range of 400-1200 nm. Furthermore, silk-based materials can be stored long-term with no change in acoustic and optical properties, and hence can be utilized to assess the performance of ultrasound and photoacoustic systems.

RESUMEN

The traditional acoustic attenuation coefficient is derived from an analogy of the attenuation of an electromagnetic wave propagating inside a non-ideal medium, featuring only the attenuation of wave propagation. Nonetheless, the particles inside viscous solids have mass, vibrating energy, viscosity, and inertia of motion, and they go through transient and damping attenuation processes. Based on the long-wavelength approximation, in this paper, we use the energy conservation law to analyze the effect of the viscosity of the medium on acoustic attenuation. We derive the acoustic attenuation coefficient by combinations of the dynamical equation of a solid in an acoustic field with conventional longitudinal wave propagation under a spring oscillator model. Considering the attenuation of propagating waves and the damping attenuation of particle vibration, we develop a frequency dispersion relation of phase velocity for the longitudinal wave propagating inside viscous solid media. We find that the acoustic impulse response and vibrational system function depends on the physical properties of the viscous solid media and their internal structure. Combined with system function, the impulse response can be an excellent tool to invert the physical properties of solids and their internal structures. We select a well-known rock sample for analysis, calculate the impulse response and vibrational system function, and reveal new physical insight into creating acoustic attenuation and frequency dispersion of phase velocity. The results showed that the newly developed acoustic attenuation coefficients enjoy a substantial improvement over the conventional acoustic attenuation coefficients reported in the literature, which is essential for industrial applications; so are the dispersion characteristics.

RESUMEN

Thick films with nominal composition (K0.5Na0.5)0.99Sr0.005NbO3 (KNNSr) on porous ceramics with identical nominal composition were investigated as potential candidates for environmentally benign ultrasonic transducers composed entirely of inorganic materials. In this paper, the processing of the multilayer structure, namely, the thick film by screen printing and the porous ceramic by sacrificial template method, is related to their phase composition, microstructure, electromechanical, and acoustic properties to understand the performance of the devices. The ceramic with a homogeneous distribution of 8 µm pores had a sufficiently high attenuation coefficient of 0.5 dB/mm/MHz and served as an effective backing. The KNNSr thick films sintered at 1100 °C exhibited a homogeneous microstructure and a relative density of 97%, contributing to a large dielectric permittivity and elastic constant and yielding a thickness coupling factor kt of ~30%. The electroacoustic response of the multilayer structure in water provides a centre frequency of 15 MHz and a very large fractional bandwidth (BW) of 127% at -6 dB. The multilayer structure is a candidate for imaging applications operating above 15 MHz, especially by realising focused-beam structure through lenses to further increase the sensitivity in the focal zone.

RESUMEN

Medical implants are routinely tracked and monitored using different techniques, such as MRI, X-ray, and ultrasound. Due to the need for ionizing radiation, the two former methods pose a significant risk to tissue. Ultrasound imaging, however, is non-invasive and presents no known risk to human tissue. Aerogels are an emerging material with great potential in biomedical implants. While qualitative observation of ultrasound images by experts can already provide a lot of information about the implants and the surrounding structures, this paper describes the development and study of two simple B-Mode image analysis techniques based on attenuation measurements and echogenicity comparisons, which can further enhance the study of the biological tissues and implants, especially of different types of biocompatible aerogels.

RESUMEN

Cells incur structural and functional damage from external stimuli. Under scanning acoustic microscopy (SAM), speed of sound (SOS), attenuation, and thickness values are plotted to visualize cellular stiffness, viscosity, and size. The obtained digital data are then compared using statistical analysis. In the present study, we aimed to investigate the alterations in the mechanical and structural characteristics of cancer cells in response to anticancer drugs, acidic fluids, and microwave burdens using SAM. We found that active untreated cells showed increased thickness and reduced SOS and attenuation, whereas dying treated cells displayed reduced thickness and increased SOS. Tannic and acetic acid treatments and microwave irradiation all increased SOS and attenuation and reduced thickness, which meant that these treatments made cells thinner, stiffer, and more viscous. Furthermore, the different anticancer drugs interacted with cancer cells to induce characteristic changes in SAM values. These structural and mechanical alterations induced in cells were difficult to observe under light microscopy. However, under SAM, cancer cell activity and function corresponded consistently with changes in SAM values. Cellular damage parameters were statistically compared between the different treatments, and time-dependent cellular changes were established. SAM observation can therefore reliably evaluate cancer cell damage and recovery after chemotherapy and physical therapy. These results may help evaluate the therapeutic efficacy of various treatments.

RESUMEN

Ultrasound computed tomography (USCT) systems based on capacitive micromachined ultrasonic transducer (CMUT) arrays have a wide range of application prospects. For this paper, a high-precision image reconstruction method based on the propagation path of ultrasound in breast tissue are designed for the CMUT ring array; that is, time-reversal algorithms and FBP algorithms are respectively used to reconstruct sound speed distribution and acoustic attenuation distribution. The feasibility of this reconstruction method is verified by numerical simulation and breast model experiments. According to reconstruction results, sound speed distribution reconstruction deviation can be reduced by 53.15% through a time-reversal algorithm based on wave propagation theory. The attenuation coefficient distribution reconstruction deviation can be reduced by 61.53% through FBP based on ray propagation theory. The research results in this paper will provide key technological support for a new generation of ultrasound computed tomography systems.

RESUMEN

It is shown that, in spite of the wave radiation into the adjacent liquid, a large group of Lamb waves are able to propagate along piezoelectric plates (quartz, LiNbO3, LiTaO3) coated with a liquid layer (distilled water H2O). When the layer freezes, most of the group's waves increase their losses, essentially forming an acoustic response towards water-to-ice transformation. Partial contributions to the responses originating from wave propagation, electro-mechanical transduction, and wave scattering were estimated and compared with the coupling constants, and the vertical displacements of the waves were calculated numerically at the water-plate and ice-plate interfaces. The maximum values of the responses (20-30 dB at 10-100 MHz) are attributed to the total water-to-ice transformation. Time variations in the responses at intermediate temperatures were interpreted in terms of a two-phase system containing both water and ice simultaneously. The results of the paper may turn out to be useful for some applications where the control of ice formation is an important problem (aircraft wings, ship bodies, car roads, etc.).

RESUMEN

This paper investigates the shell elastic properties and the number-concentration stability of a new acoustofluidic delivery agent liposome in comparison to Definity™, a monolayer ultrasonic contrast agent microbubble. The frequency dependent attenuation of an acoustic beam passing through a microbubble suspension was measured to estimate the shell parameters. The excitation voltage was adjusted to ensure constant acoustic pressure at all frequencies. The pressure was kept at the lowest possible magnitude to ensure that effects from nonlinear bubble behaviour which are not considered in the analytical model were minimal. The acoustofluidic delivery agent shell stiffness Sp and friction Sf parameters were determined as (Sp = 0.11 N/m, Sf = 0.31 × 10-6 Kg/s at 25 °C) in comparison to the Definity™ monolayer ultrasound contrast agent which were (Sp = 1.53 N/m, Sf = 1.51 × 10-6 Kg/s at 25 °C). When the temperature was raised to physiological levels, the friction coefficient Sf decreased by 28% for the monolayer microbubbles and by only 9% for the liposomes. The stiffness parameter Sp of the monolayer microbubble decreased by 23% while the stiffness parameter of the liposome increased by a similar margin (27%) when the temperature was raised to 37 °C. The size distribution of the bubbles was measured using Tunable Resistive Pulse Sensing (TRPS) for freshly prepared microbubbles and for bubble solutions at 6 h and 24 h after activation to investigate their number-concentration stability profile. The liposome maintained >80% of their number-concentration for 24 h at physiological temperature, while the monolayer microbubbles maintained only 27% of their number-concentration over the same period. These results are important input parameters for the design of effective acoustofluidic delivery systems using the new liposomes.

Asunto(s)

RESUMEN

A soundwave is transmitted by adjacent molecules in the medium, and depending on the type of sound, it exhibits various characteristics such as frequency, sound pressure, etc. If the acoustic wavelength of the soundwave is sufficiently long compared with the size of an acoustic element, physical analysis within the sound element could be simplified regardless of the shape of the acoustic element: this is called "long wavelength approximation". A Helmholtz resonator, a representative acoustic element which satisfies the "long wavelength theory", consists of a neck part and a cavity part. The Helmholtz resonators can absorb certain frequencies of sound through resonance. To exhibit attenuation properties at ultrasound range, the Helmholtz resonator should be made into a microscale since Helmholtz resonators should satisfy the "long wavelength approximation". In this study, Helmholtz resonator inspired acoustic elements were fabricated using MEMS technology, and acoustic attenuation experiments in a water bath were conducted using various shapes and materials. As a result, the fabricated samples showed admirable attenuation properties up to ~13 dB mm-1 at 1 MHz. The results were analyzed to derive the necessary conditions for the fabrication of acoustic elements with acoustic attenuation properties in ultrasound range.

RESUMEN

The spatial resolution achievable in photoacoustic imaging decreases with the imaging depth, resulting in blurred images for deeper structures. Apart from technical limitations, the ultimate resolution limit results from the second law of thermodynamics. The attenuation of the optically generated acoustic waves on their way from the imaged structure to the sample surface by scattering and dissipation leads to an increase of entropy. The resulting loss of spatial resolution for structures embedded in attenuating media can be compensated by numerical methods that make use of additional available information. In this article, we demonstrate this using experimental data from plane one-dimensional (1D) acoustic waves propagating in fat tissue. The acoustic waves are optically induced by nanosecond laser pulses and measured with piezoelectric transducers. The experimental results of 1D compensation are also relevant for photoacoustic imaging in 2D or 3D in an acoustically attenuating medium by dividing the reconstruction problem into two steps: First, the ideal signal, which is the solution of the un-attenuated wave equation, is determined by the proposed 1D attenuation compensation for each detector signal. In a second step, any ultrasound reconstruction method for un-attenuated data can be used for image reconstruction. For the reconstruction of a small step milled into a silicon wafer surface, which allows the generation of two photoacoustic pulses with a small time offset, we take advantage of non-negativity and sparsity and inverted the measured, frequency dependent acoustic attenuation of the fat tissue. We were able to improve the spatial resolution for imaging through 20 mm of porcine fat tissue compared to the diffraction limit at the cut-off frequency by at least a factor of two.

RESUMEN

Ultrasound is a method for enhancing neurite outgrowth because of its thermal effect. In order to reach the working temperature to enhance neurite outgrowth, long-time treatment by ultrasound is necessary, while acknowledging that the treatment poses a high risk of damaging nerve cells. To overcome this problem, we developed a method that shortens the ultrasonic treatment time with a warming biomaterial. In this study, we used Fe3O4 nanoparticle-embedded polycaprolactone (PCL) as a sonosensitized biomaterial, which has an excellent heating rate due to its high acoustic attenuation. With this material, the ultrasonic treatment time for enhancing neurite outgrowth could be effectively shortened. Ultrasonic treatment could also increase neuronal function combined with the warming biomaterial, with more promoter neuronal function than only ultrasound. Moreover, the risk of overexposure can be avoided by the use of the warming biomaterial by reducing the ultrasonic treatment time, providing better effectiveness.

Asunto(s)

RESUMEN

OBJECTIVE: A cellulose-derived nano-toolbox has been developed via the chemical nano-trimming of electrosterically stabilized nanocrystalline celluloses (ENCCs). ENCC is a member of the class of hairy nanocellulose (HNC). The objective of this study is to determine the properties of chemically trimmed HNCs in order to establish whether or not they overcome the surface chemistry and size restrictions of conventional nanocelluloses. The newly "so-called crew-cut ENCCs" emerged by this approach address many technological and environmental challenges in colloidal systems, i.e., drug delivery, anti-scaling and self-assembly. Despite the importance of the crew-cut species, little is known about the systematic changes and the underlying mechanisms of the trimming of their hairs (the chains protruding from both ends of the cylindrical core). EXPERIMENTS: To quantify the effect of the hair trimming on the charge density as well as the kinetics of this process, the carboxylic acid content is determined by conductometric titration as a function of time and reaction conditions. We use electro-acoustic spectroscopy to elucidate the differences in colloidal properties of various crew-cut ENCCs. We focus on the interplay between the time of the acid-catalyzed hydrolysis reaction and tunable parameters, such as size and surface electric charge of ENCC, as well as their microrheological behavior. FINDINGS: We show that a range of hairy ENCCs with various sizes and charge densities is easily obtained by taking advantages of the preferential hydrolysis of the amorphous chains protruding from both ends of the nanocrystals. The trimming mediated by a HCl-catalyzed hydrolysis is initially very fast, but slows down subsequently. The formation of crew-cut species with a smaller particle size and zeta potential was electro-acoustically verified by increasing the reaction time. The longitudinal viscosities of the trimmed ENCC suspensions also decreased with prolonging the reaction time. This research shows how manipulating HNCs enables both scientists and technologists to access a collection of nanocrystals with desired colloidal properties, based on the most abundant biopolymer in the world.

RESUMEN

Acoustic properties of biological tissues usually vary inhomogeneously in space. Tissues with different chemical composition often have different acoustic properties. The assumption of acoustic homogeneity may lead to blurred details, misalignment of targets and artifacts in the reconstructed photoacoustic tomography (PAT) images. This paper summarizes the main solutions to PAT imaging of acoustically heterogeneous tissues, including the variable sound speed and acoustic attenuation. The advantages and limits of the methods are discussed and the possible future development is prospected.

Asunto(s)

RESUMEN

Although transcranial photoacoustic imaging has been previously investigated by several groups, there are many unknowns about the distorting effects of the skull due to the impedance mismatch between the skull and underlying layers. The current computational methods based on finite-element modeling are slow, especially in the cases where fine grids are defined for a large 3-D volume. We develop a very fast modeling/simulation framework based on deterministic ray-tracing. The framework considers a multilayer model of the medium, taking into account the frequency-dependent attenuation and dispersion effects that occur in wave reflection, refraction, and mode conversion at the skull surface. The speed of the proposed framework is evaluated. We validate the accuracy of the framework using numerical phantoms and compare its results to k-Wave simulation results. Analytical validation is also performed based on the longitudinal and shear wave transmission coefficients. We then simulated, using our method, the major skull-distorting effects including amplitude attenuation, time-domain signal broadening, and time shift, and confirmed the findings by comparing them to several ex vivo experimental results. It is expected that the proposed method speeds up modeling and quantification of skull tissue and allows the development of transcranial photoacoustic brain imaging.

RESUMEN

Acoustic properties of biological tissues usually vary inhomogeneously in space. Tissues with different chemical composition often have different acoustic properties. The assumption of acoustic homogeneity may lead to blurred details, misalignment of targets and artifacts in the reconstructed photoacoustic tomography (PAT) images. This paper summarizes the main solutions to PAT imaging of acoustically heterogeneous tissues, including the variable sound speed and acoustic attenuation. The advantages and limits of the methods are discussed and the possible future development is prospected.

Asunto(s)