Simulation of ultrasonically induced electrical potentials in bone

Low-intensity pulsed ultrasound treatment is known to shorten the healing period of bone fractures by 30%-40%, but the initial mechanism of the healing process remains unknown. One possible mechanism is related to the piezoelectricity of bone. However, the complex geometry of bones results in inherent challenges to evaluating electric fields induced therein. Therefore, in this study, we investigate the piezoelectric responses of bones by using simulations to study the wave propagation and induced potentials in bone, according to the piezoelectric finite-difference time-domain (PE-FDTD) method. First, we verify the suitability of the PE-FDTD method by comparing the simulated electric field results with the experimental data obtained by an ultrasound receiver using bone as the piezoelectric element. Next, ultrasound irradiation into a real bone model (the radius of a 66-year-old woman) is simulated at different incident angles. At normal incidence and off-axis incidence (45°), the maximum electric field strength was 4.3 and 5.6 mV/cm, respectively. We also present evidence of significant shear wave contribution to the induced potential. The results of this study confirm the existence of ultrasonically induced potentials in heterogenous bones with complex shapes, equal in magnitude to potentials generated in electrically stimulated bone healing.

Precise Observation of Ultrasonic Pulses Using an SPR Sensor

Surface plasmon resonance (SPR) type ultrasonic sensors enable local measurements and have a flat frequency response in a wide frequency range. They are expected to be used in photoacoustic microscopy (PAM) and other applications that require broadband ultrasonic detection. In this study, we focus on the precise measurement of ultrasound pressure waveforms via a Kretschmann-type SPR sensor. The noise equivalent pressure was estimated to be 52 Pa [Formula: see text], and the maximum amplitude of the wave measured via the SPR sensor linearly responded to the pressure until 427 kPa [Formula: see text]. Furthermore, the observed waveform for each applied pressure agreed well with the waveforms measured via the calibrated ultrasonic transducer (UT) in the MHz range. Moreover, we focused on the effect of the sensing diameter on the frequency response of the SPR sensor. The results show that the beam diameter reduction improved the frequency response at high frequencies. Evidently, we found that the sensing diameter of the SPR sensor must be carefully selected in consideration of the measurement frequency.

Development of evaluation system for cerebral artery occlusion in emergency medical services: noninvasive measurement and utilization of pulse waves

Rapid reperfusion therapy can reduce disability and death in patients with large vessel occlusion strokes (LVOS). It is crucial for emergency medical services to identify LVOS and transport patients directly to a comprehensive stroke center. Our ultimate goal is to develop a non-invasive, accurate, portable, inexpensive, and legally employable in vivo screening system for cerebral artery occlusion. As a first step towards this goal, we propose a method for detecting carotid artery occlusion using pulse wave measurements at the left and right carotid arteries, feature extraction from the pulse waves, and occlusion inference using these features. To meet all of these requirements, we use a piezoelectric sensor. We hypothesize that the difference in the left and right pulse waves caused by reflection is informative, as LVOS is typically caused by unilateral artery occlusion. Therefore, we extracted three features that only represented the physical effects of occlusion based on the difference. For inference, we considered that the logistic regression, a machine learning technique with no complex feature conversion, is a reasonable method for clarifying the contribution of each feature. We tested our hypothesis and conducted an experiment to evaluate the effectiveness and performance of the proposed method. The method achieved a diagnostic accuracy of 0.65, which is higher than the chance level of 0.43. The results indicate that the proposed method has potential for identifying carotid artery occlusions.

Clinical application of endoscopic soft palate augmentation in the treatment of velopharyngeal insufficiency

Velopharyngeal structure augmentation with the injection of autologous fat tissue into the nasal mucosa of the soft palate has been reported previously. However, as the injection points in the velopharyngeal space cannot be observed directly, these injections may be difficult to perform accurately. This report describes a new endoscope-assisted approach in which the materials for velopharyngeal structure augmentation are administered while observing the injection points directly, also enabling adjustment of the amount of material injected. A case series of five patients aged 8-16 years who underwent endoscopic soft palate augmentation under general anaesthesia is reported. Autologous fat tissue was injected into the nasal mucosa of the soft palate using a needle-type device of an endoscope, and the effects of the treatment were evaluated. The injections were performed successfully, and the velopharyngeal function was improved. This new technique of endoscopy-assisted augmentation was useful for the treatment of velopharyngeal insufficiency.

Concentration-Dependent Viscoelasticity of Poloxamer-Shelled Microbubbles

The oscillation of shelled microbubbles during exposure to ultrasound is influenced by the mechanical properties of the shell components. The oscillation behavior of bubbles coated with various phospholipids and other amphiphiles has been studied. However, there have been few investigations of how the adsorption conditions of the shell molecules relate to the viscoelastic properties of the shell and influence the oscillation behavior of the bubbles. In the present study, we investigated the oscillation characteristics of microbubbles coated with a poloxamer surfactant, that is, Pluronic F-68, at several concentrations after the adsorption kinetics of the surfactant at the gas-water interface had reached equilibrium. The dilatational viscoelasticity of the shell during exposure to ultrasound was analyzed in the frequency domain from the attenuation characteristics of the acoustic pulses propagated in the bubble suspension. At Pluronic F-68 concentrations lower than 2.0 × 10^-2 mol L^-1, the attenuation characteristics typically exhibited a sharp peak. At concentrations higher than 2.0 × 10^-2 mol L^-1, the peak flattened. The dilatational elasticity and viscosity of the shell were estimated by fitting the theoretical model to the experimental values, which revealed that both the elasticity and viscosity increased markedly at approximately 2.0 × 10^-2 mol L^-1. This suggests that the adsorption properties of Pluronic F-68 strongly affect the oscillation characteristics of microbubbles of a size suitable for medical ultrasound diagnostics.

Control of the surface profile of powder using the flexural vibration of a V-shaped plate

In the pharmaceutical field, a technique to level the surface of powdered medicines is important in the dispensing process because the flatness of the powder surface affects the packaging accuracy directly. This paper investigates a method for leveling of the surface profile of powder using ultrasound vibration on a plate. The system used comprises a V-shaped plate and two ultrasound transducers, and the plate configuration required was determined from the results of simulations performed by finite element analysis. The resonant longitudinal vibration of the transducers generated the resonant flexural vibration mode of the plate at 27.4 kHz, which resulted in transportation and leveling of the powder. The powder was aggregated at the nodal positions of the flexural standing wave, and a correlation was observed between the sound pressure distribution over the plate and the surface profile of the powder. The powder leveling accuracy was investigated by varying the driving phase difference between the transducers, and it was found that a smaller standing wave ratio for the flexural vibration produced higher leveling accuracy. When the input voltage to the transducers was increased, the leveling time decreased and the leveling accuracy improved; the highest leveling accuracy obtained was 2.2 mm at 130 V_pp.

Varifocal Concave-Convex Lens Using Viscoelastic Gel and Ultrasound Vibration

A varifocal concave-convex lens using ultrasound and transparent viscoelastic gel is reported. The configuration of the lens is simple and thin, consisting of four pieces of a piezoelectric ultrasound transducer, a glass disk, and a transparent silicone gel film. It uses a combination of the ultrasound resonant flexural standing- and traveling-wave modes excited by in-phase and four-phase drives so that the lens can change its shape to both concave and convex by switching the resonance mode with the same structure. The acoustic radiation force (ARF) originated from the resonant flexural vibration modes changed the surface profile of the gel. Convex and concave deformation were generated at the center of the lens at the resonance frequencies of 38 and 60 kHz, respectively, indicating that a varifocal concave-convex lens could be fabricated by controlling the driving frequency, voltage amplitude, and phase differences among the ultrasound transducers. The deformational displacement on the lens surface and the change in the focal length increased with the input voltage amplitude. The optical microscopic images observed through the lens were enlarged 1.28× (reduced 0.92× ) in the convex (concave) mode with 20 [Formula: see text]. The response time for focusing and the temperature stability under operation were evaluated. By switching the resonance vibration modes of the lens through the input signals to multiple ultrasound transducers, the variable-focus function with both concave and convex lenses was achieved in the same configuration.

Study on ultrasonic wave propagation in equine leg bone for screening bucked shin

For simple, safe, portable, and inexpensive evaluation suitable for leg bone diseases of racehorses in the field, an ultrasonic measurement technique was applied to evaluate wave velocities. A digital model of the third metacarpal bone with the bucked shin was fabricated using high-resolution peripheral quantitative computerized tomography data of a racehorse. This model was anisotropic and heterogeneous, and was constructed using the measured ultrasonic wave velocities in the bone. With this model, ultrasonic wave propagation along the bone axis was simulated using the elastic finite-difference time-domain method. We found two main waves with different propagation velocities. The fast-waves showed a wave velocity close to the longitudinal wave in the axial direction. However, the apparent velocities changed dramatically owing to bone surface irregularities (changes of the shape) in the area of bucked shin. The slow-waves showed a wave velocity close to the shear wave, which was unaffected by the bone surface irregularities. The simple comparison of different wave behaviors may be a suitable parameter for the initial in vivo screening of bucked shin in the legs of racehorses, which can be performed in the field.

Signal Amplification of the Transient Response Measured by the Subnanosecond Pump-Probe Method Based on Surface Plasmon Resonance

A pump-probe system with a subnanosecond pulsed laser is expected to be a compact and inexpensive transient spectroscopic system that enables nondestructive and noncontact evaluations of the physical properties. However, an improvement in the sensitivity and a theoretical model to complement the measurement signal are necessary to obtain the transient signal precisely because of the low sensitivity and large time resolution. We have developed a highly sensitive pump-probe system with a subnanosecond pulsed laser that combines signal amplification based on surface plasmon resonance (SPR) in this study. An integrated theoretical model of the transient response obtained by a subnanosecond pump-probe under the SPR condition was proposed. Our model consisted of the profile descriptions of the used pulse source, temperature change, generated thermoelastic stress, estimated permittivity change in the metal film, and estimated reflectivity change. The theoretical estimations in the time domain and the incident angle dependence were compared with those of the experimental results to verify our theory. As a result, the estimations were well in agreement with the experimental results. Moreover, the signal-amplification mechanism based on SPR was discussed using our theory. The amplification was caused by the broadening of the resonant curve of SPR and the shift of the resonant angle, which seemed to come from the increase in the electron-phonon scattering rate and the thermal expansion of the metal film, respectively. A clear mechanism of SPR-based signal amplification of the subnanosecond pump-probe was identified through experimental and theoretical approaches.

Ultrasound liquid crystal lens with a variable focus in the radial direction for image stabilization

New technologies for adaptive optics are becoming increasingly important for miniature devices such as cell-phone cameras. In particular, motion-free autofocusing and optical image stabilization require sophisticated approaches for alternative lens architectures, materials, and processing to replace multiple solid elements. We discuss a new method, to the best of our knowledge, that provides image stabilization via an annular piezoelectric ceramic that uses ultrasound to drive a liquid crystal layer sandwiched between two circular glass substrates. The piezoelectric ceramic is divided into four quadrants that are independently driven with sinusoidal voltages at the resonant frequency of the lens. The technique is based on ultrasound vibrations with a suitable driving scheme. The lens configuration was modeled via finite-element analysis. Various combinations of the four-channel ultrasound transducer can be used to define the focal point of the liquid crystal lens. Clear optical images could be obtained with the lens. By using two-dimensional fast Fourier transforms, the focal point position was defined and shifted in the radial direction.

Simulation study on the effects of cancellous bone structure in the skull on ultrasonic wave propagation

The transcranial Doppler method (TCD) enables the measurement of cerebral blood flow velocity and detection of emboli by applying an ultrasound probe to the temporal bone window, or the orbital or greater occipital foramina. TCD is widely used for evaluation of cerebral vasospasm after subarachnoid hemorrhage, early detection of patients with arterial stenosis, and the assessment of brain death. However, measurements often become difficult in older women. Among various factors contributing to this problem, we focused on the effect of the diploe in the skull bone on the penetration of ultrasound into the brain. In particular, the effect of the cancellous bone structure in the diploe was investigated. Using a 2D digital bone model, wave propagation through the skull bone was investigated using the finite-difference time-domain (FDTD) method. We fabricated digital bone models with similar structure but different BV/TV (bone volume/total volume) values in the diploe. At a BV/TV of approximately 50–60% (similar to that of older women), the minimum ultrasound amplitude was observed as a result of scattering and multiple reflections in the cancellous diploe. These results suggest that structural changes such as osteoporosis may be one factor hampering TCD measurements.

Decrease in Longitudinal Wave Velocity in Glycated Collagen

Diabetic patients have a higher risk of bone fracture than those without diabetes, despite a normal bone mineral density. This higher riskmay result fromthe deterioration of collagen because of glycation. The objective of this study was to investigate the elastic properties of glycated collagen using the micro-Brillouin scattering technique. Using single-layer uniaxial collagen films with a thickness of approximately [Formula: see text], the longitudinal wave velocities, propagating in the parallel andperpendiculardirectionswith respect to the collagen fiber orientation, were measured in dry and wet film specimens. The wave velocities in the glycated collagen specimens decreased as a function of glycation time. This decrease depended on the direction of collagen fiber alignment and wave propagation. The lowest velocity due to glycation in thewet filmswas foundwhen the ultrasound propagated perpendicular to the fiber direction. These results indicate that the glycation of collagen in the bone may also reduce bone elasticity and suggest that the effects of glycation on collagen films may be anisotropic.

Varifocal optical lens using ultrasonic vibration and thixotropic gel

A variable focus optical lens using a thixotropic gel and ultrasonic vibration is discussed. The surface profile of the gel could be deformed via acoustic radiation force generated by ultrasound. A thixotropic gel in which the viscosity was changed by shear stress was employed as a transparent lens material. The thixotropic gel allowed the lens to maintain shape deformation in the absence of continuous ultrasound excitation. The lens had a simple structure with no mechanical moving parts and included an annular piezoelectric transducer, a glass disk, and the thixotropic gel film. The axisymmetric concentric flexural vibration mode was generated on the lens at 71 kHz, which resulted in static surface deformation of the gel via the acoustic radiation force. The preservation rate was investigated after switching off the ultrasonic excitation. There was a trade-off between the preservation rate of the lens deformation and the response time for focusing. The focal length could be controlled via the input voltage to the lens, and a variable-focus convex lens could be realized; the change in the focal length with 4.0 V_pp was 0.54 mm. The optical transmittance of the lens was measured and the transmittance ranged 70%-80% in the visible spectral region.

Ultrasound liquid crystal lens with enlarged aperture using traveling waves

A new type of ultrasonically controlled concave liquid crystal lens based on traveling waves (TWs) with a divided electrode structure and an appropriate driving scheme is proposed in this Letter. The lens uses an annular piezoelectric ceramic divided into four parts for four-phase driving and consists of a liquid crystal layer in a sandwich structure between two circular glass substrates. The lens configuration was simulated by finite element analysis using the Ansys software. Here we discuss the use of TWs to expand the lens aperture and clarify the lens' optical characteristics using a Shack-Hartmann wavefront sensor. The effective lens aperture using TWs was 4.4 mm, and the focal length was 3.8 m.

Anisotropic Longitudinal Wave Propagation in Swine Skull

To understand the in-plane elastic character of ultrasonic waves in the skull, longitudinal wave velocities were studied in the MHz range using a conventional pulse technique. Taking advantage of the thickness of swine skulls, anisotropic in-plane wave velocity changes in the outer and diploe layers were experimentally investigated using structural information measured by X-ray computer tomography (CT). The velocities in the thin inner layer were difficult to measure. The main trabecular alignment (MTA) in the thick swine diploe layer was almost perpendicular to the thickness direction and changed with position inside the skull. The degree of anisotropy of in-plane longitudinal wave velocity ranged 1.07-1.33 in both outer and diploe layers, depending on position and swine sample. The angle of the fastest velocity in the outer layer was different from that in most parts of the diploe layer. Anisotropic character in the diploe layer gradually changed with position in the thickness direction.

Site dependence of ultrasonically induced electrical potentials in bone

The success rate of low-intensity pulsed ultrasound (LIPUS) therapy depends on the bone site. However, the initial mechanism of physical stimulation by ultrasound and bone cellular response remains unclear. One possible physical stimulation is the induced electrical potentials due to the piezoelectricity. In this study, the output electrical potentials of ultrasound transducers made from bovine bones were investigated. Transducers made from the radius bone showed the largest electric potentials, followed by tibia, femur, and humerus. There was clear site dependence of the induced electric potentials of bone, in good accordance with the success rate of LIPUS therapy.

Growth of cortical bone thickness and trabecular bone density in Japanese children

BACKGROUND

The acquisition of a high bone density at a young age is a strategy to prevent fractures/falls later in life. We therefore decided to investigate the increases in cortical thickness (CoTh) and trabecular bone density (TBD) of children.

METHODS

Subjects comprised 1314 students (678 boys and 636 girls) aged between 12 and 18 years. Lifestyle factors were examined with a self-administered questionnaire (sleep times, exercise habits, and calcium intake). Bone growth was assessed based on CoTh and TBD using an ultrasonic bone densitometer. Height, weight, and body fat percentage were also measured.

RESULTS

Increases in CoTh and TBD occurred earlier in girls than in boys. Calcium intake was not sufficient at any of the ages examined, and sleep times were shorter than those recommended by the National Sleep Foundation. Increases in CoTh and TBD occurred subsequent to increases in height. Although increases in CoTh were observed with age in both sexes, TBD increased in boys until the age of 17 years and in girls until the age of 15 years. At 18 years of age, the young adult mean value was greater than 100% for CoTh but lower than 100% for TBD. A multivariate analysis identified age, body mass index (BMI), and exercise as independent positive factors for CoTh, while body fat percentage was an independent negative factor. Age and BMI were independent positive factors for TBD in both sexes, whereas body fat percentage was a positive factor in boys only.

CONCLUSIONS

The study found that CoTH and TBD varied with age and differed in increase in boys and girls; related factors of bone increase could also be found. The results of this study may contribute to the acquisition of high bone density in children and adolescents.

Multimodal Evaluation of the Spatiotemporal Variations of Periprosthetic Bone Properties

Titanium implants are widely used in dental and orthopedic surgeries. However, implant failures still occur because of a lack of implant stability. The biomechanical properties of bone tissue located around the implant need to be assessed to better understand the osseointegration phenomena and anticipate implant failure. The aim of this study was to explore the spatiotemporal variation of the microscopic elastic properties of newly formed bone tissue close to an implant. Eight coin-shaped Ti6Al4V implants were inserted into rabbit tibiae for 7 and 13 weeks using an in vivo model allowing the distinction between mature and newly formed bone in a standardized configuration. Nanoindentation and micro-Brillouin scattering measurements were carried out in similar locations to measure the indentation modulus and the wave velocity, from which relative variations of bone mass density were extracted. The indentation modulus, the wave velocity and mass density were found to be higher (1) in newly formed bone tissue located close to the implant surface, compared to mature cortical bone tissue, and (2) after longer healing time, consistently with an increased mineralization. Within the bone chamber, the spatial distribution of elastic properties was more heterogeneous for shorter healing durations. After 7 weeks of healing, bone tissue in the bone chamber close to the implant surface was 12.3% denser than bone tissue further away. Bone tissue close to the chamber edge was 16.8% denser than in its center. These results suggest a bone spreading pathway along tissue maturation, which is confirmed by histology and consistent with contact osteogenesis phenomena.

Prolonged Hyperglycemia Reduces Elasticity of Type II Diabetic Rat Bone

An increase in bone fracture risk has been reported in patients with diabetes. To evaluate an early effect of glucose intolerance on bone homeostasis, we have characterized bones from spontaneously diabetic torii (SDT) rats, an animal model of type 2 diabetes in comparison with Sprague Dawley (SD) rats as healthy control. Focusing on early effects of diabetes on bone elasticity, longitudinal wave velocities of animal bones were first determined by a micro-Brillouin scattering technique in a non-destructive way. Wave velocities in the cortical and cancellous bones in the tibias of the SDT and SD rats were compared. In a pre-diabetic stage at approximately 10 weeks of age, there seems no significant difference in wave velocities in bones from age-matched SDT and SD rats. By contrast, after the onset of diabetes at approximately 20 weeks of age, the mean velocities of bones from SDT rats were lower than those of SD rat. In addition, the X-ray CT showed that the bone amounts of SDT rats were smaller than those of SD rats in an early diabetic stage at 20 weeks of age. The current study demonstrated that the wave velocity decreased in bones of SDT rats in the early stages of diabetes. While a decrease of bone strength in an early stage of diabetes can be partially explained from decreases in bone amount as well as bone elasticity, further studies will be needed in understanding a detailed mechanism of bone deterioration due to diabetes.

Piezoelectric and Inversely Piezoelectric Responses of Bone Tissue Plates in the Megahertz Range

Piezoelectricity in bone is thought to be a mechanism by which ultrasound promotes the healing of bone fractures. However, a few studies have been conducted in the more clinically relevant megahertz range. To understand the piezoelectricity in bone, we fabricated ultrasound transducers using bone samples as piezoelectric materials and identified the longitudinal ultrasound radiation and reception in the megahertz range. The maximum transmitting sensitivity of the bone transducer was 140 mPa/V, which was nearly 1/1000 of a polyvinylidene difluoride (PVDF) transducer that has better electrical properties and piezoelectricity. The resonance frequencies of the transducer depend on the plate thickness and angle between the bone axis (alignment direction of the hydroxyapatite crystallites) and ultrasound propagation direction, reflecting the anisotropic character of the bone. The reception and transmission sensitivities of the bone transducers also depend on the plate thickness and angle, showing maximum values at off-axis angles. These results indicate the existence of both piezoelectricity and inverse piezoelectricity in bone, which may be key factors in understanding the bone healing by low-intensity biophysical (electrical or mechanical) stimulation.

Molecular Orientation in a Variable-Focus Liquid Crystal Lens Induced by Ultrasound Vibration

A method to estimate orientation direction of liquid crystal molecules three-dimensionally under ultrasound excitation was proposed and the relationship between the ultrasound vibration and the molecular orientation was discussed. Our group have reported a technique to control orientation direction of liquid crystal molecules using ultrasound vibration which could be applied to an optical variable-focus liquid crystal lens. The lens consisted of a liquid crystal layer sandwiched by two glass circular discs and a piezoelectric ring. Ultrasound vibration induces change in the refractive index of the lens, enabling the variable-focus function. The three-dimensional orientation direction of the liquid crystal molecules in the lens was predicted from the transmitted light distributions under the crossed Nicol conditions. The liquid crystal molecules were inclined from vertical alignment by the ultrasound vibration, and larger ultrasound vibration gave larger inclination of the molecules. There was a strong correlation between the distributions of ultrasound vibration and the liquid crystal molecular orientation; the molecular orientation was changed remarkably between the antinodal and nodal parts of the ultrasound flexural vibration on the glass plate and the molecules aligned towards the antinode.

Control of the Surface Profile of a Thixotropic Fluid With Ultrasound

The viscosity and the surface profile of a thixotropic gel were controlled via ultrasound vibrations. The ultrasound device consisted of two piezoelectric lead zirconate titanate transducers glued to each end of a 60-mm-long rectangular glass substrate. It generated a 71-kHz flexural standing wave along the length. A 0.9-mm-thick thixotropic gel film made from silicone oil and hydrophobic fumed silica was formed on the glass substrate. The ultrasound vibration decreased the film viscosity, and its surface profile could be changed by the acoustic radiation force acting from the gel to the surrounding air, generated by the flexural vibration of the substrate. The transient response of the surface profile was observed by switching the ultrasound excitation ON and OFF. When the excitation was switched OFF, the gel displacement gradually decreased, but the surface profile did not return to that of the initial steady state, indicating that the viscosity recovered in time to preserve the surface profile. When a pulsed megahertz (MHz) signal was used to control the gel deformation, the surface profile rapidly approached the initial steady-state profile after the excitation.

Vibration Characteristics and Persistence of Poloxamer- or Phospholipid-Coated Single Microbubbles under Ultrasound Irradiation

Microbubbles shelled with soft materials are expected to find applications as ultrasound-sensitive drug delivery systems, including through sonoporation. Microbubbles with specific vibrational characteristics and long intravascular persistence are required for clinical uses. To achieve this aim, the kinetics of the microbubble shell components at the gas/liquid interface while being subjected to ultrasound need to be better understood. This paper investigates the vibration characteristics and lifetime of single microbubbles coated with a poloxamer surfactant, Pluronic F-68, and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) under ultrasound irradiation. Air- and perfluorohexane (PFH)-filled microbubbles coated with Pluronic F-68 and DMPC at several concentrations (0 to 10^-2 mol L^-1) were produced. An optical measurement system using a laser Doppler vibrometer and microscope was used to observe the radial vibration mode of single microbubbles. The vibrational displacement amplitude and resonance radius of Pluronic- or DMPC-coated microbubbles were found to depend very little on the concentrations. The resonance radius was around 65 μm at 38.8 kHz under all the experimental conditions investigated. The lifetime of the microbubbles was investigated simultaneously by measuring their temporal change in volume, and it was increased with Pluronic concentration. Remarkably, the oscillation amplitude of the bubble has an effect on the bubble lifetime. In other words, larger oscillation under the resonance condition accelerates the diffusion of the inner gas.

Wave velocities in articular cartilage measured by micro-Brillouin scattering technique

Micro-Brillouin scattering was used to measure gigahertz ultrasonic wave velocities in the articular cartilage of a bovine femur. Velocities propagating parallel to the surface of the subchondral bone were 3.36-3.83 × 10³m/s in a dry cartilage sample. Anisotropy measurements were also performed in a 10-μm-diameter local area of the cartilage matrix. A weak velocity anisotropy reflected characteristics of the layers. The velocity also depended on the water content. In the middle layer, the velocity in the dry sample was 3.58 × 10³m/s, whereas that for a fully wet sample was 2.04 × 10³m/s.

Noncontact Transportation of Planar Object in an Ultrasound Waveguide

This paper investigates acoustic levitation and noncontact transportation techniques for use with planar objects. An acoustic levitation system was developed which consists of a 1-mm-thick and 400-mm-long bending plate along with two bolt-clamped Langevin-type transducers (BLTs) that have stepped horns. A plane reflector was installed parallel to the vibrating plate to generate an ultrasound standing wave between the reflector and the plate. The sound pressure distribution in the ultrasound waveguide was calculated via finite-element analysis to investigate the effects of levitation of a planar object in the standing-wave field. A 1-mm-thick polystyrene plate was levitated along the nodal line of the acoustic standing wave in the waveguide. By controlling the driving phase difference between the two BLTs, the position at which flexural vibration occurs on the vibrating plate could be shifted along the length direction, and the trapped planar object could be moved by 9 mm along the same direction when the phase difference was varied from 0° to 360°.

Rapid Wave Velocity Measurement by Brillouin Scattering Using Coherent Phonons Induced by ScAlN Piezoelectric Thin-Film Transducer

It is difficult to perform 2-D imaging of elastic properties using the Brillouin scattering technique because the weak thermal phonon signal in the sample leads to low measurement accuracy and long measurement times. To improve the phonon signal, we artificially induced acoustic phonons using a ScAlN thin-film piezoelectric transducer, which has a giant piezoelectricity. The film was grown using RF magnetron sputtering of a ScAl alloy target on a silica glass bar sample. Using a microwave probe, the electric power applied to the film was 1 mW at 875 MHz. We obtained the enhancement of the Brillouin scattering signal in the silica glass bar sample due to the induced phonons. Compared with and without the induced phonons from the ScAlN film transducer, the peak intensity improved by nearly 3 orders of magnitude. This technique can significantly shorten the time required for the Brillouin scattering measurements.

Regional population differences of the brown planthopper (Nilaparvata lugens Stål) in Cambodia using genotyping-by-sequencing

The brown planthopper Nilaparvata lugens Stål (BPH) can be found year-round in tropical region and causes severe damage to rice. Although there has been documented BPH damage to rice crops in the past decade in Cambodia, the extent of this epidemic is poorly understood. Here, we examined the time variation of BPH population in the abundance of morphotypes in 13 main rice-producing provinces (86 sites) by aspirator method and in the Takeo Province (five sites) by yellow sticky trap method. At least three generations were observed during the 3-month collection period in the rainy growing season. Regarding the occurrence of BPH morphotypes, in July the macropterous adults were restricted to south Cambodia and in August all morphotypes, adults (macropterous and brachypterous) and nymphs, appeared in all sampling sites. To explain the difference of regional distribution, the genetic differentiation was analyzed in south and northwest Cambodia (three sites) by using single nucleotide polymorphisms (SNP) analysis via genotyping-by-sequencing (GBS) using next-generation sequencing. The 2455 SNPs obtained by GBS clarified the three sub-populations and they corresponded to the expected dissemination patterns. These results provide a clue to understand the differentiation and epidemic of BPH in Cambodia.

Control of hydroxyapatite film orientation by RF magnetron sputtering

Hydroxyapatite (HAp) is compatible with bone tissue and used as a bone prosthetic material especially for the implants coating. The c-axis of biological apatite (BAp) in bone is mainly oriented along the bone axis direction due to the mechanical stress produced in this direction. Then, the coating of implant with c-axis parallel oriented HAp thin film is expected to improve the healing speed. In this study, fabrication of oriented HAp thin films was performed by using a RF magnetron sputtering technique. The control of the HAp orientation in the film was achieved by changing the gas conditions, distance and angle between the target and substrate during sputtering.

Telomere length determined by the fluorescence in situ hybridisation distinguishes malignant and benign cells in cytological specimens

BACKGROUND

Telomeres are tandem repeats of TTAGGG at the end of eukaryotic chromosomes that play a key role in preventing chromosomal instability. The aim of the present study is to determine telomere length using fluorescence in situ hybridisation (FISH) on cytological specimens.

METHODS

Aspiration samples (n = 41) were smeared on glass slides and used for FISH.

RESULTS

Telomere signal intensity was significantly lower in positive cases (cases with malignancy, n = 25) as compared to negative cases (cases without malignancy, n = 16), and the same was observed for centromere intensity. The difference in DAPI intensity was not statistically significant. The ratio of telomere to centromere intensity did not show a significant difference between positive and negative cases. There was no statistical difference in the signal intensities of aspiration samples from ascites or pleural effusion (n = 23) and endoscopic ultrasound-guided FNA samples from the pancreas (n = 18).

CONCLUSIONS

The present study revealed that telomere length can be used as an indicator to distinguish malignant and benign cells in cytological specimens. This novel approach may help improve diagnosis for cancer patients.

Fast decomposition of two ultrasound longitudinal waves in cancellous bone using a phase rotation parameter for bone quality assessment: Simulation study

Ultrasound signals that pass through cancellous bone may be considered to consist of two longitudinal waves, which are called fast and slow waves. Accurate decomposition of these fast and slow waves is considered to be highly beneficial in determination of the characteristics of cancellous bone. In the present study, a fast decomposition method using a wave transfer function with a phase rotation parameter was applied to received signals that have passed through bovine bone specimens with various bone volume to total volume (BV/TV) ratios in a simulation study, where the elastic finite-difference time-domain method is used and the ultrasound wave propagated parallel to the bone axes. The proposed method succeeded to decompose both fast and slow waves accurately; the normalized residual intensity was less than -19.5 dB when the specimen thickness ranged from 4 to 7 mm and the BV/TV value ranged from 0.144 to 0.226. There was a strong relationship between the phase rotation value and the BV/TV value. The ratio of the peak envelope amplitude of the decomposed fast wave to that of the slow wave increased monotonically with increasing BV/TV ratio, indicating the high performance of the proposed method in estimation of the BV/TV value in cancellous bone.

On-chip ultrasonic manipulation of microparticles by using the flexural vibration of a glass substrate

As biotechnology develops, techniques for manipulating and separating small particles such as cells and DNA are required in the life sciences. This paper investigates on-chip manipulation of microparticles in small channels by using ultrasonic vibration. The chip consists of a rectangular glass substrate with a cross-shaped channel (cross-section: 2.0×2.0mm²) and four lead zirconate titanate transducers attached to the substrate's four corners. To efficiently generate the flexural vibration mode on the chip, we used finite element analysis to optimize the configurations of the glass substrate and transducers. Silicon carbide microparticles with an average diameter of 50μm were immersed in the channels, which were filled with ethanol. By applying an in-phase input voltage of 75V at 225kHz to the four transducers, a flexural vibration mode with a wavelength of 13mm was excited on the glass substrate, and this flexural vibration generated an acoustic standing wave in the channel. The particles could be trapped at the nodal lines of the standing wave. By controlling the driving phase difference between the two pairs of transducers, the vibrational distribution of the substrate could be moved along the channels so that the acoustic standing wave moved in the same direction. The trapped particles could be manipulated by the two-phase drive, and the transport direction could be switched at the junction of the channels orthogonally by changing the combination of the driving condition to four transducers.

[New methods for the evaluation of bone quality. Bone Quality Evaluation by QUS.]

The conventional ultrasonic bone densitometry systems(quantitative ultrasound:QUS)are now popular for the initial screening of osteoporosis. These systems can give us velocity(SOS)and broadband attenuation(BUA)of ultrasonic waves, which propagated in the heel. This paper describes the physical meaning of these parameters and introduces the idea of standardization, s-SOS and s-BUA. In addition, new QUS techniques for the further investigation of bone quality are also introduced. These techniques, two wave phenomenon and Axial Transmission(AT)can induce the individual properties of cortical and cancellous bones by the ultrasonic measurements.

Simulation study of axial ultrasonic wave propagation in heterogeneous bovine cortical bone

The effect of the heterogeneity of the long cortical bone is an important factor when applying the axial transmission technique. In this study, the axial longitudinal wave velocity distributions in specimens from the mid-shaft of a bovine femur were measured, in the MHz range. Bilinear interpolation and the piecewise cubic Hermite interpolating polynomial method were used to construct three-dimensional (3D) axial velocity models with a resolution of 40 μm. By assuming the uniaxial anisotropy of the bone and using the results of previous experimental studies [Yamato, Matsukawa, Yanagitani, Yamazaki, Mizukawa, and Nagano (2008b). Calcified Tissue Int. 82, 162-169; Nakatsuji, Yamamoto, Suga, Yanagitani, Matsukawa, Yamazaki, and Matsuyama (2011). Jpn. J. Appl. Phys. 50, 07HF18], the distributions of all elastic moduli were estimated to obtain a 3D heterogeneous bone model and a uniform model. In the heterogeneous model, moduli at the surface were smaller than those inside the model. The elastic finite-difference time-domain method was used to simulate axial ultrasonic wave propagation in these models. In the heterogeneous model, the wavefront of the first arriving signal (FAS) was dependent on the heterogeneity, and the FAS velocity depended on the measured position. These phenomena were not observed in the uniform model.

Acoustic Wave Velocities and Refractive Indices in an m-Plane GaN Single Crystal Plate and c-Axis Oriented ScAlN Films Measured by Brillouin Scattering Techniques

We have experimentally investigated wave velocities and refractive indices in bulk and film samples [a GaN single crystal plate and c-axis-oriented ScxAl(1-x)N (x = 0.00-0.63) films] by Brillouin scattering. All of the piezoelectrically unstiffened elastic constants and the ordinary refractive index of the GaN single crystal plate were determined from the reflection induced A (RIA) scattering geometry and the combination of 90R and 180° scattering geometries. The uncertainties of the measured wave velocities were approximately 0.17% (RIA) and 2.5% (combination technique). In addition, the longitudinal wave velocities of ScxAl(1-x)N films propagating in the normal direction were obtained by the combination technique. The maximum uncertainty was approximately 3.3%. The shear wave velocities and refractive indices of ScxAl(1-x)N films were also investigated by the 90R scattering geometry using velocities measured by high-overtone bulk acoustic resonators. The softening trends of the elasticity were obtained from the measured longitudinal and shear wave velocities, although there were large uncertainties in the Brillouin measurement system owing to thermal instability.

[Bone quantitative ultrasound]

The conventional ultrasonic bone densitometry system can give us information of bone as ultrasonic wave velocity and attenuation. However, the data reflect both structural and material properties of bone. In order to focus only on the bone matrix properties without the effect of bone structure, studies of microscopic Brillouin scattering technique are introduced. The wave velocity in a trabecula was anisotropic and depended on the position and structure of the cancellous bone. The glycation also affected on the wave velocities in bone. As a new bone quality, the piezoelectricity of bone is also discussed.

Two-dimensional noncontact transportation of small objects in air using flexural vibration of a plate

This paper investigates a two-dimensional ultrasonic manipulation technique for small objects in air. The ultrasonic levitation system consists of a rectangular vibrating plate with four ultrasonic transducers and a reflector. The configuration of the vibrator, the resonant frequency, and the positions of the four transducers with step horns were determined from finite element analysis such that an intense acoustic standing-wave field could be generated between the plates. A lattice flexural vibration mode with a wavelength of 28.3 mm was excited on the prototype plate at 24.6 kHz. Small objects could get trapped in air along the horizontal nodal plane of the standing wave. By controlling the driving phase difference between the transducers, trapped objects could be transported without contact in a two-dimensional plane. When the phase difference was changed from 0° to 720°, the distance moved by a small particle in the orthogonal direction was approximately 29 mm, which corresponds with the wavelength of the flexural vibration on the vibrating plate.

Signal of Interest Selection Standard for Ultrasonic Backscatter in Cancellous Bone Evaluation

The aim of this study was to examine the effect of the backscattered signal of interest (SOI) on ultrasonic cancellous bone evaluation. In vitro backscatter measurements were performed using 16 bovine cancellous bone specimens and six different transducers with central frequencies of 0.5, 1, 2.25, 3.5, 5 and 10 MHz. The SOI for signal analysis was selected by a rectangular window. The delay (T1) and duration (T2) of the time window were varied, and the apparent integrated backscatter (AIB) and its correlation to bone volume fraction (BV/TV) were calculated. The results indicate that in addition to affecting the measured value of AIB, the SOI influences the observed correlation between AIB and BV/TV. Strong positive correlations were observed for short T1 (0.5 MHz: ≤6 μs, 1 MHz: ≤3 μs, 2.25 and 3.5 MHz: ≤2 μs, 5 and 10 MHz: ≤1 μs). However, strong negative correlations were observed when T1 was long (0.5 MHz: >9 μs, 1 MHz: >7 μs, 2.25 and 3.5 MHz: >3 μs, 5 and 10 MHz: >2 μs). The T2 value, especially low values (≤3 μs), also influenced the correlation coefficients. Positive correlations were more commonly observed at lower frequencies (i.e., 0.5-1 MHz), whereas negative correlations were more common at higher frequencies (i.e., 2.25-10 MHz). An explicit standard for in vitro SOI selection and cancellous bone assessment was proposed for a broad frequency range (0.5-10 MHz). Current conflicting findings are explained, and constructive suggestions for ultrasonic backscatter cancellous bone evaluation are provided.

Conventional, Bayesian, and Modified Prony's methods for characterizing fast and slow waves in equine cancellous bone

Conventional, Bayesian, and the modified least-squares Prony's plus curve-fitting (MLSP + CF) methods were applied to data acquired using 1 MHz center frequency, broadband transducers on a single equine cancellous bone specimen that was systematically shortened from 11.8 mm down to 0.5 mm for a total of 24 sample thicknesses. Due to overlapping fast and slow waves, conventional analysis methods were restricted to data from sample thicknesses ranging from 11.8 mm to 6.0 mm. In contrast, Bayesian and MLSP + CF methods successfully separated fast and slow waves and provided reliable estimates of the ultrasonic properties of fast and slow waves for sample thicknesses ranging from 11.8 mm down to 3.5 mm. Comparisons of the three methods were carried out for phase velocity at the center frequency and the slope of the attenuation coefficient for the fast and slow waves. Good agreement among the three methods was also observed for average signal loss at the center frequency. The Bayesian and MLSP + CF approaches were able to separate the fast and slow waves and provide good estimates of the fast and slow wave properties even when the two wave modes overlapped in both time and frequency domains making conventional analysis methods unreliable.

Ultrasonic wave properties of human bone marrow in the femur and tibia

Ultrasonic wave properties of human bone marrow obtained in the femur and tibia were measured using an ultrasound pulse technique. The measured frequency range was 4-10 MHz, and the temperature range was 30 °C-40 °C. The sound velocity was 1410 m/s, and the attenuation coefficient was 4.4 dB/cm at 36 °C (10 MHz). These values decreased with temperature. Site dependence and individual differences in elderly human bone marrow were negligible. The slopes of the attenuation coefficient were estimated by a power law. The values of the exponent n were 2.0 (30 °C-38 °C) and 2.3 (40 °C).

Fast characterization of two ultrasound longitudinal waves in cancellous bone using an adaptive beamforming technique

The received signal in through-transmission ultrasound measurements of cancellous bone consists of two longitudinal waves, called the fast and slow waves. Analysis of these fast and slow waves may reveal characteristics of the cancellous bone that would be good indicators of osteoporosis. Because the two waves often overlap, decomposition of the received signal is an important problem in the characterization of bone quality. This study proposes a fast and accurate decomposition method based on the frequency domain interferometry imaging method with a modified wave transfer function that uses a phase rotation parameter. The proposed method accurately characterized the fast and slow waves in the experimental study, and the residual intensity, which was normalized with respect to the received signal intensity, was less than -20 dB over the bone specimen thickness range from 6 to 15 mm. In the simulation study, the residual intensity was less than -20 dB over the specimen thickness range from 3 to 8 mm. Decomposition of a single received signal takes only 5 s using a laptop personal computer with a single central processing unit. The proposed method has great potential to provide accurate and rapid measurements of indicators of osteoporosis in cancellous bone.

Fabrication of an optical lens array using ultraviolet light and ultrasonication

A technique to form an optical lens array using an ultraviolet (UV)-curable resin and ultrasound was investigated. A UV-curable gel film was formed on a glass plate having four lead zirconate titanate (PZT) transducers. Excitation of the transducers generated a lattice flexural vibration mode on the glass plate. The acoustic radiation force acted to deform the surface of the gel film, so that a lens array could be fabricated on the gel film. The lens array was exposed to UV light under ultrasonication to cure the UV-curable film. The quality factor of the transducer resonance was decreased upon curing of the resin film because the cured resin dampened the vibration of the plate. The acoustic characteristics of the UV-curable gel film were measured by using an ultrasound pulse technique at the MHz range. The sound speed of the gel increased from 987 to 1006 m/s (increase of 1.9%) as the UV exposure time increased. The attenuation coefficient also increased and the larger attenuation of the resin caused the lens array to have a lower quality factor.

Ultrasound radiation from a three-layer thermoacoustic transformation device

A thermophone is a thermoacoustic transducer, which generates sound via time-varying Joule heating of an electrically conductive layer, which leads to expansion and contraction of a small pocket of air near the surface of the film. In this work, a 10-μm-thick Ag-Pd conductive film was coupled with heat-insulating and heat-releasing layers to fabricate a three-layer thermophone for generating ultrasound. The heat-insulating layer was 47 μm thick, and was made of glass. The heat-releasing layer was 594 μm thick, and was made of 94% alumina. Because of the simple sound-generation mechanism, which does not require mechanical moving parts, the Ag-Pd conductive film on the glass substrate can produce ultrasound radiation with broadband frequency characteristics, where exiting commercial electrode materials were used. We also demonstrate that the measured directivity patterns are in good agreement with theoretical predictions, assuming a rectangular diaphragm with the same size as the metallic film.