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The basic concept of distance measurement using the alternate transmission of two different codes based on the pulse-echo method has been used to obtain an extension of the measurable distance, in which the temporal resolution is not degraded in the one-code transmission. The reflected signals from the object are measured by two correlation signals. The received signal is correlated with each transmitted signal. The truncation and truncated interference noise of signals is generated in the cross-correlation function. Which is a part of signal components. The signal components are changed according to the transmit signal. In this paper, the SNRs of alternate transmission of different chirp signals is described and investigated. The highest SNR is achieved by the high bandwidth and long length of the transmitted signal. Different bandwidth of the chirp transmission is simulated. SNRs of the proposed method between the experiment and simulation is compare.

Previous studies have shown that shear wave elastography of liver tissue can be unstable due to factors such as uncertainties in the acoustic radiation force (ARF) irradiation due to the influence of tissues near the surface and the complexity of the liver’s structure and its physical properties. This study aims to verify the influence of near-surface tissues on ARF and the effect of tissue structure on shear wave propagation and shear wave velocity (SWV) evaluation using wave propagation simulations by the elastic finite-difference time domain method. It is found that the ARF becomes weakly focused on multiple locations due to refraction of longitudinal waves by near-surface tissues, and multiple shear waves of small amplitude are propagated. However, a macroscopic SWV assessment, as in clinical practice, reduces the influence of near-surface tissues because the microscopic assessment results are averaged over the near-surface tissues.

We attempted to visualize a single microbubble driven by acoustic radiation force using a combination of pulse inversion Doppler and plane wave imaging. Commercial microbubbles, Sonazoid® underwent ultrasound exposure with a center frequency of 5.2 MHz, a pulse repetition frequency of 4 kHz, and a negative peak sound pressure of 1.59 MPa. It succeeded in separately detecting individual microbubbles with high sensitivity. The disappearance of freely-translating microbubbles could be observed as a broadened spectrum of Doppler signal, i.e. a pseudo-Doppler effect. However, the trend was not apparent in the case of wall-colliding microbubbles.

We compared the evaluation accuracy of amplitude envelope statistics under the transmission and reception conditions of compounded plane wave imaging (CPWI) and focused beam imaging (FBI). In a basic study using a homogeneous phantom, we found that the amplitude gradient in the depth direction and the point spread function in the lateral direction spread in the FBI reduced the accuracy of evaluation in amplitude envelope statistics. On the other hand, CPWI showed a more stable evaluation than FBI because of the elimination of sound field characteristics. In CPWI, the multi-Rayleigh model discriminated signals from two types of scatterer with high accuracy in the evaluation using phantoms mimicking fatty liver. It was confirmed that the combination of CPWI and the multi-Rayleigh model is effective for detecting early fatty liver disease. The results show that CPWI is effective for improving the robustness of amplitude envelope statistics.

The aim of this study was to elucidate the frequency dependence of the speed of sound (SoS) and attenuation coefficients in phantoms with controlled attenuation properties (scatterer density, scatterer size, absorption control material) and rat livers.The frequency dependence of SoS and attenuation coefficients were evaluated with ultrasound (1-15 MHz) by observing multiple phantoms with different scatterer sizes, densities, and presence or absence of evaporated milk as absorbing media. Normal and fatty model rat livers were examined with the same protocol.The phantom results revealed that the scatterer density and SoS of the base media were the dominant factors causing the changes in SoS. Frequency dependence was not observed in SoS. Assessment of the attenuation coefficient showed that the frequency dependence was mainly affected by absorption attenuation when the scatterer was as small as a hepatocyte (i.e. ≤ 10 µm). Scattering attenuation was also observed to affect frequency dependence when the scatterer was as large as lipid droplets (i.e. ≤ 40 µm).Assuming a consistent size of the main scatterers in the evaluation medium, the frequency dependence of the SoS and attenuation coefficients may provide insight into the scatterer density and the contribution of absorption and scattering attenuation. Further studies in the higher frequency band (up to about 50 MHz) are expected to advance the clinical application of high-frequency ultrasound.

In contrast enhancement ultrasound (CEUS), the vasculature image can be formed from nonlinear echoes arising from microbubbles in a blood flow. The use of binary-coded pulse compression is promising for improving the contrast of CEUS images by suppressing background noise. However, the amplitudes of nonlinear echoes can be reduced, and sidelobes by nonlinear echoes can occur depending on the binary code. Optimal Golay codes with slight nonlinear-echo reduction and nonlinear sidelobe have been proposed. In this study, CEUS images obtained by optimal Golay pulse compression are evaluated through experiments using Sonazoid microbubbles flowing in a tissue-mimicking phantom.

This study investigates how the translational velocity of phospholipid-coated bubbles caused by acoustic radiation force depends on their size. The translations of bubbles with mean radii of 0.9–5 μm were experimentally evaluated at five ultrasound frequency conditions (3.5, 5, 7.5, 10, and 15 MHz). We compared experimental data with theoretical prediction using a viscoelastic interfacial rheological model and a model suitable for high amplitude oscillation. The results suggested that the translation of bubbles could be enhanced for a mean radius of 1–3 μm but echo intensity could not.

In medical ultrasound imaging using microbubbles (MBs), the nonlinear echoes from the MBs are used for contrast-specific image construction. Techniques such as pulse inversion, amplitude modulation, and the combined method (PIAM) are employed to increase nonlinear components in the echoes. In addition, employment of pulse compression using binary-coded ultrasound can potentially increase the components. In the case of the nonlinear echo, however, a nonlinear sidelobe occurs around the compressed pulse (correlation peak), and nonlinear components for PIAM in the correlation peak are reduced. The shape of the nonlinear sidelobe and the nonlinear-component reduction in the correlation peak can be estimated from the binary codes used. In this study, the optimal binary codes for PIAM are determined from all patterns of 10, 16, and 20 bit Golay codes. Then, the performance of PIAM with pulse compression using each code is evaluated via computer simulations and experiments using the SonoVue MBs.

Previous studies have shown that evaluation results of shear wave elastography were unstable due to factors such as liver structure and complexity of physical properties. The present study attempts to verify the influence of liver microstructure (fat droplets and fibrous tissue) on the shear wave and shear wave velocity (SWV) evaluation using a shear wave propagation simulation by the elastic finite-difference time-domain method. It was found that disruption of the shear wave causes variations in the SWV of the liver around fat droplets, and the SWV of the fibrous tissue depends on the shear wave propagation direction and the tissue shape. In a nonalcoholic steatohepatitis liver, which contains fat and fiber, the influences of these two tissues are synergistically reflected in the SWV evaluation.

In previous studies, the double-Nakagami (DN) model has been proposed for fatty liver assessment and applied to in vivo rat livers and clinical data sets. The healthy liver structure filter (HLSF) method, which extracts non-healthy areas using two DN parameters, has also been proposed. In this paper, we first verify the accuracy of the DN model and the HLSF method for acoustic fields at 15 and 5 MHz, which were reproduced using numerical simulation. We then apply the method to clinical data sets of livers observed using a frequency of 3 MHz and investigate the method’s clinical usefulness. A positive correlation ( r = 0.28 ) was found between the ratio of the non-healthy area and fat mass. Although the results were inferior to the results produced using 15 MHz ultrasound ( r = 0.96 ), we found that it was possible to detect the difference between a normal liver and a fatty liver even at a lower frequency.

Chronic liver disease requires careful follow-up during long-term treatment, and development of a quantitative diagnosis method for liver fibrosis based on an ultrasonic imaging system is highly desired. Texture analysis using a co-occurrence matrix was applied to both clinical and simulated ultrasonic images of fibrotic livers. A sequence of matrices was generated for pixel-pair distance, r, and texture feature contrast was chosen to examine the response to r in combination with statistical analysis of echo amplitude distribution using a multi-Rayleigh model. The contrast converged with a larger value and fluctuated more significantly in response to r as fibrosis progressed in both the clinical and simulated ultrasonic images. The convergent value rapidly increased at the early stage of fibrosis, and the fluctuation became larger at the advanced stage of fibrosis. Analysis using simulated ultrasonic images with a known fibrous tissue structure theoretically clarified the relationship between contrast behavior and fibrosis progression. It was revealed that contrast convergent value and contrast fluctuation provided information on the fibrous tissue structure, and they are expected to be used for quantitative diagnosis of the degree of liver fibrosis.

We have proposed an evaluation method for liver fibrosis using an ultrasound B-mode image. We proposed a multi-Rayleigh (MRA) distribution model to express a probability density function of ultrasound echo envelope obtained from a fibrotic liver tissue. The MRA model enabled us to estimate quantitative liver fibrosis parameters such as amount of fibrotic tissue and fibrosis progressive ratio, and to quantitatively visualize the fibrotic tissue in the B-mode image. In previous studies, we addressed several challenges to quantitatively and correctly evaluate liver fibrosis using the MRA model in clinical condition. In the present study, we integrated past achievements as the optimized MRA model and evaluated the clinical ultrasound B-mode image of fibrotic liver. Using the optimized MRA model, the change of estimated fibrotic tissue characteristics according to the liver fibrosis stage well reflected the tissue structural change caused by liver fibrosis. We concluded that the fibrotic tissue characteristics can be quantitatively and correctly estimated in clinical condition by using the optimized MRA model.

Measurement of ultrasonic propagation characteristics in cancellous bone is one of the diagnosis methods of osteoporosis. In the examination, ultrasonic transducers are typically brought into contact with heel sides through an ultrasonic gel to effectively propagate ultrasound. Non-contact measurement of the speed of sound (SOS) in a heel using airborne ultrasound which passed through the heel has been proposed to enable the easy-repeatable and low-cost examination. However, the accuracy of the proposed method hasn't been sufficient in the measurement of agar phantoms or actual heels. The SOS is estimated based on determination of the time of flight (TOF) and measurement of the propagation path of ultrasound. Therefore, TOF determination and path-length measurement in the proposed method are improved. Then, SOS measurement for the parallel-sides agar phantom is evaluated.

Micro dispense mechanism Recently, micro-droplet dispensation has been required in printed-electronics (PE) technology. Devices with micro dispensing mechanism are of key importance in achieving a higher performance with these products. In fact, it is very difficult for the conventional dispenser to squeeze highly viscous liquid with picoliter resolution. This paper describes the development of a dispensing mechanism comprising a dispensing device andXYstage, both driven by the piezo impulsive force. The dispensing device is mainly composed of a pipette and a taper needle that is driven by a piezoelectric element. When the needle passes through the pipette, a droplet of the liquid adheres to the needle-tip end. A micro droplet can be transcribed to a target surface by bringing the droplet at the needle-tip end in contact with the target surface. On the contrary, in theXYstage, the small tables on the V-shaped grooves can be driven by the impulsive force generated by the mass connected to the piezoelectric element. TheXstage is stacked on theYstage, which allows fine positioning in the plane. In the experiment, an array of a small amount of 0.2-picoliter droplets was successfully developed on the glass plate.

We have been studied about non-contact measurement of respiration and heart rates. In previous papers, the measurement system of small velocity using the M-sequence-modulated signal and phase difference of reflected signals from the target has been proposed. In this paper, we describe measurement of breathing and heartbeat in a standing position using the proposed method. Body-surface velocities by breathing and heartbeat could be observed respectively when the volunteer was breathing and holding the breath. In addition, measured velocity of breathing volunteer includes the component by heartbeat. It is considered that it has possibility to measure breathing and heartbeat concurrently.

To develop a quantitative diagnostic method for liver fibrosis using an ultrasound B-mode image, a probability imaging method of tissue characteristics based on a multi-Rayleigh model, which expresses a probability density function of echo signals from liver fibrosis, has been proposed. In this paper, an effect of non-speckle echo signals on tissue characteristics estimated from the multi-Rayleigh model was evaluated. Non-speckle signals were determined and removed using the modeling error of the multi-Rayleigh model. The correct tissue characteristics of fibrotic tissue could be estimated with the removal of non-speckle signals.

The pulse-echo method based on transmission of an ultrasonic pulse and time-of-flight determination of a reflected echo is one of the typical methods of ultrasonic distance measurement. To improve the SNR of the reflected echo, pulse compression using an M-sequence is employed in the pulseecho method. In the case of a moving object, however, the echo is modulated owing to the Doppler effect The Doppler-shifted M-sequence modulated signal cannot be correlated with the reference signal corresponding to the transmitted M-sequence modulated signal. Therefore, Doppler velocity estimation by spectrum-pattern analysis of a cyclic M-sequence modulated signal and cross correlations with Doppler-shifted reference signals corresponding to the estimated Doppler velocities has been proposed. Meanwhile, in the case of measurement using multiple transducers, the airborne acoustic image can be formed from multipath cross-correlation functions. Then, the position of the object can be determined from the airborne acoustic image. When different ultrasound are simultaneously transmitted, preferred-pair M-sequence codes are typically used for coding ultrasound to avoid the crosstalk. In this paper, the position and velocity of the moving object are measured by using two loudspeaker and three microphones. Then, the effect of interference of two M-sequence modulated signals are evaluated by comparison between simultaneous-transmission and non-simultaneous-transmission.

This brief proposes a frequency synchronization method for a full-digital self-oscillating pulsewidth modulation (PWM) signal generator. The self-oscillating PWM signal generator (PSG) generates a variable switching frequency, which results in poor drive performance for a three-phase power inverter or converter. The proposed frequency synchronization method utilizes an additional carrier signal, such as a triangular wave, to fix the switching frequency of a self-oscillating PSG. The switching frequency is synchronized by the triangular wave. As a test case, a switching frequency of 312.5 kHz is used for a performance evaluation of the proposed PSG with a sampling frequency of 12.5 MHz. A first-order noise-shaped output has been obtained. A high-precision PWM signal with low distortion and high resolution of the effective duty cycle has been achieved within the bandwidth. The proposed synchronized self-oscillating PSG is implemented in a three-phase brushless dc motor driver system to confirm the three-phase synchronization performance. Undesirable ripple current from asynchronous operation was not observed. The switching frequencies were synchronized among the three phases.

In M-sequence pulse compression for acoustic distance measurement, a continuous signal modulated by the cyclic binary code in an M-sequence is transmitted. Then, the received signal is correlated with one cycle of the transmitted code. The time of flight for the estimation of the propagation distance is determined from the peak appeared in the cross-correlation function when both codes match. The temporal resolution of the measurement and the maximum measurable distance are determined by the cycle length of the transmitted signal and in a trade-off relationship. Alternate transmission of different M-sequence codes and cross-correlations with each code can extend the measurable distance without degradation of the temporal resolution. However, truncation noise in each code and truncated interference noise between codes are generated around correlation peaks. The patterns of these noises are varied by the combination of codes. Therefore, contamination by these noise can be suppressed by selecting suitable codes.

Microdroplet dispensation is required in current systems and industrial equipment. However, dispensing microdroplets from high-viscosity liquids using dropon-demand inkjet technologies is difficult. Therefore, a needle-type dispenser comprising a thin needle and glass capillary containing the liquid to be dispensed has been developed for microdroplet dispensation. When the needle passes through the capillary, a droplet of the liquid adheres to the needle tip. A microdroplet can be transcribed by bringing the needle-tip droplet into contact with the target surface. The needle-type dispenser can dispense sub-pico-liter droplets with viscosities of several hundred pascalseconds at a throughput of a droplet per 1 s. When a microdroplet is dispensed, a gap between the needle tip and target surface may be formed. Droplet volumes depend on the dispensing gap, and unstable if the gap fluctuates. Thus, a contact-detection method for the needle-tip droplet and target surface is proposed where the needle is vibrated by a piezoelectric actuator using a leaf spring. The needle-vibration characteristics depend on conditions between the needletip droplet and target surface. Contact of the needletip droplet with the target surface can be detected by the needle-vibration characteristics. The dispensing gap can thus be kept constant to dispense precise droplet volumes. In this study, the needle-vibration characteristics of the fabricated mechanism were evaluated experimentally for needle diameters of 500 and 100 µm. The needle-vibration displacements decreased depending on the dispensing gap for liquids with viscosities of 0.1 to 100 Pa•s.

A microsurface measurement system that is composed of the microrobot with the indenter and a vision based navigation system is proposed for investigating hardness and stiffness of such microparts. Here the tiny robot with the electromagnetic legs and the piezo elements incorporates with an electromagnetic driven microforce generator. This force generator can provide small forces up to 17 mN with 50 µN resolutions and push down the microindenter to the surface. The displacement of the indenter head can be also measured by the Linear Valuable Differential Transformer (LVDT) on machine. Thus, this mechanism can generate the small force and monitor the depth behaviour of the indenter during whole dwell time. Since the overall size of this mechanism is small enough to implement on the piezo-driven microrobot, the tiny robot with the microindenter is capable tomove precisely step by step with 1 µm per step so that the microindenter could be penetrated anywhere on the sample surface. With the help of an image processing technique, the vision based coordination system with the local close-up view and the overall global view has been developed to identify the locations of small robot and the indenter precisely within ±3 µm accuracy over the working range. In the experimental results, several results that the indentation load-depth characteristics of the unhealthy human tooth are measured automatically at the specified point are discussed.

Because of a growing need for unconstrained medical monitoring for unobtrusively observing individuals in a living space, we have been studied about non-contact measurement of vital information such as respiration and heartbeat using airborne ultrasound. In previous study, the measurement system of small displacement using the M-sequence-modulated signal and tracking phase difference of reflected signals from the target has been proposed. The measurement of respiration and heartbeat of the target in a standing position using a pair of the loudspeaker and the microphone has also been performed. However, body position cannot be measured using a pair of the loudspeaker and the microphone because the system can measure the distance to the body only. In this paper, we describe a basic study of the measurement of body position, respiration, and heartbeat. In the system, using microphone array, body position was estimated by synthetic aperture processing. In addition, small body-surface velocity by respiration a...

A quantitative diagnostic method for liver fibrosis using ultrasound echo signals is highly required. A probability density function (PDF) of echo envelope from a normal liver can be approximated by a Rayleigh distribution; however, the PDF of echo envelope from liver fibrosis deviates from the Rayleigh distribution. To evaluate tissue characteristics in the ultrasound B-mode image, several amplitude distribution models have been proposed. We proposed a multi-Rayleigh distribution model and evaluation method of liver fibrosis using the multi-Rayleigh model. In this study, we evaluated the modeling accuracy of the multi-Rayleigh model and other amplitude distribution models using the KL divergence. From the evaluated results for the 120 clinical data, it was found that the multi-Rayleigh model with three components is more suitable model than other amplitude distribution models for approximating the PDF of echo envelope from the liver fibrosis.

Measurement and evaluation of ultrasonic propagation characteristics in cancellous bone is one of the diagnosis methods of osteoporosis. Non-contact measurement of propagation characteristics in a heel using airborne ultrasound which passed through the heel has been proposed. The pass-through ultrasound is extremely attenuated due to large reflections at boundaries between air and heel surfaces. In the proposed method, therefore, the signal-to-noise ratio of the pass-through ultrasound is greatly improved by pulse compression using an higher-order M-sequence. Furthermore, the pass-through ultrasound also inflects at the boundaries. Therefore, the direction of the ultrasonic beam varies depending on the shape of the heel. In this paper, a method for reception of the pass-through ultrasound by considering inflections at the boundaries is described.

Ultrasonic distance measurement for obstacles has been recently applied in automobiles. The pulse–echo method based on the transmission of an ultrasonic pulse and time-of-flight (TOF) determination of the reflected echo is one of the typical methods of ultrasonic distance measurement. Improvement of the signal-to-noise ratio (SNR) of the echo and the avoidance of crosstalk between ultrasonic sensors in the pulse–echo method are required in automotive measurement. The SNR of the reflected echo and the resolution of the TOF are improved by the employment of pulse compression using a maximum-length sequence (M-sequence), which is one of the binary pseudorandom sequences generated from a linear feedback shift register (LFSR). Crosstalk is avoided by using transmitted signals coded by different M-sequences generated from different LFSRs. In the case of lower-order M-sequences, however, the number of measurement channels corresponding to the pattern of the LFSR is not enough. In this paper, pulse compression using linear-frequency-modulated (LFM) signals coded by M-sequences has been proposed. The coding of LFM signals by the same M-sequence can produce different transmitted signals and increase the number of measurement channels. In the proposed method, however, the truncation noise in autocorrelation functions and the interference noise in cross-correlation functions degrade the SNRs of received echoes. Therefore, autocorrelation properties and cross-correlation properties in all patterns of combinations of coded LFM signals are evaluated.

Micro/nano positioning is one of important techniques to operate bio-cell and micro assembly. For realizing the precise positioning, the various piezo-driven stages have been already proposed and micro/nano scale resolution has been achieved. However, it is pointed out that the existing precision positioning tools are too large compared to operating area. Their devices are too difficult to combine other devices and use in tight environment like under microscope. In this paper, a precise positioning method with wire connected mechanism under microscope is proposed. The proposed positioning system is simply composed actuators including piezoelectric element and super extra-fine wires. By applying wire connected mechanism, the saving of larger work environment compared to traditional devices is hoped.

Real-time distance measurement of a moving object with high accuracy and high resolution using an ultrasonic wave is difficult due to the influence of the Doppler effect or the limit of the calculation cost of signal processing. An over-sampling signal processing method using a pair of LPM signals has been proposed for ultrasonic distance and velocity measurement of moving objects with high accuracy and high resolution. The proposed method consists of cross correlation by single-bit signal processing, high-resolution Doppler velocity estimation with wide measurement range and low-calculation-cost Doppler-shift compensation. The over-sampling cross-correlation function is obtained from cross correlation by single-bit signal processing with low calculation cost. The Doppler velocity and distance of the object are determined from the peak interval and peak form in the cross-correlation function by the proposed method of Doppler velocity estimation and Doppler-shift compensation. In this paper, the proposed method of Doppler-shift compensation is improved. Accuracy of the determined distance was improved from approximately within ±140 μm in the previous method to approximately within ±10 μm in computer simulations. Then, the proposed method of Doppler velocity estimation is evaluated. In computer simulations, accuracy of the determined Doppler velocity and distance were demonstrated within ±8.471 mm/s and ±13.87 μm. In experiments, Doppler velocities of the motorized stage could be determined within ±27.9 mm/s.

In recent years, electrical equipments, including their components, have seen a downsizing. Thus there is a growing need for micromanipulators for microscopic objects. Direct holding type micromanipulators have become popular. However, manipulating microscopic objects with direct holding type micromanipulators, there is a danger of damaging the objects. Manipulation using surface-tension involves holding the object by a droplet created on the tip of capillary. There is no direct contact between the capillary and the object. However, this way of manipulation does not support multiple degrees of freedom. Multi-needle type capillary is composed of several thin needles which are arranged cylindrically. These needles are used as hypothetical capillary. Such a multi-needle capillary can hold microscopic objects with the surface tension of droplet on the capillary tip. The multi-needle capillary tip can be reconfigured by a linear movement of each needle. Accordingly, the droplet on the capillary-tip is also reshaped, so that a microscopic object in contact with the capillary-tip droplet can be manipulated. In this paper, design and fabrication of multi-needle-type capillary is described.