This paper reviews the basic imaging methods available using ultrasonic diagnostic equipment, including the pulse-echo method, beamforming for improving image resolution, and harmonic imaging using the nonlinearity of ultrasonic waves. Further topics discussed include the use of the pulse Doppler method in blood flow measurement, and the differential diagnosis of benign and malignant tumor via the contrast echo method using microbubbles. Of particular relevance, the characteristic ultrasound image features used to inform the diagnosis of pneumonia severity, which is important in planning the treatment of COVID-19 patients, are described. Finally, a bird's eye view of future trends in ultrasonic diagnosis is provided.
Although the mechanisms involved remain unclear, several studies have reported that bone-conducted ultrasounds (BCUs) can be perceived even by those with profound sensorineural hearing impaired, who typically hardly sense sounds even with conventional hearing aids. We have identified both the psychological characteristics and the neurophysiological mechanisms underlying the perception of BCUs using psychophysical, electrophysiological, vibration measurements and computer simulations, and applied to a novel hearing aid for the profoundly hearing impaired. Also, mechanisms of perception and propagation of the BCU presented to distant parts of the body (neck, trunk, upper limb) were investigated.
A method of ultrasonic position and velocity measurements for a moving object by M-sequence pulse compression has been proposed. In the proposed method, the Doppler velocity is estimated from the peak in the autocorrelation function of the received signal, which includes cyclic M-sequences reflected from the object. Then, the received signal is correlated with the reference M-sequence expanded or compressed in accordance with the estimated Doppler velocity. The position is determined from the acoustic image formed from cross-correlation functions obtained in different propagation paths of ultrasound. In this paper, the simultaneous transmission of preferred-pair M-sequences is studied to improve the spatial resolution of the image while keeping the original frame rate of the proposed method. Experiments using the moving pole, two loudspeakers and three microphones are conducted to evaluate the estimated Doppler velocities and determined positions. In most situations, Doppler velocities can be accurately estimated when two different Doppler components are included in the received signal. In some situations, however, accurate Doppler velocities inevitably cannot be estimated due to the peak overlapping in the autocorrelation function. The accuracy of determined positions may degrade when the signal-to-noise ratio of the received signal is insufficient or Doppler velocities are not accurately estimated.
In this paper, we discuss methods of designing parametric speakers consisting of a small number of transducers. The developed parametric speaker unit includes peripheral acoustic structures, such as radial cones and a waveguide comprising a sonic crystal. The purpose of this study is to fabricate small parametric speakers that can be installed in various equipment. To achieve this purpose, it is essential to minimize the sizes and numbers of transducers. Parametric speakers must fulfill two goals: (1) high sound pressure levels of ultrasonic waves and (2) narrow directivities of ultrasonic waves. These two design goals are accomplished by two measures: (1) two close resonant frequencies and resonant mode control function and (2) an external adapter to obtain narrow directivities and high sound pressure. The first measure was achieved equipping the piezoelectric transducer with double-linked diaphragms and two radial cones. The second measure was embodied by the waveguide consisting of a sonic crystal, which was named the loop horn in this paper. Details of the design and experimental data of a four-transducer parametric speaker unit including the loop horn were presented.
In recent years, inactivation (sterilization) of bacteria using ultrasonic waves has attracted significant attention. However, the details of the inactivation mechanisms have not been elucidated. This study aims to clarify the inactivation mechanisms of bacteria and fungi by ultrasonic cavitation. Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) were used as the test bacteria, and Saccharomyces cerevisiae (S. cerevisiae) as the test fungi. Inactivation was attempted by ultrasonic irradiation at frequencies of 20 kHz to 4.4 MHz and an acoustic power density of 0.1 W/mL. Different frequency dependences of the inactivation were confirmed in E. coli, S. cerevisiae, and B. subtilis. The highest inactivation rate in E. coli was observed at 430 kHz. The effect of ultrasonic cavitation on E. coli was examined. We investigated the inactivation rate of E. coli when the sonochemical efficiency was kept constant at different frequencies (200, 430, and 950 kHz) by adjusting the acoustic power. The inactivation rates at different frequencies showed a similar time dependence. In contrast, B. subtilis spores were inactivated after increasing the power density. Based on these data, the mechanism of inactivation is discussed with a focus on cell characteristics.
We previously proposed a stable high-speed visualization measurement method that combines nonlinear harmonics with aerial ultrasonic wave source scanning. In this paper, a more efficient method is proposed to visualize a slit flaw in a metal plate. The results show that visualization of the propagation of ultrasonic waves was possible by wave source scanning. Harmonic propagation was also visible. The slit in the metal plate was visualized with the same accuracy as that of the previous laser probe scanning method.
Sand and small stones moving on the riverbed cause topographical changes such as local lowering and scouring. The measurement of particle size distribution of bed load is important to prevent river disasters, and a robust and simple particle sizer without using an electric power supply is required. In this study, a passive piezoelectric sensor for the measurement of the particle size distribution was developed and the continuous measurement for sequential impacts was analyzed. The sensor consists of an aluminum circular disc and an annular piezoelectric transducer. Naturally shaped gravel was employed as the bed load. When the gravel hits the surface of the sensor plate, resonance flexural vibration modes were excited on the sensor and electric power was generated through the piezoelectric effect. The size-discrimination parameters were defined by the spectral amplitudes of the resonance modes. The output signals of the sensor overlapped owing to the sequential impacts and the particle size distributions were estimated by time–frequency analysis.
Concave-type twin transducers with a center frequency of 1.93 MHz have been fabricated using polyvinylidene fluoride trifluoroethylene (P(VDF/TrFE)) resonators that have a transducer insertion loss of 100 dB (although this figure does not include the air absorption loss). A through-transmission acoustic imaging system was constructed using these twin (transmitting/receiving) P(VDF/TrFE) transducers. Burst waves composed of 50 cycles of sine-waves from a radio-frequency (RF) source were excited to approximately 600 Vpp by using a high-voltage power amplifier, and these high voltage burst waves were then input into the transmitting P(VDF/TrFE) transducer. Acquisition of the resulting small signal after it had passed through a sample object (a Rockwell 11229-12 logic integrated circuit) allowed the through-transmission image to be displayed on a personal computer monitor. The transverse resolution of this imaging system is approximately 0.5 mm. The results of this study demonstrate that these P(VDF/TrFE) piezoelectric films with their low acoustic impedances are applicable to through-transmission imaging in air in the MHz range.