Continuous Shear Wave Elastography for Liver Using Frame-to-Frame Equalization of Complex Amplitude

This study addresses a crucial necessity in the field of noninvasive liver fibrosis diagnosis by introducing the concept of continuous shear wave elastography (C-SWE), utilizing an external vibration source and color Doppler imaging. However, an application of C-SWE to assess liver elasticity, a deep region within the human body, arises an issue of signal instability in the obtained data. To tackle this challenge, this work proposes a method involving the acquisition of multiple frames of datasets, which are subsequently compressed. Furthermore, the proposed frame-to-frame equalization method compensates discrepancies in the initial phase that might exist among multiple-frame datasets, thereby significantly enhancing signal stability. The experimental validation of this approach encompasses both phantom tests and in vivo experiments. In the phantom tests, the proposed technique is validated through a comparison with the established shear wave elastography (SWE) technique. The results demonstrate a remarkable agreement, with an error in shear wave velocity of less than 4.2%. Additionally, the efficacy of the proposed method is confirmed through in vivo tests. As a result, the stabilization of observed shear waves using the frame-to-frame equalization technique exhibits promising potential for accurately assessing human liver elasticity. These findings collectively underscore the viability of C-SWE as a potential diagnostic instrument for liver fibrosis.

Examination of rapid adjustment system based on screen score obtained using continuous shear wave elastography

PURPOSE

Continuous shear wave elastography (C-SWE) can be expected to be applied to portable muscle elasticity diagnosis. To establish diagnostic technology, it will be necessary to improve measurement techniques and quantitative measurement accuracy.

METHODS

In this study, we investigated two screen scores: the quality index (Q-index), which determines whether the intensity of a power Doppler image is appropriate, and the shear wave propagation direction index (SWDI), which determines the uniformity of shear wave propagation.

RESULTS

First, we performed numerical simulations with white noise and found that the coefficient of variation of shear wave velocity estimation was less than 5% when the normalized Q-index was greater than 0.27. Furthermore, regarding the SWDI, we clarified the relationship between the standard deviation in shear wave propagation direction and the SWDI. Next, the relationship between the Q-index and coefficient of variation of estimated shear wave velocity was evaluated through experiments using a tissue-mimicking phantom. The results showed that there was a negative correlation between the Q-index and the coefficient of variation, and the fluctuation of the propagation velocity could be inferred from the Q-index. Finally, we showed the results of applying the screen scores to muscle relaxation monitoring and confirmed its usefulness in clinical applications.

CONCLUSION

By applying the screen scores, we showed improved stability in speed estimation in C-SWE, and demonstrated the possibility of clinical applicability.

Repetitive pulsed-wave ultrasound stimulation suppresses neural activity by modulating ambient GABA levels via effects on astrocytes

Ultrasound is highly biopermeable and can non-invasively penetrate deep into the brain. Stimulation with patterned low-intensity ultrasound can induce sustained inhibition of neural activity in humans and animals, with potential implications for research and therapeutics. Although mechanosensitive channels are involved, the cellular and molecular mechanisms underlying neuromodulation by ultrasound remain unknown. To investigate the mechanism of action of ultrasound stimulation, we studied the effects of two types of patterned ultrasound on synaptic transmission and neural network activity using whole-cell recordings in primary cultured hippocampal cells. Single-shot pulsed-wave (PW) or continuous-wave (CW) ultrasound had no effect on neural activity. By contrast, although repetitive CW stimulation also had no effect, repetitive PW stimulation persistently reduced spontaneous recurrent burst firing. This inhibitory effect was dependent on extrasynaptic-but not synaptic-GABAA receptors, and the effect was abolished under astrocyte-free conditions. Pharmacological activation of astrocytic TRPA1 channels mimicked the effects of ultrasound by increasing the tonic GABAA current induced by ambient GABA. Pharmacological blockade of TRPA1 channels abolished the inhibitory effect of ultrasound. These findings suggest that the repetitive PW low-intensity ultrasound used in our study does not have a direct effect on neural function but instead exerts its sustained neuromodulatory effect through modulation of ambient GABA levels via channels with characteristics of TRPA1, which is expressed in astrocytes.

Measurement of mechanical quality factors of polymers in flexural vibration for high-power ultrasonic application

A method for measuring the mechanical quality factor (Q factor) of materials in large-amplitude flexural vibrations was devised on the basis of the original definition of the Q factor. The Q factor, the ratio of the reactive energy to the dissipated energy, was calculated from the vibration velocity distribution. The bar thickness was selected considering the effect of the thickness on the estimation error. In the experimental setup, a 1-mm-thick polymer-based bar was used as a sample and fixed on the top of a longitudinal transducer. Using transducers of different lengths, flexural waves in the frequency range of 20-90kHz were generated on the bar. The vibration strain in the experiment reached 0.06%. According to the Bernoulli-Euler model, the reactive energy and dissipated energy were estimated from the vertical velocity distribution on the bar, and the Q factors were measured as the driving frequency and strain were varied. The experimental results showed that the Q factors decrease as the driving frequencies and strains increase. At a frequency of 28.30kHz, the Q factor of poly(phenylene sulfide) (PPS) reached approximately 460 when the strain was smaller than 0.005%. PPS exhibited a much higher Q factor than the other tested polymers, which implies that it is a potentially applicable material as the elastomer for high-power ultrasonic devices.

Ultrasonic motors with polymer-based vibrators

With their characteristics of low density and elastic moduli, polymers are promising materials for making ultrasonic motors (USMs) with high energy density. Although it has been believed for a long time that polymers are too lossy to be applied to high-amplitude vibrators, there are several new polymers that exhibit excellent vibration characteristics. First, we measure the damping coefficients of some functional polymers to explore the applicability of polymers as vibrators for USMs. Second, to investigate the vibration characteristics, we fabricate bimorph vibrators using several kinds of polymers that have low attenuation. Third, a bending mode USM is fabricated with a polymer rod and four piezoelectric plates bonded on the rod as a typical example of a USM. Through an experimental investigation of the motor performance, it was found that the polymer-based USMs exhibited higher rotation velocity than the aluminum-based USM under a light preload, although the maximum torque of the polymer-based USMs was smaller than the aluminum-based USM. Among the tested polymers, polyphenylenesulfide was a prospective material for USMs under light preloads because of the high amplitude and lightweight of polyphenylenesulfide.