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.

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.

Evaluation of skeletal muscle elasticity using color Doppler shear wave imaging.

PURPOSE: This study aimed to (1) assess the precision and reproducibility of color Doppler shear wave imaging (CD SWI) by comparing it with shear wave elastography (SWE) via elasticity phantom measurements, and (2) investigate the potential clinical applications of CD SWI in the upper limb muscles by assessing the reproducibility of skeletal muscle elasticity evaluations. METHODS: Four elastography phantoms of different stiffness (6.0-7.5 wt%) were used to assess the precision and reproducibility of CD SWI (compared with SWE) at depths. Typical upper limb muscles of 24 men were also assessed for this comparison. RESULTS: At superficial depths (0-2 cm), the phantom measurements obtained using CD SWI and SWE were similar at all levels of stiffness. Furthermore, both methods were highly reliable, with almost perfect intra- and inter-operator reliabilities. At greater depths (2-4 cm), measurements obtained using both methods were similar at all stiffness levels. Although standard deviations (SDs) of the phantom measurements obtained using both methods at lower stiffness were similar, those at higher stiffness were different. The SD of the CD SWI measurements was < 50% of that of the SWE measurements. However, both methods were highly reliable in the phantom test, with almost perfect intra- and inter-operator reliabilities. The intra- and inter-operator reliabilities of the shear wave velocity measurements for typical muscles of the upper limbs were also substantial in clinical settings. CONCLUSION: CD SWI is a valid method for measuring elasticity, with precision and reliability as high as those of SWE.

B-line Elastography Measurement of Lung Parenchymal Elasticity.

This paper proposes a method to determine the elasticity of the lung parenchyma from the B-line Doppler signal observed using continuous shear wave elastography, which uses a small vibrator placed on the tissue surface to propagate continuous shear waves with a vibration frequency of approximately 100 Hz. Since the B-line is generated by multiple reflections in fluid-storing alveoli near the lung surface, the ultrasonic multiple-reflection signal from the B-line is affected by the Doppler shift due to shear waves propagating in the lung parenchyma. When multiple B-lines are observed, the propagation velocity can be estimated by measuring the difference in propagation time between the B-lines. Therefore, continuous shear wave elastography can be used to determine the elasticity of the lung parenchyma by measuring the phase difference of shear wave between the B-lines. In this study, three elastic sponges (soft, medium, and hard) with embedded glass beads were used to simulate fluid-storing alveoli. Shear wave velocity measured using the proposed method was compared with that calculated using Young's modulus obtained from compression measurement. Using the proposed method, the measured shear wave velocities (mean ± S.D.) were 3.78 ± 0.23, 4.24 ± 0.12, and 5.06 ± 0.05 m/s for soft, medium, and hard sponges, respectively, which deviated by a maximum of 5.37% from the values calculated using the measured Young's moduli. The shear wave velocities of the sponge phantom were in a velocity range similar to the mean shear wave velocities of healthy and diseased lungs reported by magnetic resonance elastography (3.25 and 4.54 m/s, respectively). B-line elastography may enable emergency diagnoses of acute lung disease using portable ultrasonic echo devices.

Binary Pattern Color Doppler Shear Wave Elastography.

Some studies suggested a correlation between tissue elasticity and diseases, such as Adhesive Capsulitis (AC) of the shoulder. One category of method to measure elasticity is by utilizing Doppler imaging. This paper discusses color Doppler shear wave elastography methods and demonstrated an experiment with biological tissue mimicking phantom. A simulation with binary pattern color Doppler shear wave elastography shows that wavelength of a shear wave with suggested magnitude is equal to four multiple of pitch strip in a color flow image. However, the larger amplitude changes the duty ratio and frequency of the pattern. An experiment with biological tissue mimicking Polyvinyl Alcohol (PVA) phantoms has shown that the binary pattern color Doppler method has successfully recovered shear wave velocity map and calculate the elasticity.Clinical Relevance-The result of experiments presents a possibility of using the method for quantitatively access the stage of tissue stiffness related disease.

Relationship between shear elastic modulus and passive force of the human rectus femoris at multiple sites: a Thiel soft-embalmed cadaver study.

PURPOSE: Estimation of muscle passive force from elasticity using shear wave elastography (SWE) has been reported. However, the relationship between the elasticity and passive force of human muscles has not been elucidated. This study investigated the elastic modulus-passive force relationship in human skeletal muscles at multiple sites. METHODS: Four rectus femoris (RF) muscles were dissected from a human Thiel-embalmed cadaver. Calibration weights (0-600 g in 60-g increments) were applied to the distal tendon via a pulley system, and the shear elastic modulus as an index of elasticity was measured using SWE. The shear elastic modulus of the RF was measured at the proximal, central, and distal portions. RESULTS: The results demonstrated that the relationships between the elasticity in the longitudinal direction of the muscle and the passive force were nearly linear for all tested sites, with coefficients of determination ranging from 0.813 to 0.993. CONCLUSION: Shear wave elastography may be used as an indirect method to measure the changing passive force at any site within human muscles.

Application of the novel estimation method by shear wave elastography using vibrator to human skeletal muscle.

In recent years, non-invasive measurement of tissue stiffness (hardness) using ultrasound elastography has attracted considerable attention. It has been used to evaluate muscle stiffness in the fields of rehabilitation, sports, and orthopedics. However, ultrasonic diagnostic devices with elastography systems are expensive and clinical use of such devices has been limited. In this study, we proposed a novel estimation method for vibration-based shear wave elastography measurement of human skeletal muscle, then determined its reproducibility and reliability. The coefficient of variation and correlation coefficient were used to determine reproducibility and reliability of the method by measuring the shear wave velocities in konjac phantom gels and agar phantom gels, as well as skeletal muscle. The intra-day, day-to-day, and inter-operator reliabilities were good when measuring the shear wave velocities in phantom gels. The intra-day and day-to-day reliabilities were good when measuring the shear wave velocities in skeletal muscle. The findings confirmed adequate reproducibility and reliability of the novel estimation method for vibration-based shear wave elastography. Therefore, the proposed measurement method may be a useful tool for evaluation of muscle stiffness.

Observing Bubble Cavitation by Back-Propagation of Acoustic Emission Signals.

Temporal- and spatial-resolved observations of microbubble cavitation generated through high-intensity ultrasound irradiation are key in improving both the efficiency and efficacy of ultrasound-assisted drug delivery systems. A method of measuring bubble cavitation applying an image-reconstruction technique of back-propagation of an acoustic cavitation emission (ACE) signal is proposed. A high-intensity focused ultrasound wave (pump wave) irradiates the bubble synchronously using ultrasound recording equipment to acquire the timing of the RF signal, which is produced when the bubble radiates a secondary wave during bubble cavitation. The ACE signal source is reconstructed through ultrasound-wave back-propagation followed by amplitude deconvolution. The proposed method was applied to microbubbles of an ultrasound contrast agent by changing the sound pressure of the pump wave. The method reliability of the temporal resolution was verified by simulating the amplitude-modulated signal of the virtual sound source. The temporal transition of the ACE signal exhibited sub-microsecond-order fluctuations in the signal intensity. From the amplitude signal image and the instantaneous frequency image reconstruction of the proposed method, two different ACE phenomena were visualized. One is the periodic pattern by the beat signals from the harmonic and ultraharmonic component of nonlinear oscillation under low-intensity ultrasound conditions. The other is the nonperiodic temporal and spatial distributions of this irradiation under high-intensity ultrasound conditions.

Shear wave velocity measurement of upper trapezius muscle by color Doppler shear wave imaging.

PURPOSE: Skeletal muscle stiffness is thought to be the result of increased tissue hardness, but measurement accuracy has been dependent on operator technique. We have proposed a novel shear wave real-time imaging method (color Doppler shear wave imaging: CD SWI) with continuous shear waves excited from the tissue surface by a mechanical vibrator. METHODS: Using the method, shear wave velocity was measured for the upper trapezius muscle. Adaptive shear wave velocity measurement by means of quality estimation of shear wave wavefront was adopted. We recruited 23 male volunteers with no history of orthopedic disease and recorded shear wave propagation to assess the intra- and inter-observer reliability. For intra-observer reliability, one observer took two measurements separated by a time delay, and the intra-class correlation coefficient (ICC) was calculated (1,1). For inter-observer reliability, ICC (2,1) was calculated from both observers' measurements. RESULTS: Mean propagation speed was 3.75 ± 0.47 (first) and 3.71 ± 0.49 m/s (second) for Observer A (ICC (1,1) = 0.91 [95% CI 0.76-0.96]) and 3.80 ± 0.53 m/s for Observer B (ICC (2,1) = 0.83 [95% CI 0.56-0.94]). CONCLUSIONS: This result suggests that our technique is satisfactorily reliable and has potential for future application in various fields, such as evaluation of muscle condition or the effects of rehabilitation.

Shear Wave Imaging of Breast Tissue by Color Doppler Shear Wave Elastography.

Shear wave elastography is a distinctive method to access the viscoelastic characteristic of the soft tissue that is difficult to obtain by other imaging modalities. This paper proposes a novel shear wave elastography [color Doppler shear wave imaging (CD SWI)] for breast tissue. Continuous shear wave is produced by a small lightweight actuator, which is attached to the tissue surface. Shear wave wavefront that propagates in tissue is reconstructed as a binary pattern that consists of zero and the maximum flow velocities on color flow image (CFI). Neither any modifications of the ultrasound color flow imaging instrument nor a high frame rate ultrasound imaging instrument is required to obtain the shear wave wavefront map. However, two conditions of shear wave displacement amplitude and shear wave frequency are needed to obtain the map. However, these conditions are not severe restrictions in breast imaging. This is because the minimum displacement amplitude is [Formula: see text] for an ultrasonic wave frequency of 12 MHz and the shear wave frequency is available from several frequencies suited for breast imaging. Fourier analysis along time axis suppresses clutter noise in CFI. A directional filter extracts shear wave, which propagates in the forward direction. Several maps, such as shear wave phase, velocity, and propagation maps, are reconstructed by CD SWI. The accuracy of shear wave velocity measurement is evaluated for homogeneous agar gel phantom by comparing with the acoustic radiation force impulse method. The experimental results for breast tissue are shown for a shear wave frequency of 296.6 Hz.

A Color-Doppler Shear-Wave-Imaging Phase-reconstruction Method Using Four Color Flow Images.

This study investigates shear wave phase map reconstruction using a limited number of color flow images (CFIs) acquired with a color Doppler ultrasound imaging instrument. We propose an efficient reconstruction method to considerably reduce the number of CFIs required for reconstruction and compare this method with Fourier analysis-based color Doppler shear wave imaging. The proposed method uses a two-step phase reconstruction process, including an initial phase map derived from four CFIs using an advanced iterative algorithm of optical interferometry. The second step reduces phase artifacts in the initial phase map using an iterative correction procedure that cycles between the Fourier and inverse Fourier domains while imposing directional filtering and total variation regularization. We demonstrate the efficacy of this method using synthetic and experimental data of a breast phantom and human breast tissue. Our results show that the proposed method maintains image quality and reduces the number of CFIs required to four; previous methods have required at least 32 CFIs to achieve equivalent image quality. The proposed method is applicable to real-time shear wave elastography using a continuous shear wave produced by a mechanical vibrator.

Evaluation of Peripheral Blood Circulation Disorder in Scleroderma Patients Using an Optical Sensor with a Pressurization Mechanism.

Blood circulation function of peripheral blood vessels in skin dermis was evaluated employing an optical sensor with a pressurization mechanism using the blood outflow and reflow characteristics. The device contains a light source and an optical sensor. When applied to the skin surface, it first exerts the primary pressure (higher than the systolic blood pressure), causing an outflow of blood from the dermal peripheral blood vessels. After two heartbeats, the pressure is lowered (secondary pressure) and blood reflows into the peripheral blood vessels. Hemoglobin concentration, which changes during blood outflow and reflow, is derived from the received light intensity using the Beer-Lambert law. This method was evaluated in 26 healthy female volunteers and 26 female scleroderma patients. In order to evaluate the blood circulation function of the peripheral blood vessels of scleroderma patients, pressurization sequence which consists of primary pressure followed by secondary pressure was adopted. Blood reflow during the first heartbeat period after applying the secondary pressure of 40mmHg was (mean±SD) 0.059±0.05%mm for scleroderma patients and 0.173±0.104%mm for healthy volunteers. Blood reflow was significantly lower in scleroderma patients than in healthy volunteers (p<0.05). This result indicates that the information necessary for assessing blood circulation disorder of peripheral blood vessels in scleroderma patients is objectively obtained by the proposed method.

Shear Wave Wavefront Mapping Using Ultrasound Color Flow Imaging.

A wavefront reconstruction method for a continuous shear wave is proposed. The method uses ultrasound color flow imaging (CFI) to detect the shear wave's wavefront. When the shear wave vibration frequency satisfies the required frequency condition and the displacement amplitude satisfies the displacement amplitude condition, zero and maximum flow velocities appear at the shear wave vibration phases of zero and π rad, respectively. These specific flow velocities produce the shear wave's wavefront map in CFI. An important feature of this method is that the shear wave propagation is observed in real time without addition of extra functions to the ultrasound imaging system. The experiments are performed using a 6.5 MHz CFI system. The shear wave is excited by a multilayer piezoelectric actuator. In a phantom experiment, the shear wave velocities estimated using the proposed method and those estimated using a system based on displacement measurement show good agreement.

Characterization of skin dermis microcirculation in flow-mediated dilation using optical sensor with pressurization mechanism.

Blood flows out of microvessels in the dermis when pressure higher than arterial blood pressure is applied to the fingertip, and subsequently re-flows into the microcirculation when pressure is released. Both the blood outflow and the reflow characteristics of microcirculation under pressurization are associated with microvasculature, blood and blood pressure. This study describes a novel method of measuring blood inflow and outflow characteristics of dermis microcirculation. An optical sensor, which is furnished with a 571 nm wavelength light source and a photodetector, is pressed to the skin surface using a pressure higher than the human subject's systolic arterial pressure. Hemoglobin concentration by change of the blood flow amount is estimated by the Beer-Lambert law. This method is applied to the measurement of blood inflow and outflow characteristics of microcirculation caused by reactive hyperemia after ischemia with duration of 5 min. Among three parameters evaluated, the one relating to the amplitude of pulsation shows a close correlation with conventional plethysmography, while the other two show varying time responses. Our method provides a new and useful insight into pathophysiology in health and disease conditions and may help researchers better understand the underlying mechanisms of numerous microcirculation-influenced diseases and medical conditions.

Characterization of secondary ultrasonic waves radiated by two oscillating bubbles.

PURPOSE: A bubble oscillating under an ultrasonic wave produces an interference sound field with the incident ultrasonic wave, forming fringe patterns of trapped microbubbles. We discuss secondary ultrasonic waves radiated by two oscillating bubbles in the incident ultrasonic wave in terms of both theory and experimental conditions. METHODS: Two oscillating bubbles produce an inherent secondary wave field that varies with the distance between the two bubbles and the phases of these waves. Here we discuss the Bjerknes force derived for two bubbles and microbubble trapping around the bubbles. The experiments were carried out using microbubbles produced with an ultrasonic contrast agent (Levovist). RESULTS AND CONCLUSIONS: The microbubble-trapping pattern observed around the bubbles in the experiment closely agrees with the numerical simulation.