Wave Speed Measurements Research Articles

Acoustic Structure Quantification Versus Point Shear Wave Speed Measurement for the Assessment of Liver Fibrosis in Viral Hepatitis B

This study was conducted to evaluate the value of acoustic structure quantification (ASQ) technology versus that of point shear wave speed measurement (PSWSM) imaging technology for the assessment of liver fibrosis stage. A total of 104 patients with chronic hepatitis B (CHB) and 30 healthy control patients underwent ASQ and PSWSM examinations. Seven quantitative parameters were obtained from ASQ, and a principal component analysis was used to establish the integrative indicators. A quantitative parameter, known as the shear wave speed (SWS, m/s), was obtained from the PSWSM. The METAVIR scores for the assessment of pathologic liver fibrosis were used as a benchmark. Liver fibrosis stages exhibited a good correlation with the integrative indicators and SWS (r = 0.682, p < 0.001; r = 0.651, p < 0.001). The areas under the receiver operating characteristic curves for ASQ and PSWSM were 0.705 and 0.854 for mild liver fibrosis (F ≥ 1, p = 0.045), 0.813 and 0.743 for significant liver fibrosis (F ≥ 2, p = 0.115), 0.839 and 0.857 for severe liver fibrosis (F ≥ 3, p = 0.417) and 0.874 and 0.971 for liver cirrhosis (F = 4, p = 0.016), respectively. In conclusion, both ASQ and PSWSM were promising ultrasonic methods for assessing liver fibrosis in patients with CHB; however, PSWSM was more valuable for identifying mild liver fibrosis (F ≥ 1) and cirrhosis (F = 4) than ASQ, and the combination of PSWSM and ASQ improved the accuracy of diagnosing severe liver fibrosis (F ≥ 3).

Finite element analysis of lung ultrasound surface wave elastography

Interstitial lung disease manifested as fibrotic and stiffened lung tissue, resulting in symptoms such as dyspnea and may lead to respiratory failure. We recently developed a lung ultrasound surface wave elastography for evaluating the elastic properties of superficial lung tissue. In this abstract, we present a finite element analysis to investigate the effects of pleural effusion on the shear wave propagation of superficial lung tissue. The muscle, pleural effusion, and lung tissue were simulated by a 2D planar model of an infinite elastic medium with densities for different materials. A nearly incompressible, linear elastic model was used to model muscle, pleural effusion and lung. The model was excited using a line source on the muscle surface. Harmonic excitations were performed at 100, 150 and 200 Hz with duration of 0.1 s. The boundaries of lung and muscle were attached to an infinite. The mesh of muscle, pleural effusion, and lung were constructed using linear quadrilateral elements. The infinite region was meshed by infinite elements (type CINPE4). The dynamic responses of the tissue model to the excitations were solved by the ABAQUS explicit dynamic solver with automatic step size control. Insignificant difference in shear wave speeds of lung tissue at different excitation frequencies was found in both simulations with and without taking into account the pleural effusion, indicating that pleural effusion does not affect the measurements of shear wave speeds in ultrasound elastography.Interstitial lung disease manifested as fibrotic and stiffened lung tissue, resulting in symptoms such as dyspnea and may lead to respiratory failure. We recently developed a lung ultrasound surface wave elastography for evaluating the elastic properties of superficial lung tissue. In this abstract, we present a finite element analysis to investigate the effects of pleural effusion on the shear wave propagation of superficial lung tissue. The muscle, pleural effusion, and lung tissue were simulated by a 2D planar model of an infinite elastic medium with densities for different materials. A nearly incompressible, linear elastic model was used to model muscle, pleural effusion and lung. The model was excited using a line source on the muscle surface. Harmonic excitations were performed at 100, 150 and 200 Hz with duration of 0.1 s. The boundaries of lung and muscle were attached to an infinite. The mesh of muscle, pleural effusion, and lung were constructed using linear quadrilateral elements. The infinite ...

Pleural fluid may pose no measurable effect on lung stiffness in lung ultrasound surface wave elastography

Lung ultrasound surface wave elastography (LUSWE) was developed as a non-invasive tool for assessing pulmonary fibrosis. In this research, the effect of the fleural fluid on surface wave speed measurement of the lung is studied. Low-cost sponges [J. Ultrasound Med. 2017; 36, 2133], as good lung phantoms, were used in this study. The ultrasound transmission gel was used to simulate the pleural fluid. A harmonic vibration was generated at sponge surfaces using a shaker at 100, 150, and 200 Hz. The sponge surface wave speeds were measured with a 6 MHz ultrasound probe for both with and without a thin layer gel. The ultrasound features of A and B-lines were clearly observed in every sponge model in our experiment. The surface wave speeds for the sponges with the gel were indistinguishable from those without the gel for each frequency. The surface wave speeds were faster at higher excitation frequencies which is consistent with our patient study results. It was conclude that the pleural fluid may not affect the lung surface wave speed measurement based upon our lung phantom sponge models.

A deep neural network method for analyzing lung density using lung ultrasound surface wave elastography

Lung density is directly associated with lung pathology. Computed Tomography (CT) evaluates lung pathology using the Hounsfield unit (HU) but not directly the lung density. We recently developed a lung ultrasound surface wave elastography (LUSWE) technique for measuring the surface wave speed of superficial lung tissue. The objective of this study is to analyze lung density of superficial lung tissue using deep neural network (DNN) and wave speed measurements obtained from LUSWE. The synthetic training dataset (7,88,000 in total) in terms of wave speeds of superficial lung tissue at different excitation frequencies from LUSWE, viscoelasticity and density of lung tissue was used to train the DNN. DNN is composed of 3 hidden layers of 1024 neurons and trained for 10 epochs with a batch size of 4096 and a learning rate of 0.001 with Adam optimizer. Test dataset in terms of wave speeds at different excitation frequencies (100, 150, and 200 Hz) as well as elasticity was used to predict the lung density and evaluate its accuracy. The obtained results showed that predictions matched well with test dataset (validation accuracy is 0.997). This method may be useful to analyze lung density based on the LUSWE measurements.

High frequency compressional wave speed and attenuation measurements in water-saturated granular media with unimodal and bimodal grain size distributions.

Compressional wave speed and attenuation were measured for water-saturated granular media employing five kinds of glass beads having unimodal and bimodal grain size distributions. Glass beads with grain sizes ranging from 250 to 850 μm were used for the acoustic measurements at a frequency range from 350 kHz to 1.1 MHz, which includes the transition range where scattering and non-scattering losses co-exist. The compressional wave speed and attenuation data are presented as a function of frequency and grain size distribution. The compressional wave speed and attenuation data show a variety of frequency dependencies for varying grain size distribution. The observed acoustic properties are investigated for the volume ratio of larger and smaller sized grains in the mixed bimodal media. Also, the measured results are compared with the empirical multiple scattering formula as a function of Rayleigh parameter kd (product of wavenumber in the water k and mean grain diameter of the glass beads d) using weighted mean grain size. The measured results are also discussed, focusing on the geophysical difference between unimodal and bimodal mixed grains.

Measurement of pressure wave speed in stainless-steel pipe generated by water hammer

This paper aims to demonstrate a measurement method of pressure wave speed in stainless-steel pipe filled with water caused by water hammer phenomenon. The pressure wave is generated using a self-developed drop impact testing equipment. An impactor is dropped to collide a buffer which then induces the water hammer phenomenon. The generated pressure and its propagation speed in the water are carefully measured here. Pressure measurement is conducted by a pressure transducer, while pressure wave speed is measured by two methods, which utilize peak time of the pressure recorded by pressure transducer and peak time of strains recorded by two strain gages positioned in a different location. These strain gages are oriented to the circumferential direction of the pipe. Measurement result shows that at 1.5 m height, impact pressure of between 0.86 to 1.16 MPa and wave velocity of 1250 m/s were obtained. From the experimental results, the characteristic of pressure wave in the water was able to be observed.

Detection of Changes in Cervical Softness Using Shear Wave Speed in Early versus Late Pregnancy: An in Vivo Cross-Sectional Study

The aim of this study was to assess the ability of shear wave elasticity imaging (SWEI) to detect changes in cervical softness between early and late pregnancy. Using a cross-sectional study design, shear wave speed (SWS) measurements were obtained from women in the first trimester (5–14 wk of gestation) and compared with estimates from a previous study of women at term (37–41 wk). Two sets of five SWS measurements were made using commercial SWEI applications on an ultrasound system equipped with a prototype catheter transducer (128 elements, 3-mm diameter, 14-mm aperture). Average SWS estimates were 4.42 ± 0.32 m/s (n = 12) for the first trimester and 2.13 ± 0.66 m/s (n = 18) for the third trimester (p < 0.0001). The area under the curve was 0.95 (95% confidence interval: 0.82–0.99) with a sensitivity and specificity of 83%. SWS estimates indicated that the third-trimester cervix is significantly softer than the first-trimester cervix. SWEI methods may be promising for assessing changes in cervical softness.

Evaluating the Benefit of Elevated Acoustic Output in Harmonic Motion Estimation in Ultrasonic Shear Wave Elasticity Imaging

Harmonic imaging techniques have been applied in ultrasonic elasticity imaging to obtain higher-quality tissue motion tracking data. However, harmonic tracking can be signal-to-noise ratio and penetration depth limited during clinical imaging, resulting in decreased yield of successful shear wave speed measurements. A logical approach is to increase the source pressure, but the in situ pressures used in diagnostic ultrasound have been subject to a de facto upper limit based on the Food and Drug Administration guideline for the mechanical index (MI <1.9). A recent American Institute of Ultrasound in Medicine report concluded that an in situ MI up to 4.0 could be warranted without concern for increased risk of cavitation in non-fetal tissues without gas bodies if there were a concurrent clinical benefit. This work evaluates the impact of using an elevated MI in harmonic motion tracking for hepatic shear wave elasticity imaging. The studies indicate that high-MI harmonic tracking increased shear wave speed estimation yield by 27% at a focal depth of 5 cm, with larger yield increase in more difficult-to-image patients. High-MI tracking improved harmonic tracking data quality by increasing the signal-to-noise ratio and decreasing jitter in the tissue motion data. We conclude that there is clinical benefit to use of elevated acoustic output in shear wave tracking, particularly in difficult-to-image patients.

Near field effect on elasticity measurement for cartilage-bone structure using Lamb wave method

BackgroundCartilage elasticity changes with cartilage degeneration. Hence, cartilage elasticity detection might be an alternative to traditional imaging methods for the early diagnosis of osteoarthritis. Based on the wave propagation measurement, Shear wave elastography (SWE) become an emerging non-invasive elasticity detection method. The wave propagation model, which is affected by tissue shapes, is crucial for elasticity estimating in SWE. However, wave propagation model for cartilage was unclear.MethodsThis study aimed to establish a wave propagation model for the cartilage-bone structure. We fabricated a cartilage-bone structure, and studied the elasticity measurement and wave propagation by experimental and numerical Lamb wave method (LWM).ResultsResults indicated the wave propagation model satisfied the lamb wave theory for two-layered structure. Moreover, a near field region, which affects wave speed measurements and whose occurrence can be prevented if the wave frequency is larger than one critical frequency, was observed.ConclusionOur findings would provide a theoretical foundation for further application of LWM in elasticity measurement of cartilage in vivo. It can help the application of LWM to the diagnosis of osteoarthritis.

Ultrasound measurement of texture in bulk polycrystalline materials

Manufacturing of metal components often results in significant texture, that is, to say, preferred orientations of their polycrystals. Since each crystal can be strongly anisotropic, this can give the component orientation-dependent material properties, affecting stiffness, thermal expansion, strength, and fatigue and creep resistance. So, it is important to be able to measure texture, especially for high-value safety-critical components. Typically, the Orientation Distribution Function (ODF) of the crystals can be measured on exposed surfaces using EBSD, or in thin samples using neutron diffraction. But both are expensive, and until recently there has not been a means to measure ODFs internally in bulk materials. However, the authors have recently developed a method to determine internal texture from measurements of wave speeds at selected angles through the volume of the material. This is based on a convolution of wave speeds in a single crystal with the ODF, giving the resultant polycrystal wave speed angular function. The principles of the method have been established and validated for single phase hexagonal and cubic materials. Ongoing work is investigating the use of multiple wave modes (shear and compressional) to identify further information; the extraction of volume fraction and texture of two-phase materials; and the pursuit of further refinement of the texture results by improved knowledge of the single crystal properties.

An application of Bayesian inference techniques to compare three competing sandy sediment models

Many competing geoacoustic models exist to represent sandy sediments. In this work, Bayesian inference is employed to compare the sensitivity of the physical input parameters of three competing models: the viscous grain shearing model of Buckingham, the Biot-Stoll model, and the extended Biot model of Chotiros, using previously taken wave speed and attenuation laboratory measurements. Bayesian model selection techniques are then employed to assess the degree to which the predictions of these models can be used to explain the observed data. Since all three geoacoustic models require a large number of input parameters and many of these input parameters are difficult to measure, a main goal of this work is to use Bayesian techniques to determine which parameters can be resolved via inversion and what kinds of data are required for parameter resolution. [Work supported by ONR, Ocean Acoustics.]

Thee-Dimensional Single-Track-Location Shear Wave Elasticity Imaging.

Conventional multiple-track-location shear wave elasticity imaging (MTL-SWEI) is a powerful tool for noninvasively estimating tissue elasticity. The resolution and noise levels of MTL-SWEI systems, however, are limited by ultrasound speckle. Single-track-location SWEI (STL-SWEI) is a novel variant which fixes the position of the tracking beam and modulates the push location to effectively cancel out the effects of speckle-induced bias. We present here a 3-D STL-SWEI system, which provides full suppression of lateral and elevation speckle bias for high-resolution volumetric elasticity imaging, and requires no spatial smoothing to make accurate measurements of shear wave speed. We demonstrate and analyze the system's performance in homogeneous and layered elasticity phantoms.

Influence of Tissue Microstructure on Shear Wave Speed Measurements in Plane Shear Wave Elastography: A Computational Study in Lossless Fibrotic Liver Media.

Shear wave elastography (SWE) has been used to measure viscoelastic properties for characterization of fibrotic livers. In this technique, external mechanical vibrations or acoustic radiation forces are first transmitted to the tissue being imaged to induce shear waves. Ultrasonically measured displacement/velocity is then utilized to obtain elastographic measurements related to shear wave propagation. Using an open-source wave simulator, k-Wave, we conducted a case study of the relationship between plane shear wave measurements and the microstructure of fibrotic liver tissues. Particularly, three different virtual tissue models (i.e., a histology-based model, a statistics-based model, and a simple inclusion model) were used to represent underlying microstructures of fibrotic liver tissues. We found underlying microstructures affected the estimated mean group shear wave speed (SWS) under the plane shear wave assumption by as much as 56%. Also, the elastic shear wave scattering resulted in frequency-dependent attenuation coefficients and introduced changes in the estimated group SWS. Similarly, the slope of group SWS changes with respect to the excitation frequency differed as much as 78% among three models investigated. This new finding may motivate further studies examining how elastic scattering may contribute to frequency-dependent shear wave dispersion and attenuation in biological tissues.

Ultrasound-Based Shear Wave Elastography in the Assessment of Patients with Diabetic Kidney Disease

In previous studies of acoustic radiation force impulse (ARFI) elastography, using Virtual Touch tissue quantification (VTQ) (Siemens Acuson S2000), it was reported that the measurement of renal shear wave speed in patients with chronic kidney disease (CKD) is not influenced exclusively by renal fibrosis. The purpose of the present study was to analyze the role of VTQ in patients with diabetic kidney disease, considered the main cause of CKD. The study group included 164 patients: 80 patients with diabetic kidney disease (DKD) and 84 without renal disease or diabetes mellitus. In each subject in lateral decubitus, five valid VTQ measurements were performed in each kidney and a median value was calculated, the result being expressed in meters/second. The following means of the median values were obtained In DKD patients, the means of the median values were for VTQ right kidney, 2.21 ± 0.71 m/s, and for VTQ left kidney, 2.13 ± 0.72 m/s, whereas in the normal controls statistically significant higher values were obtained: 2.58 ± 0.78 m/s for VTQ right kidney (p = 0.0017) and 2.46 ± 0.81 m/s for VTQ left kidney (p = 0.006). Patients with an estimated glomerular filtration rate (eGFR) >60 mL/min (DKD stages 1 and 2 together with normal controls) had a significantly higher kidney shear wave speed compared with patients with an eGFR <60 mL/min (2.53 m/s vs. 2.09 m/s, p < 0.05). In the DKD group, there was a significant correlation between eGFR and VTQ levels for the right kidney (r = 0.28, p = 0.04). There was no correlation of VTQ values with proteinuria level, stage of diabetic retinopathy or glycated hemoglobin. Our study indicates that shear wave speed values in patients with diabetic kidney disease and eGFRs <60 mL/min are significantly lower compared with those of patients with eGFRs >60 mL/min (either normal controls or diabetic patients with DKD stages 1 and 2), and values decrease with the decrease in eGFR. However, proteinuria, diabetic retinopathy and glycated hemoglobin have no influence on VTQ.

Quality Measurement of Two-dimensional Shear Wave Speed Imaging for Breast Lesions: the Associated Factors and the Impact to Diagnostic Performance

This study aimed to identify the associated factors for quality measurement (QM) of shear wave speed (SWS) imaging and to validate the additional value of QM in the diagnosis of breast lesions. From September 2014 to February 2015, conventional ultrasound and SWS imaging were performed in 338 women with 361 breast lesions. Binary logistic regression was used to identify associated factors for QM. Sensitivity, specificity and the area under receiver operating characteristic (ROC) curve (AUC) among maximum SWS (SWSmax), QM and SWSmax plus QM (SWSmax+QM) were compared to validate additional value of QM. Pathology confirmed 263 (72.9%) benign lesions and 98 (27.1%) malignancies. Maximum depth (Odds ratio [OR]: 1.398) and posterior features (OR: 1.206) were identified as independent associated factors for QM. Compared with SWSmax and QM, the sensitivity of SWSmax+QM increased from 67.3%, 64.3% to 83.7% whereas the specificity decreased from 90.5%, 72.6% to 65.4% (all P < 0.05). SWSmax had the highest AUC in comparison with QM and SWSmax+QM (0.849 vs. 0.685 vs. 0.745; P < 0.05). QM for breast lesions is associated with maximum depth and posterior features. Adding QM to SWSmax is useful for breast cancer screening and SWSmax alone is useful for breast cancer differentiation.

Large dataset test of Birch's law for sound propagation at high pressure

Birch's law, prescribing a linear dependence of elastic wave speed on the density in a given material, is an important tool in understanding the composition and thermodynamic conditions of the planetary interior. However, data from direct measurements of elastic wave speed usually have too much of scatter to permit a precise test of this law. Here, we use data from experimental measurements as well as ab initio density-functional-theory based calculations existing in the literature, supplemented by our own data of the latter type for elemental solids, for such a test. Using many such datasets, we show that, although Birch's law is satisfied fairly well in all the cases, the product of elastic wave speed and one-third power of density satisfies linear dependence on density consistently and more accurately than the speed alone. This opens the possibility of more reliable extrapolation of low density velocity data to the higher densities—the primary application of Birch's law.

Noninvasive measurement of wave speed of porcine cornea in ex vivo porcine eyes for various intraocular pressures

The objective of this study was to extend an ultrasound surface wave elastography (USWE) technique for noninvasive measurement of ocular tissue elastic properties. In particular, we aim to establish the relationship between the wave speed of cornea and the intraocular pressure (IOP). Normal ranges of IOP are between 12 and 22mmHg. Ex vivo porcine eye balls were used in this research. The porcine eye ball was supported by the gelatin phantom in a testing container. Some water was pour into the container for the ultrasound measurement. A local harmonic vibration was generated on the side of the eye ball. An ultrasound probe was used to measure the wave propagation in the cornea noninvasively. A 25 gauge butterfly needle was inserted into the vitreous humor of the eye ball under the ultrasound imaging guidance. The needle was connected to a syringe. The IOP was obtained by the water height difference between the water level in the syringe and the water level in the testing container. The IOP was adjusted between 5mmHg and 30mmHg with a 5mmHg interval. The wave speed was measured at each IOP for three frequencies of 100, 150 and 200Hz. Finite element method (FEM) was used to simulate the wave propagation in the corneal according to our experimental setup. A linear viscoelastic FEM model was used to compare the experimental data. Both the experiments and the FEM analyses showed that the wave speed of cornea increased with IOP.

Effective Media for Transversely Isotropic Models Based on Homogenization Theory: With Applications to Borehole Sonic Logs

Sonic log records, including measurements of wave speeds in boreholes, provide critical input to the geological, geophysical, and petrophysical studies of a region under exploration. 1D background models are routinely built based on sonic log records for applications such as seismic imaging of hydrocarbon reservoirs and microseismic source inversions. Smoothing or ‘upscaling’ techniques are required to produce models in coarser scales than the very fine layers in the raw log data. In this paper, we follow the recently popular homogenization theory, derive its application to the special case of 1D TI models for both P-SV and SH waves, and show that it is consistent with the Backus averaging technique commonly used to upscale 1D fine-layered models. We examine a study case of sonic log data from a well in the Horn River Basin in northeastern British Columbia, a region known for its tight shale-gas deposit. We demonstrate the computational accuracy and efficiency gained by proper upscaling procedures for spectral-element simulations of seismic wave propagation, and discuss the effect of control parameters on wavefield recovery.

Measurement of texture in polycrystalline materials using ultrasonic wave speeds

Manufacturing of metal components often results in significant texture, that is to say preferred orientations of their polycrystals. Since each crystal can be strongly anisotropic, this can give the component orientation-dependent material properties, affecting stiffness, thermal expansion, ultimate strength, and fatigue and creep resistance. So it is important to be able to measure texture, especially for high-value safety-critical components. Typically, the Orientation Distribution Function (ODF) of the crystals can be measured on exposed surfaces using EBSD, or in thin samples using neutron diffraction. But both are expensive, while there is currently no means to measure ODFs internally in real components. The authors have developed a method to determine internal texture from measurements of wave speeds at selected angles through the material. This is based on a convolution of wave speeds in a single crystal with the ODF, giving the resultant polycrystal wave speed angular function. Thus knowledge of the single crystal properties, together with wave speed measurements in the polycrystal, enables the ODF to be extracted. The method has been validated experimentally on flat samples of hexagonal and cubic materials, using ultrasound measurements in a water bath, and comparing the findings with neutron diffraction measurements, showing excellent agreement.

Rayleigh wave method of measuring the frequency-dependent shear modulus

The viscoelastic characterization of biomaterials is needed to develop compatible injectable implants for versatile medical applications. The present study is an investigation of injectable hydrogels for use in healing scarred soft tissues. A Rayleigh wave method was used to measure the frequency-dependent shear modulus of viscoelastic materials. A block of synthetic material was cast and excited by a shaker over a wide frequency range. The transverse velocity of the surface was recorded via an accelerometer and Laser Doppler Vibrometry (LDV). The linear phase delay validated the use of a transfer function method. The complex elastic modulus and the loss factor were obtained from the measured wave speed, and compared to data from a torsional rheometer. The benefits of the wave propagation approach compared to conventional parallel plate rheometry are that the material properties are acquired over a greater bandwidth. There is also a possibility of applying the same technique in vivo and in cell-seeded materials.