Increasing Shear Wave Velocity Research Articles

Detection of natural pulse waves (PWs) in 3D using high frame rate imaging for anisotropy characterization

IntroductionNumerous studies have shown that natural mechanical waves have the potential to assess the elastic properties of the myocardium. When the Aortic and Mitral valves close, a shear wave is produced, which provides insights into tissue stiffness. In addition, the Atrial Kick (AK) generates a wave similar to Pulse Waves (PWs) in arteries, providing another way to assess tissue stiffness. However, tissue anisotropy can also impact PW propagation, which is currently underexplored. This study aims to address this gap by investigating the impact of anisotropy on PW propagation in a phantom.MethodsTube phantoms were created using Polyvinyl Alcohol (PVA). Anisotropy was induced between two sets of two freeze-thaw cycles by stretching and twisting the material. The study first tests and validates the procedure of making helical anisotropic vessel phantoms using the shear wave imaging technique (by estimating the shear wave speed at different probe angles). Using plane wave ultrasound tomography synchronized with a peristaltic pump, 3D high frame rate imaging is performed and used to detect the 3D propagation pattern of PW for each manufactured vessel phantom. Finally, the study attempts to extract the anisotropic coefficient of the vessel using pulse wave propagation angle.ResultsThe Shear wave imaging results obtained for the isotropic vessel show very similar values for each probe angle. On the contrary, the results obtained for the axial anisotropy vessel show a region with a higher shear wave speed at about 0°, corresponding to the long axis of the vessel. Finally, the results obtained for the helical anisotropy depicted increasing shear wave velocity value from −20° to 20°. For the axial phantom, the wavefront of the pulse wave is perpendicular to the long axis of the vessel, while oriented for the helical anisotropic vessels phantom. The pulse wave propagation angle increased with the number of twists made during the vessel manufacturing.DiscussionThe results show that anisotropy can be induced in PVA vessel phantoms by stretching and twisting the material in freeze-thaw cycles. The findings also suggest that vessel anisotropy affects pulse wave propagation angles. Estimating the pulse wave propagation angle may be interesting in characterizing tissue anisotropy in organs where such waves are naturally present.

Periodic foundation piles for the seismic protection of structures

This study introduces a novel solution for seismic protection of structures based on resonant metamaterials, named Periodic Foundation Piles, which can be integrated with deformable soil deposits in order to filter shear waves in a specific frequency range. A Periodic Foundation Pile consists of an array of vertical periodic structural elements containing internal resonators suitably tuned to one or more natural frequencies of the soil deposit. The proposed system is equivalent to a discontinuous foundation pile and can be installed in the ground with approximately the same procedure for piles, thus making it suitable also for applications in existing structures. The performance of the Periodic Foundation Piles in reducing the amplitude of a seismic motion has been shown through non-linear site response analyses carried out using real acceleration records as input motion. A soil deposit with an increasing shear wave velocity profile has been considered; the nonlinear behaviour of the soil has been modelled through the Iwan model, calibrated using a normalized secant shear modulus curve accounting for the influence of the confining pressure on the stress-strain relationship. Numerical results, presented in terms of peak acceleration, horizontal displacement and shear deformation profiles, as well as in terms of Fourier amplitude and response spectra, indicate that Periodic Foundation Piles may noticeably reduce the amplitudes of seismic motion in a suitable frequency range, hence potentially representing an innovative strategy to mitigate the effects of earthquakes on structures.

Simultaneous proton resonance frequency T1 - MR shear wave elastography for MR-guided focused ultrasound multiparametric treatment monitoring.

To develop an efficient MRI pulse sequence to simultaneously measure multiple parameters that have been shown to correlate with tissue nonviability following thermal therapies. A 3D segmented EPI pulse sequence was used to simultaneously measure proton resonance frequency shift (PRFS) MR thermometry (MRT), T1 relaxation time, and shear wave velocity induced by focused ultrasound (FUS) push pulses. Experiments were performed in tissue mimicking gelatin phantoms and ex vivo bovine liver. Using a carefully designed FUS triggering scheme, a heating duty cycle of approximately 65% was achieved by interleaving FUS ablation pulses with FUS push pulses to induce shear waves in the tissue. In phantom studies, temperature increases measured with PRFS MRT and increases in T1 correlated with decreased shear wave velocity, consistent with material softening with increasing temperature. During ablation in ex vivo liver, temperature increase measured with PRFS MRT initially correlated with increasing T1 and decreasing shear wave velocity, and after tissue coagulation with decreasing T1 and increasing shear wave velocity. This is consistent with a previously described hysteresis in T1 versus PRFS curves and increased tissue stiffness with tissue coagulation. An efficient approach for simultaneous and dynamic measurements of PRSF, T1 , and shear wave velocity during treatment is presented. This approach holds promise for providing co-registered dynamic measures of multiple parameters, which correlates to tissue nonviability during and following thermal therapies, such as FUS.

DIAGNOSTIC VALUE OF MULTIPARAMETRIC ULTRASOUND EXAMINATION IN PATIENTS WITH RECURRENT TONSILITIS

The problem of recurrent tonsillitis in the world is still highly relevant. A clear algorithm for the diagnosis and treatment of patients with this pathology is still being developed and improved. Thanks to the latest technologies, modernization of equipment and improvement of knowledge of medical workers, it is possible to diagnose this disease better and, consequently, to decide on further treatment.
 Aim. Determine the informative value of shear wave elastography as an additional objective method for the diagnostics of recurrent tonsillitis.
 Materials and methods. 24 participants were enrolled in the research. Age structure: children of primary school age (6-10 years) - 14 people, teenagers (10-15 years) - 6 people, high school age (15-17 years) - 2 people, adults (22-35 years) - 2 people. Criteria for inclusion in the research - from 4 to 6 episodes of tonsillitis per year for the last 2 years. The patients' anamnesis was carefully collected, and ENT examination, paying special attention to the presence of symptoms of "underactivity" of the tonsils, shear wave elastometry and elastography of the palatine and peritoneal tonsils were performed as one of the newest methods of ultrasound examination. Longitudinal and transverse scans of the palatine tonsils and surrounding structures were performed. The obtained data were recorded in the patient's examination card for further analysis.
 In general, the main indicators were identified, which were further analyzed - the size of the tonsils, transverse size and stiffness of the paratonsillar space, colors, which mapped the examined structures, the size of regional maxillary lymph nodes.
 Results. After collecting the participants’ anamnesis, the main common feature was identified - experiencing 4 to 6 episodes of tonsillitis per year for the past 2 years, and on ENT examination – fixation of the tonsils, which indicated fibrotic changes in the paratonsillar space, which became one of the main criteria for inclusion of patients in this research. It is an objective criterion for recurrent tonsillitis. Elastometry and elastography of peritonsillar structures revealed other important objective features of recurrent tonsillitis - the shear waves velocity (stiffness of the peritonsillar space) higher than 2.0 m/sec which is mapped in red and burgundy color. Mapping of the tonsils themselves was less informative due to insignificant clinical significance. More important was the mapping of paratonsillar spaces. An additional objective criterion was the size of the maxillary lymph nodes as regional lymph nodes for the palatine tonsils. They ranged from 10.5 mm to 20.5 mm, which is larger than normal values.
 Conclusions. According to the result of the research, the following signs of recurrent tonsillitis were identified: fixation of the palatine tonsils, increased shear wave velocity (stiffness index) in the peritonsillar space on elastometry (higher than 2 m/sec), that hypothetically, can be considered as indicating fibrosis of the peritonsillar space, mapping of peritonsillar space structures with colors from green and blue to red with areas of burgundy (in normal tissues green, blue, sometimes yellow colors are seen), enlarged maxillary lymph nodes, as regional for the palatine tonsils.
 Thus, we can confirm the high informative value of shear wave elastometry and elastography as an additional objective method of visualization in patients with recurrent tonsillitis.

Experimental study and numerical simulation on dynamic soil‐structure interaction under earthquake excitations

Soil-structure interaction (SSI) phenomena subjected to seismic loadings are investigated in this study. Firstly, shaking table tests on dynamic soil‐structure interaction subjected to seismic loadings are carried out, and SSI effects are analyzed through a comparative study between the soil-structure system and the rigid foundation condition. Then, a corresponding numerical model on the SSI tests is presented. In the finite element model, a bounding surface plasticity model and an equivalent linear method are separately used for simulating the nonlinear behavior of soil. It turns out that the calculated results by the bounding surface plasticity model agree much better with the experimental results. Finally, the effects of different soil types and structural properties on soil-structure interaction are discussed by numerical parametric study. The results show that SSI effects noticeably mitigate the dynamic response of structure, and the closer the frequency of superstructure to the soil frequency, the more obvious the effect of soil-structure interaction. With increased shear wave velocity of soil, the impact of soil-structure interaction weakens. It is important for studying the impact of SSI on structural responses and practical engineering design purposes.

The river harbour of Ostia Antica - stratigraphy, extent and harbour infrastructure from combined geophysical measurements and drillings

We performed a combined geophysical and geoarchaeological survey of the harbour of ancient Ostia, Italy, to investigate the extent of the former harbour basin, the sedimentary infill and possible building remains around the harbour. Besides geoarchaeological results the paper highlights the advantage of combining vibracore drilling with different geophysical prospection methods, which are sensitive to different physical soil parameters. Geophysical methods applied were electrical resistivity tomography (ERT), ground penetrating radar (GPR) and seismics with shear and compressional waves. The extent and shape of the harbour basin were determined by ERT profiling. The ERT profiles were compiled into a 3D-model showing that the early lagoonal harbour basin was at least 100 m × 50 m wide. Its southern border was confirmed by GPR measurements clearly imaging the former land-water transition and the onset of ancient onshore building construction. At its eastern border a consolidated horizon could be mapped in 2–3 m depth by compressional wave tomography. This horizon most likely represents a cemented ramp, a small part of which had been excavated in a previous study. The sedimentary fill of the former harbour basin was investigated by a combination of vibracoring, ERT and seismics. The ERT profiles serve for inter- and extrapolating the vibracore stratigraphy from the coring locations over the whole harbour area. It turned out that one sedimentary unit, which is important for the harbour development, could not be resolved by ERT but clearly shows up in seismic velocity-depth profiles instead. It is a thin coarse-grained high-energy layer in 1–2 m depth, which was caused by a tsunami according to a previous study. This layer separates two harbour phases: an older lagoonal harbour phase underneath and a younger fluvial harbour phase above it. The high-energy layer represents a thin band of 100% increased shear wave velocity compared to the more fine-grained layers, in which it is embedded. This study is the first to show that tsunami-type sedimentary layers may be mapped by shear wave profiling.

Estimating ground motion incoherence through finite source simulation: a case study of the 1980 El-Asnam Earthquake

Spatial variability of ground motions has significant influence on dynamic response of extended structures such as bridges and tunnels. In this study, the widely used finite-source ground motion simulation approach, the so-called Empirical Green’s Function (EGF) method, is extended to synthesize seismic motions across an array of stations located at bedrock in the epicentral region of the 1980 El-Asnam region (North-West Algeria). The target event being simulated is the October 10 1980 \( M_{s} = 7.2 \) Earthquake, and the EGF is obtained from the ground motion recorded at Sogedia Factory station during the 8 November 1980 \( M_{L} = 5.6 \) aftershock. Coherency functions are then estimated from the simulated ground accelerations. A parametric study investigating the influence of shear wave velocity, earthquake magnitude, and epicentral distance is conducted by simulating ground acceleration for different scenarios using the Hybrid Green’s Function method. The main finding of the study is that finite source effects can cause significant loss in coherency at bedrock in the near-field. In the far-field, the source effect alone does not seem to produce incoherent motion, which implies that scattering and local site effects could be dominating there. Furthermore, coherency functions are found to be more sensitive to inter-station separation in the near-field than in the far-field. Increasing shear wave velocity seems to increase coherency functions, and larger earthquakes seem to produce more incoherent motion than smaller ones. The simulation method presented here produces incoherent motion mainly due to the finite source effect, while path effects are partially accounted for through the EGF, and local site effects are not considered. In this sense, the estimated coherency functions represent that of plane waves. A parametric model of plane wave coherency is calibrated and presented based on the simulation results. The results indicate that the parametric model can be used as a first approximation, and at least an upper bound of lagged coherency in the near-field region of the El-Asnam Earthquake scenario. This model could be useful in random vibration analysis or generation of spatially variable ground motion for time history analysis of lifeline structures in the study area.

Prediction equations for generalized interstory drift spectrum considering near-fault ground motions

This paper presents a new ground motion prediction equation for the estimation of generalized interstory drift spectrum (GIDS). This parameter estimates, through an approximate method, the maximum interstory drift ratio in multistory buildings responding elastically to a given ground motion record. The models presented by this study is developed empirically by regression of the database that was selected from the NGA-West 1 for fault rupture distances of <60 km. The dataset comprised 851 corrected and processed strong-motion records of earthquakes between M w 5.2 and 7.9. The model is bass on a function of earthquake magnitude, distance from source to site, local average shear wave velocity, nonlinear soil response, sediment depth, rupture dip, faulting mechanism, and hanging-wall effect. This equation was derived from a stable algorithm for regression analysis called mixed-effects model. The algorithm was used to develop ground motion prediction equation for the estimation of GIDS in three different lateral resisting systems with oscillator periods ranging from 0.05 to 5.0 s. These structural systems with bending lateral deformation (shear walls), shear lateral deformation (moment-resisting frames), and hybrid lateral deformation (combination of moment-resisting frames and shear walls) are selected to maintain a general prospect with respect to the effect of the seismic source and site parameters on GIDS. The results showed that increasing shear wave velocity causes a decrease in the influence of the type of lateral resisting system on the maximum interstory drift ratio. Moreover, a comparison of different systems indicates that maximum interstory drift ratio of moment-resisting frames is less dependent on the distance from causative fault than shear wall structure.

Liquefaction potential of soils around circular double tunnels

The aim of this paper is to investigate the effect of underground circular tunnels on cyclic behavior and liquefaction potential of soils surrounding them. For this purpose, an intensive numerical analyses scheme which includes three-dimensional, finite difference based total stress analyses on generic soil, tunnel and earthquake combinations has been performed. The effect of tunnel diameters, depth of tunnel center and the strength of soils on the maximum ground accelerations and liquefaction potential have been discussed in detail. The liquefaction potential is discussed in terms of both the factor of safety (FSliq) and liquefaction potential index. It is concluded that changing the diameter and support thickness of the tunnels does not make a remarkable change on peak ground accelerations. Similarly, the liquefaction potential of the soils considered does not depend on the diameter of the tunnel. However, it was shown that the most important parameters which are effective in peak ground acceleration and liquefaction potential are the depth of the tunnel and the rigidity of the soil in which the tunnel is constructed. The analyses showed that, the maximum ground acceleration values are observed in the middle of the two tunnels. Moreover, the peak ground acceleration value increases with increasing shear wave velocity and accordingly increases the resistance to liquefaction potential as expected. This study showed that, if a tunnel is to be built in a liquefaction prone zone, it should be constructed as deep as possible to reduce the probable risk of liquefaction.

A study on low strain integrity testing of platform-pile system using staggered grid finite difference method

To study the three-dimensional characteristics of wave propagation in platform-pile system, a three-dimensional computation model for transient vibration of platform-pile-soil system is established. Based on initial and boundary conditions, the numerical solution of this model is obtained. A MATLAB program is compiled through using staggered grid finite difference method. The dynamic response of the integrate pile in platform-pile-soil system is got under vertical impact force, and the reliability and feasibility of the numerical simulation are corroborated by comparing calculation result with measured data of low strain integrity testing of platform-pile system. The optimal sensor location at platform top is studied. The results show the position distancing the pile center 0.5R~0.6R (R is pile radius) is the optimal sensor location, which the line between sensor location and pile center parallels the short side. It plays a certain role in reducing three-dimensional interference through increasing shear wave velocity of surrounding soil and appropriately increasing the ratio of characteristic wavelength to pile radius. In addition, contact area has less influence on low strain integrity testing of platform-pile system.

A New Insight into Probabilistic Seismic Hazard Analysis for Central India

The Son-Narmada-Tapti lineament and its surroundings of Central India (CI) is the second most important tectonic regime following the converging margin along Himalayas-Myanmar-Andaman of the Indian sub-continent, which attracted several geoscientists to assess its seismic hazard potential. Our study area, a part of CI, is bounded between latitudes 18°–26°N and longitudes 73°–83°E, representing a stable part of Peninsular India. Past damaging moderate magnitude earthquakes as well as continuing microseismicity in the area provided enough data for seismological study. Our estimates based on regional Gutenberg–Richter relationship showed lower b values (i.e., between 0.68 and 0.76) from the average for the study area. The Probabilistic Seismic Hazard Analysis carried out over the area with a radius of ~300 km encircling Bhopal yielded a conspicuous relationship between earthquake return period (T) and peak ground acceleration (PGA). Analyses of T and PGA shows that PGA value at bedrock varies from 0.08 to 0.15 g for 10 % (T = 475 years) and 2 % (T = 2,475 years) probabilities exceeding 50 years, respectively. We establish the empirical relationships $$ {\text{ZPA}}_{(T = 475)} = 0.1146\;[V_{\text{s}} (30)]^{ - 0.2924}, $$ and $$ {\text{ZPA}}_{(T = 2475)} = 0.2053\;[V_{\text{s}} (30)]^{ - 0.2426} $$ between zero period acceleration (ZPA) and shear wave velocity up to a depth of 30 m [V s (30)] for the two different return periods. These demonstrate that the ZPA values decrease with increasing shear wave velocity, suggesting a diagnostic indicator for designing the structures at a specific site of interest. The predictive designed response spectra generated at a site for periods up to 4.0 s at 10 and 2 % probability of exceedance of ground motion for 50 years can be used for designing duration dependent structures of variable vertical dimension. We infer that this concept of assimilating uniform hazard response spectra and predictive design at 10 and 2 % probability of exceedance in 50 years at 5 % damping at bedrocks of different categories may offer potential inputs for designing earthquake resistant structures of variable dimensions for the CI region under the National Earthquake Hazard Reduction Program for India.

Differentiating Malignant From Benign Thickening of the Gallbladder Wall by the Use of Acoustic Radiation Force Impulse Elastography

The purpose of this study was to determine whether real-time elastography can differentiate gallbladder carcinoma from benign gallbladder wall thickening. Sonographic and real-time elastographic examinations were done in 125 of 2000 consecutive patients who had an increased gallbladder wall thickness of more than 3 mm. Shear wave velocities were determined for a normal gallbladder wall, a benign thickened gallbladder wall, and gallbladder carcinoma, and a value of 2.7 m/s was set as the cutoff to differentiate between benign and malignant wall thickening. Virtual touch and color maps of the gallbladder wall were also obtained. The final diagnosis was confirmed by histopathologic examination of the resected gallbladder or by guided fine-needle aspiration cytologic examination. Statistical analysis was done to determine the sensitivity and specificity of elastography for gallbladder carcinoma and benign wall thickening. Student t test and area under the receiver operating characteristic curve analyses were done to determine the statistical significance of the results. Elastography had sensitivity and specificity of 100% and 91.3%, respectively, for diagnosing gallbladder carcinoma with a mean shear wave velocity of 3.41 m/s (P < .0001) and an area under the curve of 0.92. False-positive findings of acute cholecystitis occurred in 8.5% of cases, which also had an increased shear wave velocity of greater than 2.7 m/s. The overall accuracy of elastography for differentiating gallbladder carcinoma from benign wall thickening was 92.8%. Elastography is an accurate technique for differentiating between benign and malignant gallbladder wall thickening and can be combined with sonography as the prime imaging tool for diagnosing gallbladder carcinoma at an early stage.

The use of fly ash to alter the engineering properties of artificial “model” clay

This article describes a procedure using fly ash to alter, for similitude purposes, the geotechnical engineering properties of artificial clay used in shaking table physical model studies. The fly ash used in this study acted as a chemically reactive material when mixed with an artificial kaolinite-bentonite model clay. When added to the model clay, the fly ash stiffened the soil (increased shear wave velocity) while lowering the soil’s undrained shear strength. To avoid increasing the strength of the model soil, the fly ash-clay mixture had to be thoroughly remolded at least several days after initial mixing. The article discusses an application of this model soil preparation procedure for a 1-g shaking table study of seismic soil-pile-superstructure interaction in a soft marine clay.