Estimation Of Shear Modulus Research Articles

Shear modulus of sand-rubber mixtures: element testing and constitutive modeling

In this study, a series of resonant column tests was conducted to measure the shear modulus of sand-rubber mixtures at small strain amplitudes (i.e. between 10−4% and 10−2%), considering different rubber percentages and confining stress levels. The results were then combined with data obtained by dynamic hollow cylinder tests to investigate shear modulus degradation of the mixtures over a wider shear strain range. Based on the test results, a new expression was proposed to improve the prediction of maximum shear modulus of sand-rubber mixtures using the modified equivalent void ratio concept. A new constitutive model was also developed for estimation of strain-dependent shear modulus of the mixtures based on the modified hyperbolic framework. The shear modulus of the mixtures was found to be a function of rubber percentage, confining stress, the modified equivalent void ratio and the relative shear stiffness of rubber and sand. The experimental data and the developed models showed that the shear modulus decreased with rubber percentage and increased with confining stress. Moreover, the reference shear strain of the modified hyperbolic model increased with both rubber percentage and confining stress while its curvature coefficient increased more considerably with rubber percentage compared to the confining stress.

Systematic quantification of differences in shear wave elastography estimates between linear-elastic and viscoelastic material assumptionsa).

Quantitative, accurate, and standardized metrics are important for reliable shear wave elastography (SWE)-based biomarkers. For over two decades, the linear-elastic material assumption has been employed in SWE modes. In recent years, viscoelasticity estimation methods have been adopted in a few clinical systems. The current study aims to systematically quantify differences in SWE estimates obtained using linear-elastic and viscoelastic material assumptions. An acousto-mechanical simulation framework of acoustic radiation force impulse-based SWE was created to elucidate the effect of material viscosity and shear modulus on SWE estimates. Shear modulus estimates exhibited errors up to 72% when a numerical viscoelastic phantom was assessed as linearly elastic. Shear modulus estimates of polyvinyl alcohol phantoms between rheometry and SWE following the Kelvin-Voigt viscoelastic model assumptions were not significantly different. However, the percentage difference in shear modulus estimates between rheometry and SWE using the linear-elastic assumption was 50.1%-62.1%. In ex vivo liver, the percentage difference in shear modulus estimates between linear-elastic and viscoelastic methods was 76.1%. These findings provide a direct and systematic quantification of the potential error introduced when viscoelastic tissues are imaged with SWE following the linear-elastic assumption. This work emphasizes the need to utilize viscoelasticity estimation methods for developing robust quantitative imaging biomarkers.

The relationship between estimates of puborectalis muscle shear modulus made with shear wave elastography and electromyography in healthy men

Aims:This study aimed to: (i) describe a method to estimate shear modulus of the male puborectalis muscle using shear wave elastography (SWE); (ii) investigate the relationship between changes in shear modulus and electromyography (EMG) of the left and right puborectalis muscle; (iii) investigate whether measures made at rest differ before and after a maximal voluntary contraction; and (iv) investigate whether rest measures are consistent over repeated submaximal contractions. Materials and Methods:Eleven males with no history of pelvic symptoms participated. Puborectalis muscle SWE was recorded using a transperineal ultrasound. Puborectalis EMG was recorded with a custom electrode stabilized to the anal mucosa with suction. Measures were made during rest and contractions at 10, 20, 30, 50 and 75% of maximal voluntary contraction (EMG). Correlation between normalized EMG and shear modulus data over contraction intensities was calculated (left; right). Amplitude of each measure at rest was compared before and after maximum voluntary contraction and before each submaximal contraction. Results:Group data showed strong linear correlations between shear modulus and EMG for the left r2=0.71 [SD 0.16; 95% CI 0.61−0.81], and right r2=0.56 [0.33; 0.35−0.76] puborectalis and there was no difference in the correlation between sides (p = 0.17), or between rest values of EMG or shear modulus before and after maximal and submaximal contractions (all p>0.31). Conclusions:This study confirms the viability of SWE for measurement of the puborectalis muscle in men and validity of changes in SWE as an estimate of shear modulus/stiffness of this muscle. Healthy men returned to rest values after contraction at different intensities.

Fast abdominal magnetic resonance elastography with simultaneous encoding of three-dimensional displacements

Three-dimensional (3D) magnetic resonance elastography (MRE) is more accurate than two-dimensional (2D) MRE; however, it requires long-term acquisition. This study aimed to reduce the acquisition time of abdominal 3D MRE using a new sample interval modulation (short-SLIM) approach that can acquire all three motions faster while reducing the prolongation of echo time and flow compensation.To this end, two types of phantom studies and an in vivo test of the liver in three healthy volunteers were performed to compare the performances of conventional spin-echo echo-planar (SE-EPI) MRE, conventional SLIM and short-SLIM. One phantom study measured the mean amplitude and shear modulus within the overall region of a homogeneous phantom by changing the mechanical vibration power to assess the robustness to the lowered phase-to-noise ratio in short-SLIM. The other measured the mean shear modulus in the stiff and background materials of a phantom with an embedded stiffer rod to assess the performance of short-SLIM for complex wave patterns with wave interference. The Spearman's rank correlation coefficient was used to assess similarity of elastograms in the rod-embedded phantom and liver between methods.The results of the phantom study changing the vibration power indicated that there was little difference between conventional MRE and short-SLIM. Moreover, the elastogram pattern and the mean shear modulus in the rod-embedded phantom in conventional SLIM and short-SLIM did not change for conventional MRE; the liver test also showed a small difference between the acquisition techniques.This study demonstrates that short-SLIM can provide MRE results comparable to those of conventional MRE. Short-SLIM can reduce the total acquisition time by a factor of 2.25 compared to conventional 3D MRE time, leading to an improvement in the accuracy of shear modulus estimation by suppressing the patient movements.

A new mathematical model for the estimation of shear modulus for unsaturated compacted soils

Small-strain shear modulus ( G) is an essential parameter for many geotechnical analyses. Most of shallow foundations are constructed in an unsaturated soil and the shear modulus of the unsaturated soil fluctuates because of the precipitation, evaporation, and rising of ground water table. In this paper, a new mathematical model is proposed for the estimation of the shear modulus function, Gunsat, which defines the relationship between small-strain modulus of unsaturated soil and matric suction. In the proposed model, the soil-water characteristic curve in the form of the degree of saturation is used as the input information. There are additional two parameters named n and C, which can be calibrated with the experimental data, are adopted in the proposed model. The estimated results show good agreement with the experimental data from literature. The proposed method can be used to track the tendency of Gunsat and minimize the data points from the laboratory tests.

Determination of Dynamic Properties of Fine-Grained Soils at High Cyclic Strains

Shear modulus (SM) and damping ratio (DR) are significant in seismic design and the performance of geotechnical systems. The evaluation of soil reactions to dynamic loads, such as earthquakes, blasts, train, and traffic vibrations, necessitates the estimation of dynamic SM and DR. The aim of this research is to determine the cyclic parameters of unsaturated soils in and around Peshawar, and how these properties depend upon the varied confining pressures and shear strains. Undisturbed samples were collected using Shelby tubes from five boreholes at different locations along Jamrud Road, Peshawar. The index properties (grain size distribution, plasticity index, and specific gravity) and dynamic properties of these samples were determined. Three samples of 100 mm in height and 50 mm in diameter were obtained from each Shelby tube. After preparing and mounting the sample in the triaxial cell, the sample is first saturated by increasing the cell and back pressures in increments of 50 kPa until the value of Skempton’s pore pressure parameter (B) reaches ≥ 0.96. Samples were consolidated at confining pressures of 150, 200, and 300 kPa, then subjected to cyclic shear strains of 0.2, 1, 2, 2.5, and 5%. Shear stress–strain hysteresis loops were plotted, and the values of SM and DR were calculated for each cycle. Generally, at shear strains of 0.2 and 1%, the slope of the loops is steep, and gradually becomes gentler at higher strains of 2, 2.5, and 5%. It is found that, with an increasing number of cycles, the SM and DR decrease. The SM decreases with increasing shear strain, whereas the DR increases at shear strains of 0.2–1%, then decreases for strains of 2, 2.5, and 5%. The confining pressure has more influence at a shear strain of 0.2–1%, while little effect has been observed at a shear strain of 2.2–5%. The values of SM are higher at higher confining pressures at a given shear strain. The results show higher stress values during the initial cycles because of the greater effective stress that developed in response to shear strain while, with an increase in the number of cycles, the pore water pressure gradually increases, thereby reducing the effective stress and weakening the bonds between soil particles. In dynamics, when the confining pressure increases, particles are closer to contact, so the travel paths of waves increase. The energy loss will increase, so DR will decrease.

Limitations of Curl and Directional Filters in Elastography

In the approaches to elastography, two mathematical operations have been frequently applied to improve the final estimate of shear wave speed and shear modulus of tissues. The vector curl operator can separate out the transverse component of a complicated displacement field, and directional filters can separate distinct orientations of wave propagation. However, there are practical limitations that can prevent the intended improvement in elastography estimates. Some simple configurations of wavefields relevant to elastography are examined against theoretical models within the semi-infinite elastic medium and guided waves in a bounded medium. The Miller–Pursey solutions in simplified form are examined for the semi-infinite medium and the Lamb wave symmetric form is considered for the guided wave structure. In both cases, we examine simple but practical wave combinations that can prevent the curl and directional filter operations from directly providing an improved measure of shear wave speed and shear modulus. Additional factors including signal-to-noise and the support of filters also restrict the applicability of these strategies for improving elastographic measures. Thus, some implementations of shear wave excitations applied to the body and to bounded structures within the body are shown to involve waves that are not easily resolved by the vector curl operator and directional filters. These limitations may be overcome by more advanced strategies or simple improvements in baseline parameters including the size of the region of interest and the number of shear waves propagated within.

Seismic imaging of reservoir heterogeneity using a network with high station density at The Geysers geothermal reservoir, CA, USA

We analyze results of high-resolution seismic imaging at The Geysers geothermal reservoir in northern California, USA, using a dense seismic network to image the spatial heterogeneity of the reservoir structure and flow paths. The project uses 92 seismic stations spaced at approximately 500 m over a 5 km × 5 km study area. Microseismic data for more than 17,000 earthquakes have been acquired over a period of 13 months and automatically processed for P- and S-wave phase arrival times. The data are subsequently inverted using a joint inversion approach to image the spatial heterogeneity of the reservoir including the 3D P- and S-wave velocity structure and [Formula: see text]/[Formula: see text] ratio, and to locate earthquake hypocenters. The resulting tomographic images are appraised by integration into The Geysers’ 3D reservoir model and by a spatial correlation to the injection and production wells. Spatial correlation of P-wave velocity images to water injection and steam production wells reveal higher velocities below injection wells, due to higher water saturation, and lower velocities in the vicinity of steam-producing wells, due to the presence of steam in the surrounding reservoir rocks. The spatial correlation of [Formula: see text]/[Formula: see text] to steam in the reservoir indicates decreased estimates in the vicinity of steam production wells. In contrast, the [Formula: see text]/[Formula: see text] ratio reveals high values in the reservoir for regions near water injection wells and along the potential flow path of water through the reservoir. The estimates of shear modulus indicate high values in a region of competent graywacke, which is known for a lack of fractures and steam production, and low values in a region that is dominated by water flow, suggesting that fractured rock created a pathway for the water through the reservoir. The heterogeneity observed in the S-wave velocities indicates a compartmentalized reservoir, which correlates spatially with fault projections in the 3D reservoir model.

Laboratory investigation on liquefaction of sands and cemented sand mixes

ABSTRACT Liquefaction is considered one of the most common phenomena resulting in serious damage during earthquakes. Appropriate estimation of liquefaction potential, damping characteristics and shear modulus of soil under dynamic loading is crucial for precise dynamic response analysis and soil modelling problems. The present paper emphasises the influence of relative density, confining pressure, and shear strain on the cyclic response of sand specimens. A parametric study comprising varying relative densities (35–65%), confining pressures (100–150 kPa), and shear strain (0.015–1.3%) under 1 Hz loading frequency was conducted in the laboratory. The sand samples were subjected to a series of consolidated undrained cyclic triaxial tests. It is observed that with an increase in confining pressure and relative density, the pore pressure ratio reduced; whereas an increase in pore pressure ratio was witnessed with an increase in shear strain. The influence of cement inclusion on the cyclic response of the specimens is evaluated for varying cement contents (1–4%). The addition of 4% cement considerably enhanced the strength of sand and arrested the liquefaction instigation.

Estimation of Shear Modulus and Hardness of High-Entropy Alloys Made from Early Transition Metals Based on Bonding Parameters

The relationship between the tendencies towards rigidity (measured by shear modulus, G) and hardness (measured by Vickers hardness, HV) of early transition metal (ETM)-based refractory high-entropy alloys (RHEA) and bond parameters (i.e., valence electron concentration (VEC), enthalpy of mixing (ΔHmix)) was investigated. These bond parameters, VEC and ΔHmix, are available from composition and tabulated data, respectively. Based on our own data (9 samples) and those available from the literatures (47 + 27 samples), it seems that for ETM-based RHEAs the G and HV characteristics have a close correlation with the bonding parameters. The room temperature value of G and HV increases with the VEC and with the negative value of ΔHmix. Corresponding equations were deduced for the first time through multiple linear regression analysis, in order to help design the mechanical properties of ETM refractory high-entropy alloys.

Nonlinear least-squares estimation of shear modulus and shear viscosity in viscoelastic media

Time-domain estimates of the shear wave speed are obtained by performing cross-correlations or by evaluating the time-to-peak for two laterally separated shear wave particle velocity waveforms, where the distance divided by the propagation time yields an approximate value for the shear wave speed. Challenges associated with these time-domain estimation approaches include increasing errors as the shear viscosity increases and the absence of an estimated value for the shear viscosity parameter which is responsible for the rapid attenuation of shear waves in soft tissue. To obtain a time-domain estimate of the shear viscosity that also provides an estimate for the shear wave speed, a nonlinear least squares estimation approach is applied to three-dimensional (3D) shear wave particle velocities computed for a shear elasticity of 1.5 kPa, shear viscosities of 1, 2, 3, and 4 Pa.s, and a realistic simulated 3D acoustic radiation force excitation. The results show cross-correlations tend to over-estimate the value of the shear wave speed, the nonlinear least squares approach tends to under-estimate the value of the shear wave speed, and the nonlinear least square approach produces more accurate estimates as the shear viscosity increases. Two-dimensional maps of each estimated parameter are also shown.

Reverberant magnetic resonance elastographic imaging using a single mechanical driver

Reverberant elastography provides fast and robust estimates of shear modulus; however, its reliance on multiple mechanical drivers hampers clinical utility. In this work, we hypothesize that for constrained organs such as the brain, reverberant elastography can produce accurate magnetic resonance elastograms with a single mechanical driver. To corroborate this hypothesis, we performed studies on healthy volunteers (n = 3); and a constrained calibrated brain phantom containing spherical inclusions with diameters ranging from 4–18 mm. In both studies (i.e. phantom and clinical), imaging was performed at frequencies of 50 and 70 Hz. We used the accuracy and contrast-to-noise ratio performance metrics to evaluate reverberant elastograms relative to those computed using the established subzone inversion method. Errors incurred in reverberant elastograms varied from 1.3% to 16.6% when imaging at 50 Hz and 3.1% and 16.8% when imaging at 70 Hz. In contrast, errors incurred in subzone elastograms ranged from 1.9% to 13% at 50 Hz and 3.6% to 14.9% at 70 Hz. The contrast-to-noise ratio of reverberant elastograms ranged from 63.1 to 73 dB compared to 65 to 66.2 dB for subzone elastograms. The average global brain shear modulus estimated from reverberant and subzone elastograms was 2.36 ± 0.07 kPa and 2.38 ± 0.11 kPa, respectively, when imaging at 50 Hz and 2.70 ± 0.20 kPa and 2.89 ± 0.60 kPa respectively, when imaging at 70 Hz. The results of this investigation demonstrate that reverberant elastography can produce accurate, high-quality elastograms of the brain with a single mechanical driver.

Resonant column and cyclic torsional shear tests on Sutlej river sand subjected to the seismicity of Himalayan and Shivalik hill ranges: A case study

The study of site-specific dynamic properties of soil holds vital importance in many geotechnical engineering problems for the region holding high active seismicity. The Sutlej River basin, a valley and high-risk seismic zone in the north-eastern part of the Punjab state, has been considered for the study. The site-specific shear modulus reduction curves and material damping ratio curves for a range of shear strain amplitudes have been developed under varying experimental conditions of confining pressure, relative density, and loading frequency using the resonant column (RC) tests and cyclic torsional shear (CTS) tests. The study addresses the usage of two testing approaches, i.e., resonant column test (RC) and cyclic torsional shear test (CTS), for the estimation of shear modulus and damping ratio values at varying shear strain amplitudes. The regression analysis has been performed for the two testing techniques viz. RC and CTS to study the sensitivity of shear modulus values and material damping ratio values towards varying experimental conditions. The shear modulus and damping ratio values determined from cyclic torsional shear tests were observed to have great dependency on the frequency of loading. The knowledge of site-specific dynamic properties will support practical interpretation for the geotechnical engineering problems in the region.

High-Frequency Ultrasound Elastography for Assessing Elastic Properties of Skin and Scars.

Scars are a type of fibrous tissue that typically forms during the wound healing process to replace damaged skin. Because studies have indicated a high correlation between scar stiffness and clinical symptoms, assessing the mechanical properties of scar is crucial for determining an appropriate treatment strategy and evaluating the treatment's efficacy. Shear wave elastography (SWE) is a common technique for measuring tissue elasticity. Because scars are typically a few millimeters thick, they are thin-layer tissues, and therefore, the dispersion effect must be considered to accurately estimate their elasticity. In this study, high-frequency ultrasound (HFUS) elastography was proposed for estimating the elastic properties of scars by using the Lamb wave model (LWM). An external vibrator was used to generate elastic waves in scar tissue and skin, and the propagation of the elastic waves was tracked through 40-MHz ultrafast ultrasound imaging. The elasticity was estimated through shear wave models (SWMs) and LWMs. The effectiveness of using HFUS elastography was verified through phantom and human studies. The phantom experiments involved bulk phantoms with gelatin concentrations of 7% and 15% and 2-4-mm-thick thin-layer 15% gelatin phantoms. The studies of three patients with eight cases of scarring were also conducted. The phantom experimental results demonstrated that the elasticity estimation biases for the thin-layer mediums were approximately -36% to -50% and 3% to -9% in the SWMs and LWMs, respectively, and the estimated shear moduli were 12.8 ± 5.4 kPa and 74.8 ± 26.8 kPa for healthy skin and scar tissue, respectively. All the results demonstrated that the proposed HFUS elastography has a great potential for improving the accuracy of elasticity estimations in clinical dermatological diagnoses.

Diastolic function: modeling left ventricular untwisting as a damped harmonic oscillator

Objective. We developed a method using cardiovascular magnetic resonance imaging to model the untwisting of the left ventricle (LV) as a damped torsional harmonic oscillator to estimate shear modulus (intrinsic myocardial stiffness) and frictional damping, then applied this method to evaluate the torsional stiffness of patients with resistant hypertension (RHTN) compared to a control group. Approach. The angular displacement of the LV during diastole was measured. Myocardial shear modulus and damping constant were determined by solving a system of equations modeling the diastolic untwisting as a damped, unforced harmonic oscillator, in 100 subjects with RHTN and 36 control subjects. Main Results. Though overall torsional stiffness was increased in RHTN (41.7 (27.1–60.7) versus 29.6 (17.3–35.7) kdyn*cm; p = 0.001), myocardial shear modulus was not different between RHTN and control subjects (0.34 (0.23–0.50) versus 0.33 (0.22–0.46) kPa; p = 0.758). RHTN demonstrated an increase in overall diastolic frictional damping (6.13 ± 3.77 versus 3.35 ± 1.70 kdyn*cm*s; p < 0.001), but no difference in damping when corrected for the overlap factor (74.3 ± 25.9 versus 68.0 ± 24.0 dyn*s/cm3; p = 0.201). There was an increase in the polar moment (geometric component of stiffness; 11.47 ± 6.95 versus 7.58 ± 3.28 cm4; p <0.001). Significance. We have developed a phenomenological method, estimating the intrinsic stiffness and relaxation properties of the LV based on restorative diastolic untwisting. This model finds increased overall stiffness in RHTN and points to hypertrophy, rather than tissue- level changes, as the major factor leading to increased stiffness.

Optical coherence elastography for assessing the influence of intraocular pressure on elastic wave dispersion in the cornea

The cornea is a highly specialized organ that relies on its mechanical stiffness to maintain its aspheric geometry and refractive power, and corneal diseases such as keratoconus have been linked to abnormal tissue stiffness and biomechanics. Dynamic optical coherence elastography (OCE) is a clinically promising non-contact and non-destructive imaging technique that can provide measurements of corneal tissue stiffness directly in vivo. The method relies on the concepts of elastography where shear waves are generated and imaged within a tissue to obtain mechanical properties such as tissue stiffness. The accuracy of OCE-based measurements is ultimately dependent on the mathematical theories used to model wave behavior in the tissue of interest. In the cornea, elastic waves propagate as guided wave modes which are highly dispersive and can be mathematically complex to model. While recent groups have developed detailed theories for estimating corneal tissue properties from guided wave behavior, the effects of intraocular pressure (IOP)-induced prestress have not yet been considered. It is known that prestress alone can strongly influence wave behavior, in addition to the associated non-linear changes in tissue properties. This present study shows that failure to account for the effects of prestress may result in overestimations of the corneal shear moduli, particularly at high IOPs. We first examined the potential effects of IOP and IOP-induced prestress using a combination of approximate mathematical theories describing wave behavior in thin plates with observations made from data published in the OCE literature. Through wave dispersion analysis, we deduce that IOP introduces a tensile hoop stress and may also influence an elastic foundational effect that were observable in the low-frequency components of the dispersion curves. These effects were incorporated into recently developed models of wave behavior in nearly incompressible, transversely isotropic (NITI) materials. Fitting of the modified NITI model with ex vivo porcine corneal data demonstrated that incorporation of the effects of IOP resulted in reduced estimates of corneal shear moduli. We believe this demonstrates that overestimation of corneal stiffness occurs if IOP is not taken into consideration. Our work may be helpful in separating inherent corneal stiffness properties that are independent of IOP; changes in these properties and in IOP are distinct, clinically relevant issues that affect the cornea health.

Fast magnetic resonance elastography with multiphase radial encoding and harmonic motion sparsity based reconstruction

Objective. To achieve fast magnetic resonance elastography (MRE) at a low frequency for better shear modulus estimation of the brain. Approach. We proposed a multiphase radial DENSE MRE (MRD-MRE) sequence and an improved GRASP algorithm utilizing the sparsity of the harmonic motion (SH-GRASP) for fast MRE at 20 Hz. For the MRD-MRE sequence, the initial position encoded by spatial modulation of magnetization (SPAMM) was decoded by an arbitrary number of readout blocks without increasing the number of phase offsets. Based on the harmonic motion, a modified total variation and temporal Fourier transform were introduced to utilize the sparsity in the temporal domain. Both phantom and brain experiments were carried out and compared with that from multiphase Cartesian DENSE-MRE (MCD-MRE), and conventional gradient echo sequence (GRE-MRE). Reconstruction performance was also compared with GRASP and compressed sensing. Main results. Results showed the scanning time of a fully sampled image with four phase offsets for MRD-MRE was only 1/5 of that from GRE-MRE. The wave patterns and estimated stiffness maps were similar to those from MCD-MRE and GRE-MRE. With SH-GRASP, the total scan time could be shortened by additional 4 folds, achieving a total acceleration factor of 20. Better metric values were also obtained using SH-GRASP for reconstruction compared with other algorithms. Significance. The MRD-MRE sequence and SH-GRASP algorithm can be used either in combination or independently to accelerate MRE, showing the potentials for imaging the brain as well as other organs.

Estimating maximum shear modulus (G0) using adaptive neuro-fuzzy inference system (ANFIS)

Realistic estimation of soil behavior is dependent on considering very small and small strain domains. Lengthy formulas proposed in the literature have limited predictive power for estimation of maximum shear modulus, G0. The aim of this study is to overcome this drawback. Theoretical aspects of fuzzy sets and adaptive neuro-fuzzy inference system (Anfis) are presented. Then, Anfis is implemented within a logical platform that adapts itself with available data to estimate and describe G0.

Development of Surface Level Seismic Hazard Maps Considering Local Soil Conditions for the State of Haryana, India

Abstract An extensive ground response analysis has been carried out in order to consider the effect of local soil conditions on surface level strong ground motions in the state of Haryana, India. Non-linear approach has been adopted to analyze 81 sites drilled up to refusal covering the entire state. It has been observed that 75 sites fall under site class D (medium dense soils), 4 sites under site class C (very dense soils), whereas only 2 sites fall under site class E (loose soils) as per the provisions of National Earthquake Hazard Reduction Program (NEHRP). For the estimation of low strain shear modulus (Gmax) using SPT N-value for different type of soils, various correlations have been used due to non-availability of in-situ measured values of shear wave velocity (Vs). The standard backbone curves for clays and sands have been used in the study in the absence of site-specific shear modulus degradation and damping ratio curves. The recorded acceleration time histories of the Ms 7.0 1991 Uttarkashi earthquake, having a focal depth of 10 km with PGA (g) ranging from 0.05g to 0.31g, have been used as input motion for the analysis. Amplification factors for peak ground acceleration (PGA) and spectral acceleration (Sa) for site class D have been calculated which are found to be comparable with those reported in NEHRP provisions. However, the site-specific hazard parameters determined for the tectonic setup of the seismic study region are quite different from that suggested by Indian standard code of practice.

Presurgical tear characteristics and estimated shear modulus as predictors of repair integrity and shoulder function one year after rotator cuff repair.

BackgroundRotator cuff repair provides pain relief for many patients; however, retears are relatively common and affect approximately 20%-70% of patients after repair. Although magnetic resonance imaging (MRI) offers the ability to assess tissue characteristics such as tear size, retraction, and fatty infiltration, it provides little insight into the quality of the musculotendinous tissues the surgeon will encounter during surgery. However, shear wave elastography (SWE) could provide an indirect assessment of quality (ie, stiffness) by measuring the speed of shear waves propagating through tissue. The objective of this study was to determine the extent to which estimated shear modulus predicts repair integrity and functional outcomes 1 year after rotator cuff repair.MethodsThirty-three individuals scheduled to undergo arthroscopic rotator cuff repair were enrolled in this study. Before surgery, shear modulus of the supraspinatus tendon and muscle was estimated using ultrasound SWE. MRIs were obtained before and 1 year after surgery to assess tear characteristics and repair integrity, respectively. Shoulder strength, range of motion, and patient-reported pain and function were assessed before and after surgery. Functional outcomes were compared between groups and across time using a two-factor mixed model analysis of variance. Stepwise regression with model comparison was used to investigate the extent to which MRI and shear modulus predicted repair integrity and function at 1 year after surgery.ResultsAt 1 year after surgery, 56.5% of patients had an intact repair. No significant differences were found in any demographic variable, presurgical tear characteristic, or shear modulus between patients with an intact repair and those with a recurrent tear. Compared with presurgical measures, patients in both groups demonstrated significant improvements at 1 year after surgery in pain (P < .01), self-reported function (P < .01), range of motion (P < .01), and shoulder strength (P < .01). In addition, neither presurgical MRI variables (P > .16) nor shear modulus (P > .52) was significantly different between groups at 1 year after surgery. Finally, presurgical shear modulus generally did not improve the prediction of functional outcomes above and beyond that provided by MRI variables alone (P > .22).ConclusionAlthough SWE remains a promising modality for many clinical applications, this study found that SWE-estimated shear modulus did not predict repair integrity or functional outcomes at 1 year after surgery, nor did it add to the prediction of outcomes above and beyond that provided by traditional presurgical MRI measures of tear characteristics. Therefore, it appears that further research is needed to fully understand the clinical utility of SWE for musculoskeletal tissue and its potential use for predicting outcomes after surgical rotator cuff repair.