Stiffness Contrast Research Articles

In Vivo Imaging of Implanted Hyaluronic Acid Hydrogel Biodegradation.

Although the use of stem cell therapy for central nervous system (CNS) repair has shown considerable promise, it is still limited by the immediate death of a large fraction of transplanted cells owing to cell handling procedures, injection stress and host immune attack leading to poor therapeutic outcomes. Scaffolding cells in hydrogels is known to protect cells from such immediate death by shielding them from mechanical damage and by averting an immune attack after transplantation. Implanted hydrogels must eventually degrade and facilitate a safe integration of the graft with the surrounding host tissue. Hence, serial monitoring of hydrogel degradation in vivo is pivotal to optimize hydrogel compositions and overall therapeutic efficacy of the graft. We present here methods and protocols to use chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) as a non-invasive, label-free imaging paradigm to monitor the degradation of composite hydrogels made up of thiolated gelatin (Gel-SH), thiolated hyaluronic acid (HA-SH), and poly (ethylene glycol) diacrylate (PEGDA), of which the stiffness and CEST contrast can be fine-tuned by simply varying the composite concentrations and mixing ratios. By individually labeling Gel-S and HA-S with two distinct near-infrared (NIR) dyes, multispectral monitoring of the relative degradation of the components can be used for long-term validation of the CEST MRI findings.

Impact of fatigue loading on the surface of polyurethane treated in argon and acetylene plasma

Soft plasma-treated polymers have good prospects in the creation of biomedical products. Their application is associated with cyclic mechanical loads. The practical applicability of such coatings is unclear without investigating the effect of deformation on the structure of modified surfaces. Elastic polyurethane (synthetic two-phase polymer) was used in this work. Its surface was preliminarily cleaned from low-molecular fractions by argon plasma and then treated by plasma chemical decomposition of acetylene in argon plasma for 30...120 s. The structural and mechanical inhomogeneities of the obtained carbon-containing nanocoatings depend on the treatment time and were caused by the composition of the initial substrate. Uniaxial fatigue loading leads to the formation of transverse folds on the coatings in the unloaded state (a result of elastic-plastic deformation of the coating); under tension these folds are open and form local nanocracks. One of the variants of plasma modification did not give the formation of cracks; it is associated with the areas with a pronounced stiffness contrast of this coating.

Reconstructing the shear modulus contrast of linear elastic and isotropic media in quasi-static ultrasound elastography.

This study focuses on the reconstruction of the shear modulus contrast in linear elastic and isotropic media, in quasi-static ultrasound elastography. The method proposed is based on the variational formulation of the equilibrium equations and on the choice of adapted discretization spaces to estimate the parameters of interest. Experimental results obtained with CIRS phantoms are presented, for which regions with different mechanical properties can be clearly identified in the stiffness contrast maps. Elastic modulus images collected with a shear-wave elastography technique from a clinical ultrasound scanner (Aixplorer) are also provided for comparison. Results show very similar values for the modulus ratios determined by the two elastography approaches.

Phase field feature of inclined hydraulic fracture propagation in naturally-layered rocks under stress boundaries

The phase field feature of inclined hydraulic fracture propagation in naturally-layered rocks under stress boundaries is investigated by using a numerical method. Based on a phase field fracture model, the coupled governing equations of displacement field, phase field, and flow field concerning hydraulic fracturing in naturally-layered rocks were established. The equations were solved using the finite element method and the influences of initial stress field and stiffness contrast on the fracture patterns were deeply studied. The numerical simulations indicate that: 1) The ratio of vertical in-situ stress to horizontal in-situ stress (S v/S h) has a significant effect on propagation of the hydraulic fracture. With the increase in S v/S h, the hydraulic fracture deflects and propagates along the direction of S v, which is also the maximum in-situ stress; 2) The stiffness contrast of the two layers (E 1/E 2) has great influence on fracture penetration into the adjacent layer. For a low E 1/E 2, a singly-deflected scenario is observed because the fracture propagation is depressed by the stiff rock. With the increase in E 1/E 2, the hydraulic fracture more tends to penetrate into the adjacent layer.

On the fracture mechanism of rock-like materials with interbedded hard-soft layers under Brazilian tests

The fracture of layered rocks subjected to tensile stress is involved in various subsurface energy-related activities. Many studies have numerically investigated the fracture evolution behaviour and Brazilian tensile strength (BTS) of layered rock in Brazilian tests. However, the fracture mechanism of layered rocks, especially those with interbedded hard-soft layers, is still not well understood. This is mainly due to the fact that the layered rocks were often modelled as two-phase materials only consisting of either rock matrix with layer interfaces or hard and soft layers without explicitly considering layer interfaces. In this study, rock-like discs interbedded with hard and soft layers are prepared with a dimension of 40 mm in diameter and 15 mm in thickness. The uniaxial compressive strength (UCS), BTS, and Young’s modulus of hard layers are 49 MPa, 6.7 MPa, and 10 GPa, respectively, while those of soft layers are 17 MPa, 3.2 MPa, and 8.0 GPa, respectively. The layered discs are tested with inclination angles between 0° and 90° at 15° interval under Brazilian tests with a loading rate of 0.24 mm/min. Then, three-dimensional layered models comprised of soft layers, hard layers, and layer interfaces are numerically established. Their mechanical behaviours are described by a newly developed constitutive model that can capture the tensile and compressive damage of rock-like materials under various loading scenarios. After validating against experimental results, the effects of Young’s modulus of layer interface and mechanical contrast of hard-to-soft layers on the stress distribution, crack initiation and propagation mechanisms, and peak load of layered discs with various inclination angles are numerically explored. It is observed that the effects of interface stiffness and mechanical contrast ratio on the peak load and fracture mechanism are layer orientation dependent.

Effect of stiffness contrast on the dislocation equilibrium positions in a multi-layered structure

The equilibrium positions of two edge dislocations lying in the same gliding plane have been theoretically determined in a structure composed of a thin layer embedded in an infinite-size matrix of different elastic constants, when the two dislocations are symmetrically distributed with respect to the axis of symmetry of the problem parallel to the interfaces. When the Burgers vectors of the two dislocations are equal and the matrix is stiffer than the layer, the equilibrium positions have been found to be unstable in the central layer and stable in the matrix. No equilibrium position is found when the matrix is softer than the layer. When the Burgers vectors are of opposite sign (same norm and direction) and the layer is stiffer than the matrix, the equilibrium positions are stable in the central layer and unstable in the matrix, no equilibrium position being found when the layer is softer than the matrix.

Morphogenesis and cell ordering in confined bacterial biofilms

Biofilms are aggregates of bacterial cells surrounded by an extracellular matrix. Much progress has been made in studying biofilm growth on solid substrates; however, little is known about the biophysical mechanisms underlying biofilm development in three-dimensional confined environments in which the biofilm-dwelling cells must push against and even damage the surrounding environment to proliferate. Here, combining single-cell imaging, mutagenesis, and rheological measurement, we reveal the key morphogenesis steps of Vibrio cholerae biofilms embedded in hydrogels as they grow by four orders of magnitude from their initial size. We show that the morphodynamics and cell ordering in embedded biofilms are fundamentally different from those of biofilms on flat surfaces. Treating embedded biofilms as inclusions growing in an elastic medium, we quantitatively show that the stiffness contrast between the biofilm and its environment determines biofilm morphology and internal architecture, selecting between spherical biofilms with no cell ordering and oblate ellipsoidal biofilms with high cell ordering. When embedded in stiff gels, cells self-organize into a bipolar structure that resembles the molecular ordering in nematic liquid crystal droplets. In vitro biomechanical analysis shows that cell ordering arises from stress transmission across the biofilm-environment interface, mediated by specific matrix components. Our imaging technique and theoretical approach are generalizable to other biofilm-forming species and potentially to biofilms embedded in mucus or host tissues as during infection. Our results open an avenue to understand how confined cell communities grow by means of a compromise between their inherent developmental program and the mechanical constraints imposed by the environment.

Stress rotation – impact and interaction of rock stiffness and faults

Abstract. It has been assumed that the orientation of the maximum horizontal compressive stress (SHmax) in the upper crust is governed on a regional scale by the same forces that drive plate motion. However, several regions are identified where stress orientation deviates from the expected orientation due to plate boundary forces (first-order stress sources), or the plate wide pattern. In some of these regions, a gradual rotation of the SHmax orientation has been observed. Several second- and third-order stress sources have been identified in the past, which may explain stress rotation in the upper crust. For example, lateral heterogeneities in the crust, such as density and petrophysical properties, and discontinuities, such as faults, are identified as potential candidates to cause lateral stress rotations. To investigate several of these candidates, generic geomechanical numerical models are set up with up to five different units, oriented by an angle of 60∘ to the direction of shortening. These units have variable (elastic) material properties, such as Young's modulus, Poisson's ratio and density. In addition, the units can be separated by contact surfaces that allow them to slide along these vertical faults, depending on a chosen coefficient of friction. The model results indicate that a density contrast or the variation of Poisson's ratio alone hardly rotates the horizontal stress (≦17∘). Conversely, a contrast of Young's modulus allows significant stress rotations of up to 78∘, even beyond the vicinity of the material transition (>10 km). Stress rotation clearly decreases for the same stiffness contrast, when the units are separated by low-friction discontinuities (only 19∘ in contrast to 78∘). Low-friction discontinuities in homogeneous models do not change the stress pattern at all away from the fault (>10 km); the stress pattern is nearly identical to a model without any active faults. This indicates that material contrasts are capable of producing significant stress rotation for larger areas in the crust. Active faults that separate such material contrasts have the opposite effect – they tend to compensate for stress rotations.

Stress rotation – impact and interaction of rock stiffness and faults

Abstract. It has been assumed that the orientation of the maximum horizontal compressive stress ( SHmax ) in the upper crust is governed on a regional scale by the same forces that drive plate motion. However, several regions are identified where stress orientation deviates from the expected orientation due to plate boundary forces (first-order stress sources), or the plate wide pattern. In some of these regions, a gradual rotation of the SHmax orientation has been observed. Several second- and third-order stress sources have been identified in the past, which may explain stress rotation in the upper crust. For example, lateral heterogeneities in the crust, such as density and petrophysical properties, and discontinuities, such as faults, are identified as potential candidates to cause lateral stress rotations. To investigate several of these candidates, generic geomechanical numerical models are set up with up to five different units, oriented by an angle of 60 ∘ to the direction of shortening. These units have variable (elastic) material properties, such as Young's modulus, Poisson's ratio and density. In addition, the units can be separated by contact surfaces that allow them to slide along these vertical faults, depending on a chosen coefficient of friction. The model results indicate that a density contrast or the variation of Poisson's ratio alone hardly rotates the horizontal stress ( ≦17 ∘ ). Conversely, a contrast of Young's modulus allows significant stress rotations of up to 78 ∘ , even beyond the vicinity of the material transition ( >10 km ). Stress rotation clearly decreases for the same stiffness contrast, when the units are separated by low-friction discontinuities (only 19 ∘ in contrast to 78 ∘ ). Low-friction discontinuities in homogeneous models do not change the stress pattern at all away from the fault ( >10 km ); the stress pattern is nearly identical to a model without any active faults. This indicates that material contrasts are capable of producing significant stress rotation for larger areas in the crust. Active faults that separate such material contrasts have the opposite effect – they tend to compensate for stress rotations.

Design ductile and work-hardenable composites with all brittle constituents

Metallic glasses, like many other glasses and ceramics, generally have zero tensile ductility. Distinct from common wisdom which seeks to toughen brittle glasses with ductile phases, we show that composites made from two brittle glasses can be ductile, strong and even harden under tension as a result of microstructure and stiffness contrast. Using molecular dynamics simulations, we designed and tested composites consisting of alternating wavy nanofilaments of two brittle glasses with different stiffness. The composites exhibit failure strain over 40% and strain hardening modulus over 2 GPa. The tensile ductility is determined by both the flexibility of nanofilaments and the propensity of crack deflection, with which a ductile composite design map can be constructed. The strain hardening is due to filament alignment analogous to linear polymer. The brittle-brittle composite design strategy proposed here is not material-specific and should be applicable to, for instance, ultra-hard materials as constituents in achieving new damage-resistance composites.

Prediction of compressive strength of the welded matrix-rock mixture by meso-inclusion theory

As a special and widely distributed geological material, the matrix-rock mixture (block-in-matrix texture) has been worldwide focused on its complex physical and mechanical properties for 25 years. However, the macro-meso mechanical relationship of matrix-rock mixture has not been well clarified so far, leading to the unclear understanding of its mechanical behavior. In this paper, the welded matrix-rock mixture is considered as a two-phase composite material, and a mesoscopic mechanical method is presented for calculating the uniaxial compressive strength (UCS). The influence of volumetric block proportion of rock (VBP) and mechanical contrast of meso components (i.e. UCS ratio (SR) and modulus ratio (MR) of rock to matrix) on the strength and the failure mechanism of the matrix-rock mixture is illustrated by the meso-inclusion theory. To avoid the rock damage in the welded mixture, it is suggested that the SR of rock to matrix should be larger than 1.5 for the low stiffness ratio of rock to matrix (e.g. MR ≤ 5), while for the mixture with high stiffness contrast (e.g. 5 < MR < 100) the SR of rock to matrix should be larger than 2. For the common case of strong rock-weak matrix mixture, the reinforced effect of VBP is positive with the MR of rock to matrix but seems to be insignificant when MR > 100. Meanwhile, the Weibull function is adopted to describe the strength property of the matrix in view of its strength randomness contributing to the matrix-rock mixture. It is shown that the strength evolution of the mixtures can be effectively predicted by the present model considering the Weibull distributed strength of the matrix, based on the comparison with the published experimental data and the discussion of existed empirical formulas.

Shear Demands of Rock-Socketed Piles Subject to Cyclic Lateral Loading

The determination of internal pile reactions is critical to designing and assessing the structural performance of deep foundations. Internal shear and moment profiles strongly depend on lateral pile-soil interaction, which in turn depends on pile and soil stiffnesses as well as the stiffness contrast between soft and stiff strata, such as occurs at a soil/rock interface. At zones of strong geomaterial stiffness contrast, Winkler-spring-type analyses predict abrupt changes in the internal pile reactions for laterally-loaded foundation elements. In particular, the sudden deamplification of internal moments when transitioning from a soft to stiff layer is accompanied by amplification of pile shear. This “shear spike” can result in bulky transverse reinforcement designs for drilled shaft rock sockets that pose constructability challenges due to reinforcement congestion, increasing the risk of defective concrete on the outside of the cage. This paper presents an experimental research program of three large-scale, instrumented drilled shafts with simulated rock sockets constructed from concrete. Each shaft had a different transverse reinforcement design intended to bound the amplitude of the predicted amplified shear demand, with a particular emphasis on performance of shafts with shear resistance less than the predicted demand and below the code minimum. Test results suggested that the shafts experienced a flexure-dominated failure irrespective of the transverse reinforcement detailing.

Seismic dispersion and attenuation in layered porous rocks with fractures of varying orientations

ABSTRACTWave‐induced fluid flow plays an important role in affecting the seismic dispersion and attenuation of fractured porous rocks. While numerous theoretical models have been proposed for the seismic dispersion and attenuation in fractured porous rocks, most of them neglect the wave‐induced fluid flow resulting from the background anisotropy (e.g. the interlayer fluid flow between different layers) that can be normal in real reservoirs. Here, according to the theories of poroelasticity, we present an approach to study the frequency‐dependent seismic properties of more realistic and complicated rocks, i.e. horizontally and periodically layered porous rock with horizontal and randomly orienting fractures, respectively, distributed in one of the two periodical layers. The approach accounts for the dual effects of the wave‐induced fluid flow between the fractures and the background pores and between different layers (the interlayer fluid flow). Because C33 (i.e., the modulus of the normally incident P‐wave) is directly related to the P‐wave velocity widely measured in the seismic exploration, and its comprehensive dispersion and attenuation are found to be most significant, we study mainly the effects of fracture properties and the stiffness contrast between the different layers on the seismic dispersion and attenuation of C33. The results show that the increasing stiffness contrast enhances the interlayer fluid flow of the layered porous rocks with both horizontal and randomly orienting fractures and weakens the wave‐induced fluid flow between the fractures and the background pores, especially for the layered porous rock with horizontal fractures. The modelling results also demonstrate that for the considered rock construction, the increasing fracture density reduces the interlayer fluid flow while improves the dispersion and attenuation in the fracture‐relevant frequency band. Increasing fracture aspect ratio is found to reduce the dispersion and attenuation in the fracture‐relevant frequency band only, especially for the layered porous rock with horizontal fractures.

Mechanics Based Tomography (MBT): Validation using experimental data

Tomography based imaging is used in various disciplines with the most widely known as computed tomography (CT). In general, they have in common that a signal is measured on the specimen's surface and at multiple locations to reconstruct some type of a material property distribution using application specific constitutive equations. In this paper and for the first time with experimental validation, a novel tomography approach is successfully introduced based on the mechanics of solids. It utilizes the equations of equilibrium at its core embedded in an optimization framework to control the ill-posed nature of these problems. Measured signals are deformation fields obtained from a digital image correlation system with photo cameras. This work demonstrates the potential of mechanics based tomography (MBT) on a composite silicone material. This work encourages to investigate MBT as a breast tumor screening tool to visualize tumors based on their stiffness contrast. Another long-term goal could be to investigate the use of this methodology as a non-destructive testing tool for civil engineering structures such as bridges. Finally, this new methodology could potentially be miniaturized with stereoscopes and extended to map the material property distribution at the microstructure, e.g. grain length-scale.

Seismic performance of two classes of earth dams

AbstractIn the last decades, Italy has experienced several strong earthquakes, triggering the attention on the high seismic risk associated with the potential instability of large existing earth dams. Under intense seismic events, dam response depends on various factors including the geometry and the type of water retention scheme. This paper explores the influence of these factors, comparing the seismic performance of two idealized earth dams: a homogeneous dam and a zoned dam. The simplified models adopted in the analyses are representative of these two classes of earth dams, often adopted in the sixties to design various dams located in southern Italy. The idealized models, here examined in detail, have comparable heights and foundation soil conditions, differing in terms of water retention scheme. The seismic response of the dams was evaluated through time‐domain nonlinear dynamic analyses in which the same input ground motion, represented by real‐time histories, was applied at the base of the models. It is shown that for highly inelastic systems, such as those at hand, duration of input motion should be accounted for in addition to compatibility criteria with a design elastic response spectrum. Also, different slopes of dam flanks, shear strength mobilization at the end of dam construction and high stiffness contrast at the shells‐core contacts are shown to result in different deformation patterns at the end of earthquake loading. Some peculiarities in the behavior of these classes of earth dams are highlighted in the paper, providing a guidance for the rational assessment of their seismic performance.

Seismically Induced Unclogging in Fluid‐Saturated Faults

AbstractEvidence shows that flow‐driven unclogging of pore spaces is correlated with permeability variations in fluid‐saturated porous rocks. Due to the well‐established ability of seismic waves to induce transient fluid flow in porous media, permeability changes due to seismically induced unclogging have been proposed to explain hydrogeological phenomena commonly associated with distant earthquakes. In an effort to demonstrate the effects of seismically induced unclogging, laboratory experiments of forced oscillatory flow in centimeter‐scale samples have been performed. However, the corresponding extrapolation of the observations to the field scale has yet to be addressed. In this work, we model the coupling between the strains imposed by propagating seismic body waves and the development of transient flow in porous media following Biot's theory of poroelasticity. To assess the potential of seismically induced unclogging, we use previously reported flow velocity thresholds for which measurable permeability variations were observed. We show that only diffusive waves can induce flow velocities in the order of those capable of initiating unclogging. In heterogeneous media, diffusive waves are created as energy conversion from passing seismic waves at the interfaces separating two porous phases of the medium. We investigate this mesoscale process for body waves propagating across a fault zone as a function of the energy density, frequency, and incidence angle of the waves. Seismically induced unclogging potential in fault zones increases with frequency and imposed strain, although this relation is strongly affected by the incidence angle of the seismic wave, the fault thickness, and the stiffness contrast between the fault and the embedding background.

Toward Quantitative and Operator-independent Quasi-static Ultrasound Elastography: An Ex Vivo Feasibility Study.

It is known that the elasticity of liver reduces progressively in the case of diffuse liver disease. Currently, the diagnosis of diffuse liver disease requires a biopsy, which is an invasive procedure. In this paper, we evaluate and report a noninvasive method that can be used to quantify liver stiffness using quasi-static ultrasound elastography approach. Quasi-static elastography is popular in clinical applications where the qualitative assessment of relative tissue stiffness is enough, whereas its potential is relatively underutilized in liver imaging due to lack of local stiffness contrast in the case of diffuse liver disease. Recently, we demonstrated an approach of using a calibrated reference layer to produce quantitative modulus elastograms of the target tissue in simulations and phantom experiments. In a separate work, we reported the development of a compact handheld device to reduce inter- and intraoperator variability in freehand elastography. In this work, we have integrated the reference layer with a handheld controlled compression device and evaluate it for quantitative liver stiffness imaging application. The performance of this technique was assessed on ex vivo goat liver samples. The Young's modulus values obtained from indentation measurements of liver samples acted as the ground truth for comparison. The results from this work demonstrate that by combining the handheld device along with reference layer, the estimated Young's modulus value approaches the ground truth with less error compared with that obtained using freehand compression (8% vs. 15%). The results suggest that the intra- and interoperator reproducibility of the liver elasticity also improved when using the handheld device. Elastography with a handheld compression device and reference layer is a reliable and simple technique to provide a quantitative measure of elasticity.

Dyke-arrest scenarios in extensional regimes: Insights from field observations and numerical models, Santorini, Greece

During a volcanic unrest period with magma-chamber rupture, fluid-driven fractures (dykes) are injected either from deep reservoirs or shallow magma chambers. Subsequently, the dykes follow propagation paths towards the surface, some eventually reaching the surface to erupt while others become arrested. Here we study dyke paths resulting in eruption or arrest in an excellent 5-km wide exposure of the northern caldera wall of the Santorini volcano in Greece. Mapping of >90 dyke segments shows that they were emplaced in a host rock consisting of layers (of breccia, tuff, scoria, and lava) with a wide variety of mechanical properties. At the contacts, some dykes are arrested or deflected and hence change their propagation paths. Here we combine the field data with numerical models to explore dyke paths resulting in (1) arrest and (2) eruption. We investigate the effect of different host-rock mechanical properties, magmatic overpressures, and tectonic loading on dyke paths. We find that layers with unfavorable local stresses for dyke propagation, namely stress barriers, result from layer stiffness (Young's modulus) contrast and thickness variations and are a common cause of dyke arrest. The study also shows how the details of the dyke path, and eventually dyke-fed eruptions, depend on the mechanical layering and local stresses in volcanoes. The results are of great importance for understanding dyke-propagation paths, and the likelihood of eruption, during unrest periods, particularly in stratovolcanoes fed by shallow chambers, such as Santorini.

3D printed architected hollow sphere foams with low-frequency phononic band gaps

We experimentally and numerically investigate elastic wave propagation in a class of lightweight architected materials composed of hollow spheres and binders. Elastic wave transmission tests demonstrate the existence of vibration mitigation capability in the proposed architected foams, which is validated against the numerically predicted phononic band gap. We further describe that the phononic band gap properties can be significantly altered through changing hollow sphere thickness and binder size in the architected foams. Importantly, our results indicate that by increasing the stiffness contrast between hollow spheres and binders, the phononic band gaps are broadened and shifted toward a low-frequency range. At the threshold stiffness contrast of 50, the proposed architected foam requires only a volume fraction of 10.8% while exhibiting an omnidirectional band gap size exceeding 130%. The proposed design paradigm and physical mechanisms are robust and applicable to architected foams with other topologies, thus providing new opportunities to design phononic metamaterials for low-frequency vibration control.

The Value of Elasticity Contrast Index in the Differential Diagnosis of Thyroid Solid Nodules.

To assess the clinical value of elasticity contrast index (ECI) in differentiating malignant thyroid nodules from benign ones. Conventional ultrasound and elastography with pulsation of the carotid artery used as the compression source were retrospectively reviewed on 175 patients (143 females and 32 males; mean ± SD age, 45.17 ± 11.45 years) with 236 solid nodules (113 malignant and 123 benign). All nodules were confirmed by fine-needle aspiration or surgery to be accurately diagnosed. Elasticity contrast index values were computed and used to quantify local stiffness contrast within a nodule as determined with elastography. Elasticity contrast index values between the malignant and benign groups were compared and then related with pathological results. Diagnostic performance of this method was evaluated with use of the receiver operating characteristic curve. Mean ± SD ECI values for malignant thyroid nodules were significantly greater than those for benign nodules (3.67 ± 1.20 vs 1.80 ± 0.74, P < 0.01). Area under the receiver operating characteristic curve of ECI values was 0.907 (95% confidence interval, 0.867-0.948), and the best cutoff point was 2.16, leading to a sensitivity of 90.3%, specificity of 82.9%, positive predictive value of 83.7% and negative predictive value of 91.2%. Elasticity contrast index values can serve as a useful parameter in the differential diagnosis of solid thyroid nodules. With the use of ECI values, objective quantitative information on the tumor stiffness can be achieved to improve diagnostic confidence.