Biomechanical Properties Of Soft Tissues Research Articles

Skin simulants for wound ballistic investigation – an experimental study

Gunshot wound analysis is an important part of medicolegal practice, in both autopsies and examinations of living persons. Well-established and studied simulants exist that exhibit both physical and biomechanical properties of soft-tissues and bones. Current research literature on ballistic wounds focuses on the biomechanical properties of skin simulants. In our extensive experimental study, we tested numerous synthetic and natural materials, regarding their macromorphological bullet impact characteristics, and compared these data with those from real bullet injuries gathered from medicolegal practice. Over thirty varieties of potential skin simulants were shot perpendicularly, and at 45°, at a distance of 10 m and 0.3 m, using full metal jacket (FMJ) projectiles (9 × 19 mm Luger). Simulants included ballistic gelatine at various concentrations, dental silicones with several degrees of hardness, alginates, latex, chamois leather, suture trainers for medical training purposes and various material compound models. In addition to complying to the general requirements for a synthetic simulant, results obtained from dental silicones shore hardness 70 (backed with 20 % by mass gelatine), were especially highly comparable to gunshot entry wounds in skin from real cases. Based on these results, particularly focusing on the macroscopically detectable criteria, we can strongly recommend dental silicone shore hardness 70 as a skin simulant for wound ballistics examinations.

Supershear Rayleigh wave imaging for quantitative assessment of biomechanical properties of brain using air-coupled optical coherence elastography.

Recently, supershear Rayleigh waves (SRWs) have been proposed to characterize the biomechanical properties of soft tissues. The SRWs propagate along the surface of the medium, unlike surface Rayleigh waves, SRWs propagate faster than bulk shear waves. However, their behavior and application in biological tissues is still elusive. In brain tissue elastography, shear waves combined with magnetic resonance elastography or ultrasound elastography are generally used to quantify the shear modulus, but high spatial resolution elasticity assessment in 10 μm scale is still improving. Here, we develop an air-coupled ultrasonic transducer for noncontact excitation of SRWs and Rayleigh waves in brain tissue, use optical coherent elastography (OCE) to detect, and reconstruct the SRW propagation process; in combing with a derived theoretical model of SRWs on a free boundary surface, we quantify the shear modulus of brain tissue with high spatial resolution. We first complete validation experiments using a homogeneous isotropic agar phantom, and the experimental results clearly show the SRW is 1.9649 times faster than the bulk shear waves. Furthermore, the propagation velocity of SRWs in both the frontal and parietal lobe regions of the brain is all 1.87 times faster than the bulk shear wave velocity. Finally, we evaluated the anisotropy in different brain regions, and the medulla oblongata region had the highest anisotropy index. Our study shows that the OCE system using the SRW model is a new potential approach for high-resolution assessment of the biomechanical properties of brain tissue.

MR Elastography With Optimization-Based Phase Unwrapping and Traveling Wave Expansion-Based Neural Network (TWENN).

Magnetic Resonance Elastography (MRE) can characterize biomechanical properties of soft tissue for disease diagnosis and treatment planning. However, complicated wavefields acquired from MRE coupled with noise pose challenges for accurate displacement extraction and modulus estimation. Using optimization-based displacement extraction and Traveling Wave Expansion-based Neural Network (TWENN) modulus estimation, we propose a new pipeline for processing MRE images. An objective function with Dual Data Consistency (Dual-DC) has been used to ensure accurate phase unwrapping and displacement extraction. For the estimation of complex wavenumbers, a complex-valued neural network with displacement covariance as an input has been developed. A model of traveling wave expansion is used to generate training datasets for the network with varying levels of noise. The complex shear modulus map is obtained through fusion of multifrequency and multidirectional data. Validation using brain and liver simulation images demonstrates the practical value of the proposed pipeline, which can estimate the biomechanical properties with minimal root-mean-square errors when compared to state-of-the-art methods. Applications of the proposed method for processing MRE images of phantom, brain, and liver reveal clear anatomical features, robustness to noise, and good generalizability of the pipeline.

Calcification alters the viscoelastic properties of tendon fascicle bundles depending on matrix content.

Tendon fascicle bundles are often used as biological grafts and thus must meet certain quality requirements, such as excluding calcification, which alters the biomechanical properties of soft tissues. In this work, we investigate the influence of early-stage calcification on the mechanical and structural properties of tendon fascicle bundles with varying matrix content. The calcification process was modeled using sample incubation in concentrated simulated body fluid. Mechanical and structural properties were investigated using uniaxial tests with relaxation periods, dynamic mechanical analysis, as well as magnetic resonance imaging and atomic force microscopy. Mechanical tests showed that the initial phase of calcification causes an increase in the elasticity, storage, and loss modulus, as well as a drop in the normalized value of hysteresis. Further calcification of the samples results in decreased modulus of elasticity and a slight increase in the normalized value of hysteresis. Analysis via MRI and scanning electron microscopy showed that incubation alters fibrillar relationships within the tendon structure and the flow of body fluids. In the initial stage of calcification, calcium phosphate crystals are barely visible; however, extending the incubation time for the next 14 days results in the appearance of calcium phosphate crystals within the tendon structure and leads to damage in its structure. Our results show that the calcification process modifies the collagen-matrix relationships and leads to a change in their mechanical properties. These findings will help to understand the pathogenesis of clinical conditions caused by calcification process, leading to the development of effective treatments for these conditions. STATEMENT OF SIGNIFICANCE: This study investigates how calcium mineral deposition in tendons affects their mechanical response and which processes are responsible for this phenomenon. By analyzing the elastic and viscoelastic properties of animal fascicle bundles affected by calcification induced via incubation in concentrated simulated body fluid, the study sheds light on the relationship between structural and biochemical changes in tendons and their altered mechanical response. This understanding is crucial for optimizing tendinopathy treatment and preventing tendon injury. The findings provide insights into the calcification pathway and its resulting changes in the biomechanical behaviors of affected tendons, which have been previously unclear.

G2Φnet: Relating genotype and biomechanical phenotype of tissues with deep learning.

Many genetic mutations adversely affect the structure and function of load-bearing soft tissues, with clinical sequelae often responsible for disability or death. Parallel advances in genetics and histomechanical characterization provide significant insight into these conditions, but there remains a pressing need to integrate such information. We present a novel genotype-to-biomechanical phenotype neural network (G2Φnet) for characterizing and classifying biomechanical properties of soft tissues, which serve as important functional readouts of tissue health or disease. We illustrate the utility of our approach by inferring the nonlinear, genotype-dependent constitutive behavior of the aorta for four mouse models involving defects or deficiencies in extracellular constituents. We show that G2Φnet can infer the biomechanical response while simultaneously ascribing the associated genotype by utilizing limited, noisy, and unstructured experimental data. More broadly, G2Φnet provides a powerful method and a paradigm shift for correlating genotype and biomechanical phenotype quantitatively, promising a better understanding of their interplay in biological tissues.

Viscosity Plane-Wave UltraSound (Vi PLUS) in the Evaluation of Thyroid Gland in Healthy Volunteers-A Preliminary Study.

Viscosity and elasticity represent biomechanical properties of soft tissues that suffer changes during the pathophysiological alterations of the tissue in various conditions. This study aimed to determine average viscosity values for the thyroid gland and to evaluate the potential influences of age, gender and body mass index (BMI), using a recent technique Viscosity Plane-wave UltraSound (Vi PLUS). A total of 85 healthy Caucasian volunteers (56 women and 29 men, median age of 29 years, range 17–81 years) were included in this prospective monocentric study conducted between January 2022 and March 2022. Thyroid viscosity was measured using the SuperSonic MACH 30® Ultrasound system (Aixplorer, SuperSonic Imagine, Aix-en-Provence, France), equipped with a curvilinear C6-IX transducer that allows simultaneous quantification of the viscosity and stiffness. The mean thyroid viscosity measurement value was 2.63 ± 0.47 Pa.s. No statistically significant differences were detected between the left and the right lobes of the thyroid gland. A significant positive correlation was found between thyroid viscosity and elasticity (r = 0.685, p < 0.0001). There was no statistically significant correlation between body mass index (BMI) and thyroid gland viscosity and elasticity values (r = 0.215, p = 0.053; r = 0.106, p = 0.333). No correlation between viscosity and gender was established (p > 0.05). Vi PLUS represents a new and promising ultrasonographic technique that can provide helpful information for evaluating the thyroid parenchyma, similar to elastography. The effect of the potential confounding factors on thyroid viscosity was negligible, except for BMI.

Establishment of Emergency Teaching Model and Optimization of Discrete Dynamic Calculation in Complex Virtual Simulation Environment

Virtual surgery is a typical application of virtual reality technology in the medical field, which can help improve the success rate of surgery and reduce medical costs in various aspects such as medical training, surgery planning, and intraoperative navigation, and is becoming a hot research topic and a frontier subject in the medical field. The establishment of virtual surgery simulation system involves the intersection and penetration of various disciplines, and the research is difficult, and many functional modules are still not perfect. This study focuses on the key technologies in the virtual surgery simulation system, focusing on two core modules, the soft tissue modeling method and the collision detection algorithm, to improve the accuracy of the soft tissue model deformation under the condition of meeting the real-time system. The biomechanical properties of soft tissues are studied, the viscoelastic properties are analyzed, and the viscoelastic theory is used as the basis for soft tissue modeling; the geometric model is established by using a complementary method of surface model and tetrahedral mesh cells, with the surface model covering the outer surface for visual rendering and the tetrahedral mesh cells for skeleton support of the physical model, so that the model has a better visual effect and deformation effect, which enhances the model fidelity that is enhanced by the better visual effect and deformation effect; the soft tissue physical modeling method is summarized and summarized to lay the foundation for soft tissue model optimization. The experimental results show that the bilateral teleoperation system under analog control can give the operator a better haptic sensation (smaller value of input impedance felt by the operator when doing free motion from the robot) while ensuring good positional tracking and force tracking effects. This method solves the problems of collapse distortion and lack of viscoelastic properties of the traditional mass-spring model, and improves the accuracy of model deformation. Based on the improved algorithm, the viscoelastic hybrid filled sphere model of the liver organ is successfully established, which proves that the modeling method is feasible and effective.

Viscoelastic Characterization of Soft Tissue-Mimicking Gelatin Phantoms using Indentation and Magnetic Resonance Elastography.

Characterization of biomechanical properties of soft biological tissues is important to understand the tissue mechanics and explore the biomechanics-related mechanisms of disease, injury, and development. The mechanical testing method is the most straightforward way for tissue characterization and is considered as verification for in vivo measurement. Among the many ex vivo mechanical testing techniques, the indentation test provides a reliable way, especially for samples that are small, hard to fix, and viscoelastic such as brain tissue. Magnetic resonance elastography (MRE) is a clinically used method to measure the biomechanical properties of soft tissues. Based on shear wave propagation in soft tissues recorded using MRE, viscoelastic properties of soft tissues can be estimated in vivo based on wave equation. Here, the viscoelastic properties of gelatin phantoms with two different concentrations were measured by MRE and indentation. The protocols of phantom fabrication, testing, and modulus estimation have been presented.

Intrinsic Mechanical Cues and Their Impact on Stem Cells and Embryogenesis.

Although understanding how soluble cues direct cellular processes revolutionised the study of cell biology in the second half of the 20th century, over the last two decades, new insights into how mechanical cues similarly impact cell fate decisions has gained momentum. During development, extrinsic cues such as fluid flow, shear stress and compressive forces are essential for normal embryogenesis to proceed. Indeed, both adult and embryonic stem cells can respond to applied forces, but they can also detect intrinsic mechanical cues from their surrounding environment, such as the stiffness of the extracellular matrix, which impacts differentiation and morphogenesis. Cells can detect changes in their mechanical environment using cell surface receptors such as integrins and focal adhesions. Moreover, dynamic rearrangements of the cytoskeleton have been identified as a key means by which forces are transmitted from the extracellular matrix to the cell and vice versa. Although we have some understanding of the downstream mechanisms whereby mechanical cues are translated into changes in cell behaviour, many of the signalling pathways remain to be defined. This review discusses the importance of intrinsic mechanical cues on adult cell fate decisions, the emerging roles of cell surface mechano-sensors and the cytoskeleton in enabling cells to sense its microenvironment, and the role of intracellular signalling in translating mechanical cues into transcriptional outputs. In addition, the contribution of mechanical cues to fundamental processes during embryogenesis such as apical constriction and convergent extension is discussed. The continued development of tools to measure the biomechanical properties of soft tissues in vivo is likely to uncover currently underestimated contributions of these cues to adult stem cell fate decisions and embryogenesis, and may inform on regenerative strategies for tissue repair.

2-D Ultrasonic Array-Based Optical Coherence Elastography.

Acoustic radiation force optical coherence elastography (ARF-OCE) has been successfully implemented to characterize the biomechanical properties of soft tissues, such as the cornea and the retina, with high resolution using single-element ultrasonic transducers for ARF excitation. Most currently proposed OCE techniques, such as air puff and ARF, have less capability to control the spatiotemporal information of the induced region of deformation, resulting in limited accuracy and low temporal resolution of the shear wave elasticity imaging. In this study, we propose a new method called 2-D ultrasonic array-based OCE imaging, which combines the advantages of 3-D dynamic electronic steering of the 2-D ultrasonic array and high-resolution optical coherence tomography (OCT). The 3-D steering capability of the 2-D array was first validated using a hydrophone. Then, the combined 2-D ultrasonic array OCE system was calibrated using a homogenous phantom, followed by an experiment on ex vivo rabbit corneal tissue. The results demonstrate that our newly developed 2-D ultrasonic array-based OCE system has the capability to map tissue biomechanical properties accurately, and therefore, has the potential to be a vital diagnostic tool in ophthalmology.

Surface coating and speckling of the human iliotibial tract does not affect its load-deformation properties

Stochastic surface patterns form an important requirement to facilitate digital image correlation and to subsequently quantify material properties of various tissues when loaded and deformed without artefacts arising from material slippage. Depending on the samples’ natural colour, a surface pattern is created by speckling with colour or dye only, or it requires combined surface coating and speckling before to enhance the contrast, to facilitate high-quality data recording for mechanical evaluation. However, it is unclear to date if the colours deployed for coating and speckling do significantly alter the biomechanical properties of soft tissues. The given study investigated the biomechanical properties of 168 human iliotibial tract samples as a model for collagen-rich soft tissues, separated into four groups: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling following a standardized approach of application and data acquisition. The results reveal that elastic modulus, ultimate tensile strength and strain at maximum force of all groups were similar and statistically non-different (p ≥ 0.69). Qualitatively, the speckle patterns revealed increasing contrast differences in the following order: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling. Conclusively, both coating by water- and solvent-based paints, as well as exclusive graphite speckling, did not significantly influence the load-deformation parameters of the here used human iliotibial tract as a model for collagen-rich soft tissues. In consequence, water- and solvent-based coating paints seem equally suitable to coat collagen-rich soft tissues for digital image correlation, resulting in suitable speckle patterns and unbiased data acquisition.

Cross-Sectional Area Measurement Techniques of Soft Tissue: A Literature Review.

Evaluation of the biomechanical properties of soft tissues by measuring the stress–strain relationships has been the focus of numerous investigations. The accuracy of stress depends, in part, upon the determination of the cross‐sectional area (CSA). However, the complex geometry and pliability of soft tissues, especially ligaments and tendons, make it difficult to obtain accurate CSA, and the development of CSA measurement methods of soft tissues continues. Early attempts to determine the CSA of soft tissues include gravimetric method, geometric approximation technique, area micrometer method, and microtomy technique. Since 1990, a series of new methods have emerged, including medical imaging techniques (e.g. magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging (USI)), laser techniques (e.g. the laser micrometer method, the linear laser scanner (LLS) technique, and the laser reflection system (LRS) method), molding techniques, and three‐dimensional (3D) scanning techniques.

Modeling the initial-volume dependent approximate compressibility of porcine liver tissues using a novel volumetric strain energy model

Experimental observations in the open literature indicate that soft tissues are slightly compressible, and this characteristic affects not only their overall elastic response but also their damage evolution and failure mechanism. In this study, we find that the compressibility of liver tissues is also closely related to the initial specimen volume according to the confined compression tests: the samples with smaller initial volume exhibit more compressible behavior compared to the larger ones. To include this initial-volume dependent effect, we developed a novel volumetric strain energy model with two variables, i.e., the bulk modulus and the compressibility factor. A detailed scheme was proposed as well to identify these two parameters, and the relationship between the bulk modulus and the initial volume was clarified. Findings from this study will help to deepen the understanding of the biomechanical properties of soft tissues. Statement of significanceLiver is a highly vascular organ and traditionally assumed to be an incompressible medium. However, through the confined compression tests, we found that the samples with smaller initial volumes exhibit more compressible behavior. Hence, we developed a novel strain energy density model to characterize the initial-volume dependent hyperelastic response, and found that the bulk modulus of liver tissues is positively related to the initial volume. Our results suggest that the compressibility of liver tissues should be considered in the future study of liver biomechanics.

Cutting procedures with improved visual effects and haptic interaction for surgical simulation systems

Background and objectives: Surface rendering and physical models with constant parameters are often employed for cutting procedures in conventional surgical simulators. As a consequence, the internal structures of soft tissues cannot be rendered properly and haptic interaction is unrealistic. In order to improve both the visual and force feedback, a new volumetric geometric model is introduced. Methods: In this paper, we introduce a new volumetric geometric model, for which multidimensional parameters are derived from the gray values to map the color and transparency of the 3D soft tissues. In the meantime, the biomechanical properties of soft tissues are described by a meshless physical model and the model parameters are closely correlated to the multidimensional parameters of the developed volumetric geometric model. As a beneficial result, the force feedback changes according to the physical properties of different soft tissue structures, which reflects better the real-life scenarios during the course of cutting procedures. Results and Conclusions: Simulation results show that both the surface and internal structures of soft tissues can be rendered properly and the boundaries between different tissue structures are visually distinct in incision. The curves of feedback force change according to the different structures of soft tissue, improving haptic interaction. Compared with the conventional cutting model, both visual effect and haptic interaction are improved in the proposed volumetric geometric model.

Effect of Residual and Transformation Choice on Computational Aspects of Biomechanical Parameter Estimation of Soft Tissues.

Several nonlinear and anisotropic constitutive models have been proposed to describe the biomechanical properties of soft tissues, and reliably estimating the unknown parameters in these models using experimental data is an important step towards developing predictive capabilities. However, the effect of parameter estimation technique on the resulting biomechanical parameters remains under-analyzed. Standard off-the-shelf techniques can produce unreliable results where the parameters are not uniquely identified and can vary with the initial guess. In this study, a thorough analysis of parameter estimation techniques on the resulting properties for four multi-parameter invariant-based constitutive models is presented. It was found that linear transformations have no effect on parameter estimation for the presented cases, and nonlinear transforms are necessary for any improvement. A distinct focus is put on the issue of non-convergence, and we propose simple modifications that not only improve the speed of convergence but also avoid convergence to a wrong solution. The proposed modifications are straightforward to implement and can avoid severe problems in the biomechanical analysis. The results also show that including the fiber angle as an unknown in the parameter estimation makes it extremely challenging, where almost all of the formulations and models fail to converge to the true solution. Therefore, until this issue is resolved, a non-mechanical—such as optical—technique for determining the fiber angle is required in conjunction with the planar biaxial test for a robust biomechanical analysis.

Quantitative stiffness of the median nerve, flexor tendons, and flexor retinaculum in the carpal tunnel measured with acoustic radiation force impulse elastography in various wrist and finger positions.

Despite the high prevalence and clinical importance of soft-tissue disorders, objective methods for evaluation of the biomechanical properties of soft tissues are lacking. This study aimed to quantitatively evaluate stiffness, an important biomechanical characteristic of soft tissue, using acoustic radiation force impulse (ARFI) elastography. The shear wave velocity (SWV, m/s) values of soft tissue structures within the carpal tunnel (CT) were measured in various combinations of wrist and finger positions.Twenty-six healthy adults were enrolled in this study. We measured the cross-sectional area of the median nerve (MN) and the SWV values of several structures within the CT at the CT inlet level. Measurement of SWV of the MN, flexor digitorum superficialis (FDS), flexor digitorum profundus (FDP), and transverse carpal ligament (TCL) were conducted in six wrist/finger motion combinations.When the wrist and fingers were in neutral positions (position A), the mean SWV was lowest for the MN (mean ± standard deviation, 2.3 ± 0.5 m/s), followed by the FDS (2.9 ± 0.2), FDP (3.2 ± 0.3), and TCL (3.3 ± 0.4). The SWV was significantly different among the six different wrist/finger positions for all structures (P < .001). However, the MN cross-sectional area was not significantly different (P = .527). The SWV values for the MN, FDS, and FDP increased significantly as the wrist/finger positions the stress on the tendons increased (from position B to F) compared with a neutral position, while the SWV of the TCL was significantly higher for in all positions compared with neutral, except for wrist neutral, finger extension. The SWV values for the MN, FDS, and TCL gradually increased as stress increased.The intra-CT structures are under increased stress during wrist and finger motions than when the hand is in a neutral position. We have used ARFI elastography to gain insight into the pathophysiology of CTS.

Multi-functional Ultrasonic Micro-elastography Imaging System

In clinical decision making, in addition to anatomical information, biomechanical properties of soft tissues may provide additional clues for disease diagnosis. Given the fact that most of diseases are originated from micron sized structures, an elastography imaging system of fine resolution (~100 µm) and deep penetration depth capable of providing both qualitative and quantitative measurements of biomechanical properties is desired. Here, we report a newly developed multi-functional ultrasonic micro-elastography imaging system in which acoustic radiation force impulse imaging (ARFI) and shear wave elasticity imaging (SWEI) are implemented. To accomplish this, the 4.5 MHz/40 MHz transducer were used as the excitation/detection source, respectively. The imaging system was tested with tissue-mimicking phantoms and an ex vivo chicken liver through 2D/3D imaging. The measured lateral/axial elastography resolution and field of view are 223.7 ± 20.1/109.8 ± 6.9 µm and 1.5 mm for ARFI, 543.6 ± 39.3/117.6 ± 8.7 µm and 2 mm for SWEI, respectively. These results demonstrate that the promising capability of this high resolution elastography imaging system for characterizing tissue biomechanical properties at microscale level and its translational potential into clinical practice.

Elastography: Applications in Peripheral Nerves

The biomechanical properties of soft tissues reflect to some degree the pathophysiology of musculoskeletal disorders. Conventional gray-scale sonography has been widely used as a first-line approach for musculoskeletal disorders because of the advantage of real-time access. Sonoelastography, which we refer to here as strain elastography (SE), requires manual compression vibration and is a modality for quantitatively measuring the elasticity of soft tissue through conventional gray-scale sonography with estimated Young’s modulus or semi-quantitative values as strain ratios. By using the semi-quantitative values of strain ratios, SE has demonstrated promising preliminary results for the diagnosis of masses of the liver, breast, pancreas, prostate, and thyroid, with defined cutoff values. In peripheral nerve disorders, SE could be preferable in clinical practice for detecting the biomechanical changes of tendons, muscles, and ligaments surrounding the nerve, to diagnose and plan preoperational or interventional management. Recently, by using SE, several studies have provided insight into the biomechanical properties and pathophysiological changes associated with entrapment neuropathy as typified by carpal tunnel syndrome. In this presentation, the current knowledge of sonoelastographic techniques and their use for peripheral nerve disorders will be reviewed.

Quantifying tissue viscoelasticity using optical coherence elastography and the Rayleigh wave model.

This study demonstrates the feasibility of using the Rayleigh wave model (RWM) in combination with optical coherence elastography (OCE) technique to assess the viscoelasticity of soft tissues. Dispersion curves calculated from the spectral decomposition of OCE-measured air-pulse induced elastic waves were used to quantify the viscoelasticity of samples using the RWM. Validation studies were first conducted on 10% gelatin phantoms with different concentrations of oil. The results showed that the oil increased the viscosity of the gelatin phantom samples. This method was then used to quantify the viscoelasticity of chicken liver. The Young’s modulus of the chicken liver tissues was estimated as E=2.04±0.88??kPa with a shear viscosity ?=1.20±0.13??Pa?s. The analytical solution of the RWM correlated very well with the OCE-measured phased velocities (R2=0.96±0.04). The results show that the combination of the RWM and OCE is a promising method for noninvasively quantifying the biomechanical properties of soft tissues and may be a useful tool for detecting disease.

General review of magnetic resonance elastography.

Magnetic resonance elastography (MRE) is an innovative imaging technique for the non-invasive quantification of the biomechanical properties of soft tissues via the direct visualization of propagating shear waves in vivo using a modified phase-contrast magnetic resonance imaging (MRI) sequence. Fundamentally, MRE employs the same physical property that physicians utilize when performing manual palpation - that healthy and diseased tissues can be differentiated on the basis of widely differing mechanical stiffness. By performing "virtual palpation", MRE is able to provide information that is beyond the capabilities of conventional morphologic imaging modalities. In an era of increasing adoption of multi-parametric imaging approaches for solving complex problems, MRE can be seamlessly incorporated into a standard MRI examination to provide a rapid, reliable and comprehensive imaging evaluation at a single patient appointment. Originally described by the Mayo Clinic in 1995, the technique represents the most accurate non-invasive method for the detection and staging of liver fibrosis and is currently performed in more than 100 centers worldwide. In this general review, the mechanical properties of soft tissues, principles of MRE, clinical applications of MRE in the liver and beyond, and limitations and future directions of this discipline -are discussed. Selected diagrams and images are provided for illustration.