Optimization of a surface wave elastography method through diffraction and guided waves effects characterization

Soft biological tissue elasticity is a parameter whose reliable measure is relevant to many applications in fields as diverse as medicine and the agrifood industry. The ultrasonic elastography methods are often unviable to be applied to provide such solutions. In this way, the surface wave elastography (SWE) appears as a viable alternative, due its low cost, easy to use, non-invasive-destructive character as well as its ability to provide in vivo estimates. Previous studies have described a good correlation between the overall behavior of ultrasonic elastography and SWE, although the latter overestimates the elasticity values compared to the first. It has been suggested that this is due to the influence of certain physical effects related to the exclusive use of low frequency waves, as well as by characteristics of the experimental setup and/or medium. In this work we confirm the influence of such effects and discuss different strategies to make independent the estimations thereof. This allows achieving a good agreement between the ultrasonic reference method and SWE. Thus, SWE becomes a reliable method to estimate soft biological tissue elasticity

Load sharing between synergistic muscles characterized by a ligand‑binding approach and elastography

The skeletal muscle contraction is determined by cross-bridge formation between the myosin heads and the actin active sites. When the muscle contracts, it shortens, increasing its longitudinal shear elastic modulus (µL). Structurally, skeletal muscle can be considered analogous to the molecular receptors that form receptor–ligand complexes and exhibit specifc ligand-binding dynamics. In this context, this work aims to apply elastography and the ligand-binding framework to approach the possible intrinsic mechanisms behind muscle synergism. Based on the short-range stifness principle and the acoustic–elasticity theory, we defne the coefcient C, which is directly related to the fraction saturation of molecular receptors and links the relative longitudinal deformation of the muscle to its µL. We show that such a coefcient can be obtained directly from µL estimates, thus calculating it for the biceps brachii, brachioradialis, and brachialis muscles during isometric elbow fexion torque (τ) ramps. The resulting C(τ ) curves were analyzed by conventional characterization methods of receptor– ligand systems to study the dynamical behavior of each muscle. The results showed that, depending on muscle, C(τ ) exhibits typical ligand-binding dynamics during joint torque production. Therefore, the above indicates that these diferent behaviors describe the longitudinal shortening pattern of each muscle during load sharing. As a plausible interpretation, we suggested that this could be related to the binding kinetics of the cross-bridges during their synergistic action as torque increases. Likewise, it shows that elastography could be useful to assess contractile processes at diferent scales related to the change in the mechanical properties of skeletal muscle.CSIC: No. 004010-000137-2

South American giant short-faced bear (Arctotherium angustidens) diet: evidence from pathology, morphology, stable isotopes, and biomechanics

Fil: Soibelzon, Leopoldo Héctor. División Paleontología Vertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Grinspan, Gustavo A.. Núcleo de Biomecánica. Espacio Interdisciplinario. Universidad de la República. Montevideo; UruguayFil: Bocherens, Hervé. Department of Geosciences. Biogeology. University Tübingen. Tübingen; GermanyFil: Acosta, Walter G.. Cátedra de Semiología. Facultad de Ciencias Veterinarias. Universidad Nacional de La Plata; ArgentinaFil: Jones, Washington. Núcleo de Biomecánica. Espacio Interdisciplinario. Universidad de la República. Montevideo; UruguayFil: Blanco, Ernesto R.. nstituto de Física. Facultad de Ciencias. Universidad de la República. Montevideo; UruguayFil: Prevosti, Francisco. División Mastozoología. Museo Argentino de Ciencias Naturales Bernardino Rivadavia. Buenos Aires; Argentin

Surface wave elastography is a reliable method to correlate muscle elasticity, torque, and electromyography activity level

Abstract The shear elastic modulus is one of the most important parameters to characterize the mechanical behavior of soft tissues. In biomechanics, ultrasound elastography is the gold standard for measuring and mapping it locally in skeletal muscle in vivo. However, their applications are limited to the laboratory or clinic. Thus, low‐frequency elastography methods have recently emerged as a novel alternative to ultrasound elastography. Avoiding the use of high frequencies, these methods allow obtaining a mean value of bulk shear elasticity. However, they are frequently susceptible to diffraction, guided waves, and near field effects, which introduces biases in the estimates. The goal of this work is to test the performance of the non‐ultrasound surface wave elastography (NU‐SWE), which is portable and is based on new algorithms designed to correct the incidence of such effects. Thus, we show its first application to muscle biomechanics. We performed two experiments to assess the relationships of muscle shear elasticity versus joint torque (experiment 1) and the electromyographic activity level (experiment 2). Our results were comparable regarding previous works using the reference ultrasonic methods. Thus, the NU‐SWE showed its potentiality to get wide the biomechanical applications of elastography in many areas of health and sports sciences

Analysis of Rayleigh-Lamb Modes in Soft-solids with Application to Surface Wave Elastography

International audienceThe goal of Surface Wave Elastography (SE) techniques is to estimate the shear elasticity of the sample by measuring the surface wave speed. In SE the thickness of the sample is often assumed to be infinite, in this way, the surface wave speed is directly linked to the sample's shear elasticity. However for many applications this assumption is not true. In this work, we study experimentally the Rayleigh-Lamb modes in soft solids of finite thickness to explore the optimal conditions for SWE. Experiments were carried out in three tissue mimicking phantoms of different thicknesses (10 mm, 20 mm and 60 mm) and same shear elasticity. The surface waves were generated at the surface of the phantom using piston attached to a mechanical vibrator. The central frequency of the excitation was varied between 60 Hz to 160 Hz. One component of the displacement field generated by the piston was measured at the surface and in the bulk of the sample trough a standard speckle tracking technique using a 256 element, 7.5 MHz central frequency linear array and an ultrasound ultrafast electronics. Finally, by measuring the phase velocity at each excitation frequency, velocity dispersion curves were obtained for each phantom. The results show that instead of a Rayleigh wave, zero order symmetric (S 0) and antisymmetric (A 0) Lamb modes are excited with this type of source. Moreover, in this study we show that due to the near field effects of the source, which are appreciable only in soft solids at low frequencies, both Lamb modes are separable in time and space. We show that while the Ao mode dominates close the source, the S 0 mode dominates far away

Table1_Widening the frontiers of elastography in biomechanics: simultaneous muscle elasticity measurements at high-sample rate with surface wave elastography.XLSX

Introduction: In recent years, elastography has become a widely accepted methodology to assess the longitudinal shear elastic modulus of skeletal muscle. Ultrasound shear wave elastography is the gold standard used for such a purpose. However, its low sample rate (1–2 Hz) and the impossibility of being used in several muscles simultaneously limit potential biomechanical applications. In this work, we overcome such limitations by using a surface wave elastography method (NU-SWE).Methods: The NU-SWE comprises a wearable device suitable for measuring several muscles simultaneously. Elasticity can be measured at high-frequency rates (∼15 Hz), by propagating several pulse trains of low-frequency (∼100 Hz) superficial waves separated by a short time interval. These pulses propagate along the medium surface and are recorded by a linear array of vibration sensors placed on the skin of each measured muscle. In this context, this work carried out a proof of concept, showing how NU-SWE enables performing experimental protocols previously impracticable with ultrasound elastography. Thus, we measured the longitudinal shear elasticity of the biceps brachii and brachioradialis muscles simultaneously at 15 Hz during isometric elbow flexions exerted at different torque development rates. Furthermore, for comparison, we measured the electromyographic activity of both muscles.Results: Our results show that the maximum elasticity reached by the brachioradialis increases with contraction rate, while the biceps brachii behaves inversely.Discussion: This study provides new insights concerning muscle synergism, evidenced by changes in muscle elasticity during torque production. More generally, it shows that NU-SWE could help widen elastography-driven research in biomechanics.</p

Table2_Widening the frontiers of elastography in biomechanics: simultaneous muscle elasticity measurements at high-sample rate with surface wave elastography.XLSX

Introduction: In recent years, elastography has become a widely accepted methodology to assess the longitudinal shear elastic modulus of skeletal muscle. Ultrasound shear wave elastography is the gold standard used for such a purpose. However, its low sample rate (1–2 Hz) and the impossibility of being used in several muscles simultaneously limit potential biomechanical applications. In this work, we overcome such limitations by using a surface wave elastography method (NU-SWE).Methods: The NU-SWE comprises a wearable device suitable for measuring several muscles simultaneously. Elasticity can be measured at high-frequency rates (∼15 Hz), by propagating several pulse trains of low-frequency (∼100 Hz) superficial waves separated by a short time interval. These pulses propagate along the medium surface and are recorded by a linear array of vibration sensors placed on the skin of each measured muscle. In this context, this work carried out a proof of concept, showing how NU-SWE enables performing experimental protocols previously impracticable with ultrasound elastography. Thus, we measured the longitudinal shear elasticity of the biceps brachii and brachioradialis muscles simultaneously at 15 Hz during isometric elbow flexions exerted at different torque development rates. Furthermore, for comparison, we measured the electromyographic activity of both muscles.Results: Our results show that the maximum elasticity reached by the brachioradialis increases with contraction rate, while the biceps brachii behaves inversely.Discussion: This study provides new insights concerning muscle synergism, evidenced by changes in muscle elasticity during torque production. More generally, it shows that NU-SWE could help widen elastography-driven research in biomechanics.</p

Informe final del proyecto: Elastografía para la evaluación clínica de tejidos anisotrópicos y visco-elásticos

La elastografía es una nueva modalidad de imagenología médica que mide de forma no invasiva la rigidez de tejidos blandos pudiendo aportar nueva información para la valoración del músculo. La elastografía consiste en la generación de una onda de cizalla para a partir de su propagación medir la elasticidad del tejido. Si bien actualmente varios ecógrafos comerciales cuentan con elastografía, su aplicación al sistema músculo-esquelético se encuentra limitada por las hipótesis del problema: los músculos son anisotrópicos y visco-elásticos. Este proyecto básico-clínico tuvo como objetivo general extender los límites de aplicabilidad de la elastografía y dar un primer paso hacia la introducción de la misma en la clínica nacional, ya que su uso es incipiente en Uruguay. Particularmente se propuso una nueva forma de medida de la atenuación de la onda de cizalla en músculo, estando la atenuación íntimamente relacionada con la viscosidad del tejido. Además se trabajó sobre un nuevo tipo de secuencia ultrasónica mediante la cual fue posible medir el factor de anisotropía del músculo tanto en módulo de cizalla como en módulo de Young. En cuanto a la aplicación clínica, se desarrolló un protocolo de medida confiable para elastografía en miembros inferiores para los músculos bíceps femoral y recto anterior del cuádriceps (Tesis de Maestría Vera De Mora). También se desarrolló un prototipo de Elastografía por Onda de Superficie y su correspondiente protocolo para uso clínico (Tesis Doctorado Gustavo Grinspan), validándose su uso en músculos de miembros inferiores. Para llevar adelante el proyecto se adquirió un ecógrafo, único en el país, modelo Aixplorer V12 (SuperSonic Imagine) referencia en elastografía MSK. Los resultados científicos incorporando nuevos parámetros a la elastografía y protocolización, el equipamiento adquirido y la formación de recursos humanos especializados son los principales aportes de este proyecto, consolidando esta línea de trabajo interdisciplinar.Agencia Nacional de Investigación e Innovació