Limitations of Muscle Ultrasound Shear Wave Elastography for Clinical Routine-Positioning and Muscle Selection.

Alyssa Romano,Justus Marquetand,Cornelius Kronlage,Deborah Staber,Alexander Grimm

doi:10.3390/s21248490

Abstract

Shear wave elastography (SWE) is a clinical ultrasound imaging modality that enables non-invasive estimation of tissue elasticity. However, various methodological factors—such as vendor-specific implementations of SWE, mechanical anisotropy of tissue, varying anatomical position of muscle and changes in elasticity due to passive muscle stretch—can confound muscle SWE measurements and increase their variability. A measurement protocol with a low variability of reference measurements in healthy subjects is desirable to facilitate diagnostic conclusions on an individual-patient level. Here, we present data from 52 healthy volunteers in the areas of: (1) Characterizing different limb and truncal muscles in terms of inter-subject variability of SWE measurements. Superficial muscles with little pennation, such as biceps brachii, exhibit the lowest variability whereas paravertebral muscles show the highest. (2) Comparing two protocols with different limb positioning in a trade-off between examination convenience and SWE measurement variability. Repositioning to achieve low passive extension of each muscle results in the lowest SWE variability. (3) Providing SWE shear wave velocity (SWV) reference values for a specific ultrasound machine/transducer setup (Canon Aplio i800, 18 MHz probe) for a number of muscles and two positioning protocols. We argue that methodological issues limit the current clinical applicability of muscle SWE.

Highlights

Shear wave elastography (SWE) is a specialized modality in ultrasound imaging that allows the measurement of elasticity, or stiffness, of various bodily tissues
Group-level differences in muscle SWE for at least some muscles in comparison to healthy controls have been demonstrated for Duchenne muscular dystrophy [7,8] as well as inflammatory myopathies [9]; a correlation of muscle elasticity as determined by SWE with muscle strength has been described in inclusion-body myositis [10]; muscle SWE has been shown to resolve delayed muscle relaxation in myotonic muscle disorders [11]
In group-level comparisons, muscle elasticity as determined by ultrasound SWE has been found to be altered in different myopathies [7,8,10], e.g., elasticity is likely reduced in idiopathic inflammatory myopathies (IIM) when compared to healthy controls [24,25]

Summary

Introduction

Shear wave elastography (SWE) is a specialized modality in ultrasound imaging that allows the measurement of elasticity, or stiffness, of various bodily tissues. Elasticity can be estimated from shear wave velocity (SWV), assuming a linear elastic, isotropic and homogenous tissue model, using the equation for shear elastic modulus (μ), where μ = ρVs2 [2]. In this equation, ρ represents the density of the examined tissue (ρ for muscle can be estimated to be 1000 kg/m3) and Vs denotes the SWV. An increase in shear elastic modulus, or stiffness, is positively correlated with an increase in SWV [3]. Group-level differences in muscle SWE for at least some muscles in comparison to healthy controls have been demonstrated for Duchenne muscular dystrophy [7,8] as well as inflammatory myopathies [9]; a correlation of muscle elasticity as determined by SWE with muscle strength has been described in inclusion-body myositis [10]; muscle SWE has been shown to resolve delayed muscle relaxation in myotonic muscle disorders [11]

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