Measuring anisotropic muscle stiffness properties using elastography

Abstract

Physiological and pathological changes to the anisotropic mechanical properties of skeletal muscle are still largely unknown, with only a few studies quantifying changes in vivo. This study used the noninvasive MR elastography (MRE) technique, in combination with diffusion tensor imaging (DTI), to measure shear modulus anisotropy in the human skeletal muscle in the lower leg. Shear modulus measurements parallel and perpendicular to the fibre direction were made in 10 healthy subjects in the medial gastrocnemius, soleus and tibialis anterior muscles. The results showed significant differences in the medial gastrocnemius (μ‖ = 0.86 ± 0.15 kPa; μ⊥ = 0.66 ± 0.19 kPa, P < 0.001), soleus (μ‖ = 0.83 ± 0.22 kPa; μ⊥ = 0.65 ± 0.13 kPa, P < 0.001) and the tibialis anterior (μ‖ = 0.78 ± 0.24 kPa; μ⊥ = 0.66 ± 0.16 kPa, P = 0.03) muscles, where the shear modulus measured in the direction parallel is greater than that measured in the direction perpendicular to the muscle fibres. No significant differences were measured across muscle groups. This study provides the first direct estimates of the anisotropic shear modulus in the triceps surae muscle group, and shows that the technique may be useful for the probing of mechanical anisotropy changes caused by disease, aging and injury.

Three‐parameter shear wave inversion in MR elastography of incompressible transverse isotropic media: Application to in vivo lower leg muscles

“…Of note, the curl-operator accounts for the directionality of shear waves by separating those curl components related to all three TI material parameters m In this way, Equation [13] includes the directional filters, which are applied separately otherwise (20,24). It is encouraging that the ratio between the shear moduli parallel and perpendicular to the fiber direction reported in a study combining MRE and DTI by Green et al (21) are similar to our ratios m More studies are warranted on the interaction of anisotropic viscoelasticity parameters with muscle load as well as on the observed laterality. Muscle load should be imposed uniformly over the full scan time using a loading apparatus such as that proposed by Ringleb et al (12).…”

Observation of direction-dependent mechanical properties in the human brain with multi-excitation MR elastography

“…Previous anisotropic methods have aimed to reconstruct direction-dependent mechanical properties from a single deformation field through the incorporation of prior knowledge of material symmetry [11, 12, 14, 15, 17]. While the results from these methods appear promising [13, 22, 44], they may suffer in characterizing the heterogeneous anisotropy of the human brain if the excited shear mode is not judiciously chosen to account for material symmetries and sensitive to the material complex properties. By incorporating multiple excitation fields with sensitivities, anisotropic inversions may be stabilized during the reconstruction of multiple material constants.…”

Magnetic resonance elastography of slow and fast shear waves illuminates differences in shear and tensile moduli in anisotropic tissue

“…Such studies have been performed by Sinkus et al (2005) (breast tissue); Green et al (2013), Klatt et al (2010b), Papazoglou et al (2006), Qin et al (2014, 2013) (muscle tissue); Qin et al (2013) (anisotropic phantoms); and Namani et al (2009) (aligned fibrin gels). MRE can also be used to estimate three parameters for ITI material models (Feng et al, 2013b; Guo et al, 2015) and five parameters for general TI material models, or more for general orthotropic models (Romano et al, 2012).…”