Viscoelasticity-based MR elastography of skeletal muscle

Abstract

An in vivo multifrequency magnetic resonance elastography (MRE) protocol was developed for studying the viscoelastic properties of human skeletal muscle in different states of contraction. Low-frequency shear vibrations in the range of 25-62.5 Hz were synchronously induced into the femoral muscles of seven volunteers and measured in a cross-sectional view by encoding the fast-transverse shear wave component parallel to the muscle fibers. The so-called springpot model was used for deriving two viscoelastic constants, μ and α, from the dispersion functions of the complex shear modulus in relaxed and in loaded muscle. Representing the shear elasticity parallel to the muscle fibers, μ increased in all volunteers upon contraction from 2.68 ± 0.23 kPa to 3.87 ± 0.50 kPa. Also α varied with load, indicating a change in the geometry of the mechanical network of muscle from relaxation (α = 0.253 ± 0.009) to contraction (α = 0.270 ± 0.009). These results provide a reference for a future assessment of muscular dysfunction using rheological parameters.

MR elastography measurement of the effect of passive warmup prior to eccentric exercise on thigh muscle mechanical properties

“…Other studies using similar techniques include Klatt et al,33 and Barnhill et al,34 who reported values for the storage modulus (i.e., G′ ) in the ranges of 0.7 to 2 kPa, and 1.0 to 1.9 kPa, respectively. These data, however, refer to a single frequency acquisition.…”

“…The actuator was designed at the MRE Research Laboratory, Charité‐Universitätsmedizin Berlin, Germany33 and was firmly secured around the leg using Velcro straps to ensure sufficient wave transmission. A cod liver oil capsule was placed on the actuator to facilitate image plane positioning, which was prescribed 2 cm above the proximal actuator edge to avoid potential effects of compression of the muscle by the actuator ring 45.…”

Finite element analysis to investigate variability of MR elastography in the human thigh

“…This was seen as representative of the circular ring actuator that is often used for inducing vibrations into the leg [22,1]. Frequencies of 25, 37.5, 50 and 62.5 Hz were applied [22,12].…”

“…The model parameters for the biceps, gracilis, semitendinosus and semimembranosus muscles were calculated in the aforementioned Chakouch study and have been utilised here. [22] calculated storage and loss modulus values at multiple frequencies for the grouped quadricep muscles (rectus femoris, vastus medialis, vastus intermedius and vastus lateralis). Parameters for the Zener model based on these measurements were calculated by minimising the cost function in the same manner as previous studies [24,23]:…”

“…There are currently a limited number of studies that have investigated material properties in the leg at the frequency range of interest, and those that have, often typically investigate at a single frequency [1,25] or studied a limited number of muscles within the leg [22,29]. Further work to characterise all the material properties in the human leg and match them to a material model in the same manner as undertaken by [23] would be of considerable benefit to future studies that are similar to the present one.…”