Statistical mapping of the effect of knee extension on thigh muscle viscoelastic properties using magnetic resonance elastography

Abstract

Skeletal muscle viscoelastic properties reflect muscle microstructure and neuromuscular activation. Elastographic methods, including magnetic resonance elastography, have been used to characterize muscle viscoelastic properties in terms of region of interest (ROI) measurements. The present study extended this approach to create thresholded pixel-by-pixel maps of viscoelastic properties of skeletal muscle during rest and knee extension in eleven subjects. ROI measurements were taken for individual quadricep muscles and the quadriceps region as a whole, and the viscoelastic parameter map pixels were statistically tested at positive false discovery rate q ≤ 0.25. ROI measurements showed significant (p ≤ 0.05) increase in storage modulus (G') and loss modulus (G″), with G″ increasing more than G', in agreement with previous findings. The q-value maps further identified the vastus intermedius as the primary driver of this change, with greater G″/G' increase than surrounding regions. Additionally, a cluster of significant decrease in G″/G' was found in the region of vastus lateralis below the fulcrum point of the lift. Viscoelastic parameter mapping of contracted muscle allows new insight into the relationship between physiology, neuromuscular activation, and human performance.

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

“…It is worth noting however, that measurements of both |G * | and φ in this study were very similar to measurements that have been made in vivo [23,28,1]. Furthermore, visual comparison of the elastograms produced in silico here with those produced in previous in vivo studies was very favourable.…”

“…The elastograms created from the datasets in this study bear strong resemblance to those obtained in vivo, notably the artefacts associated with aliasing at the boundaries in the φ elastograms and the definition of individual muscles in the |G * | elastograms [1,12]. Importantly, definition remained good at noise levels below 5%; estimations in [12] demonstrated that noise for in vivo MRE of the leg was in the region of 2%.…”

“…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].…”

“…Material properties of the human leg vary through natural physiological processes, such as muscle contraction [1] and aging [2], and through disease states, such as myofascial pain syndrome [3]. A non-invasive method of measuring such properties in vivo is magnetic resonance elastography (MRE).…”

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.…”