Résumé :
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Non-invasive measurements are required for monitoring neuromuscular disorders (NDM) and following the effects of rehabilitation/therapy programs. Since it provides localized elastic modulus (i.e. stiffness) measurements, elastographic methods could be quite valuable for the assessment of individual muscles. In this way, the potential of Magnetic Resonance Elastography (MRE) has already been demonstrated. However, this technique has inherent limitations (e.g. long acquisition time, access difficulties, cost) that might restrict its use in clinical practice. We plan to use a new technique called supersonic shear imaging (SSI), which provides simple, instantaneous and real time measurements. Recent experiments with this technique have shown that the muscle elastic modulus is very sensitive to the muscle state (contraction level, muscle length...), indicating that a very careful standardization is needed to obtain reliable measurements at rest. The aim of this pilot study was to implement a standardized protocol to measure elastic modulus in several muscles using SSI, and to assess the reliability of such measurements.Eight healthy subjects (age ranged from 20 to 26 years) volunteered to participate in the present study. Muscle elastic modulus was measured at rest using an AixPlorer ultrasonic scanner (Supersonic Imagine, Aix en Provence, France) set in the SSI mode. Nine muscles with different architecture and typology were chosen (pinnate/fusiform muscles, slow/fast fibers, cf. Table 1). For each muscle a standardized joints position was chosen in order to ensure that the muscle was relaxed. To take into account the temporal variability, muscle elastic modulus was averaged over 15 measurements performed at 1 Hz. To assess the repeatability and the inter-day reproducibility, the protocol (duration: about 20 min) was repeated twice: i) on the same day with a 15 min rest in between, and ii) on two different days.Both repeatability and reproducibility were good, with coefficient of variation ranged from 3.2% to 8,3% (Table 1). This reliability is better than the reliability reported in the literature using MRE.Additional subjects will perform the same protocol to strengthen the present results, and inter-operator reliability will be also assessed (these results will be depicted in the communication). The next step will be to use this protocol to characterize muscle mechanical properties in patients with various NMD.Grant: Association Franse contre les Myopathies (n_1497)
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