A quantitative measurement method is essentially needed to understand the fundamentals of the musculoskeletal system and develop diagnostic or prognostic strategies, for example, to assess muscle recovery after neurological injuries by quantitatively examining muscle function. Such a method is also preferred to be non-invasive.
Currently, surface electromyography (EMG) is commonly used to measure muscle activity, but it is limited to detecting myoelectric signals without anatomy-associated information. We introduce a new image analysis method, employing ultra-fast ultrasound imaging, to quantify muscle’s spatial-temporal mechanical responses to the external electrical stimulation. The method is based on analyzing the spatial-temporal change of the impulsive kinetic energy during the period of muscle contraction. The analysis can derive an anatomy-registered muscle activation metrics map that allows localizing regions of muscle activation.
To demonstrate our method, in this study, we used electrical stimulation to intentionally evoke regional muscle responses in forearms of five participants without disabilities. We stimulated the median nerve and individual forearm muscle groups, respectively. For each simulation, muscle dynamics due to contractions were recorded simultaneously by two ultrasound probes positioned at 2 different imaging angles. We also synchronously recorded high-density EMG (HD-EMG) signals for comparison.
We presented the ultrasound image-derived activation localization from all five participants. The comparison between ultrasound and HD-EMG measurements indicates a good resemblance for describing muscle recruitment pattern. The proposed ultrasound image-based methodology can potentially become an alternative or complementary approach to surface EMG for the study of skeletal muscle activation and for diagnosis and prognosis in clinical settings.
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