Tracking Muscle Deformation using Ultrasound Imaging During Functional Electrical Stimulation

Authors

• SM Patwardhan
• KE Alter
• JA Stowers
• DL Damiano
• TC Bulea

Abstract

Hybrid robotic exoskeletons use functional electrical stimulation (FES) alongside robotic assistance to provide gait training and rehabilitation to individuals affected with gait pathologies such as cerebral palsy. This requires adjustment of the FES parameters in real-time to enable closed-loop control. However, more information beyond surface electromyography (sEMG) is needed to provide effective closed-loop control of stimulation parameters and improve the quality of movement co-driven by FES. Recent work has shown the utility of ultrasound imaging of the musculature as a human machine interface. This method has an advantage over sEMG because ultrasound imaging captures mechanical deformation of the muscle rather than its electrical activation, thereby potentially reducing the interference of the FES. In this work, we use a simple image similarity metric to compute the extent of muscle deformation using ultrasound imaging, and investigate if ultrasound imaging can be used to track joint kinematics in the presence and absence of FES. We recruited one healthy participant to evaluate our proposed method. The participant performed flexion/extension movements of three joints - wrist, ankle, and knee. We recorded kinematics using motion capture, muscle activity using sEMG, and muscle contraction patterns using ultrasound imaging. We found that the signal extracted from ultrasound imaging tracked joint kinematics with and without FES in the healthy participant with a mean error of 3.9±18.14 for volitional movement and 1.7±20.69% during FES, averaged across all the joints investigated. This study was meant to describe our methods and approach, which we eventually aim to expand to various clinical populations.

Scientific Focus Area: Biomedical Engineering and Biophysics

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