Ultrasound imaging as a tool to track joint kinematics across persons with varying muscle sizes

Authors

• SM Patwardhan
• JS Schofield
• WMJ Joiner
• TC Bulea
• S Sikdar

Abstract

Sonomyography measures muscle deformation with ultrasound. The extracted signals can be used to proportionally control a device. Although point-to-point reaching movements in healthy individuals are known to follow a minimum jerk trajectory, it is unknown if muscle activation follows a similar control policy. To test this, we performed an experiment (10 subjects) in which seven virtual targets (five trials each) were presented on a screen. Subjects were asked to acquire these virtual targets by flexing/extending their wrist, that in turn drove a virtual cursor left/right based on the extent of flexion/extension measured by sonomyography. To assess potential feasibility in individuals with neurological disorders that result in reduced muscle volume, we examined how differences in muscle size affect the control relationships and the ability of ultrasound to capture them. Muscle thickness was defined as the distance between the superficial adipose tissue-muscle interface and the muscle-bone interface. Velocity profiles derived from imaging muscle activation during target acquisition followed a minimum jerk trajectory. Average muscle thickness across subjects was 3.35±0.44 cm. Target acquisition results showed very low average standard deviation in position traces across trials (4.4%). These current results show that sonomyography can track muscle kinematics to reveal the common minimum jerk trajectory control policy in real-time across a group with varying muscle thickness. These findings support the use of sonomyograpy to characterize muscle contraction trajectories in individuals with upper-neuromotor pathology, such as stroke or cerebral palsy, which could reveal whether their isolated muscle contractions follow similar control policies.

Scientific Focus Area: Neuroscience

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