Facial magnetomyography using an array of optically pumped magnetometers.

Objective: Measuring facial muscle activity is crucial in the diagnosis of facial palsy. This study investigated whether contactless Magnetomyography (MMG) using optically pumped magnetometers (OPM) is feasible for visualizing facial muscle activity. Methods: An anatomically shaped mask featuring eleven OPM was arranged on one side of the face of five healthy subjects. MMG was recorded while they performed different facial expressions. The root mean square of each OPM signal was calculated for each expression and subject and allocated to the individual face. Moreover, the maximum average muscle activity and the signal-to-noise ratio (SNR) were determined. Results: The subjects' facial muscle activity could be measured individually per facial expression. Mean RMS was 0.6pT (SD 0.4pT), resulting in a mean SNR of 2.2 (SD 1.2). Conclusions: Imaging facial activity via MMG using OPM is possible, although the sensor positioning (sensor geometry and distance to the muscle) is decisive. However, the signal amplitude of the facial muscles is low and the interindividual anatomical variability renders the measurement setup challenging. Significance: As the imaging of facial MMG is feasible, this study paves the way for future studies using OPM for the diagnosis, monitoring, and rehabilitation of facial muscle and facial nerve disorders.