Neckline-free open-source cap design and improved motion resistance for perioperative fNIRS procedures

Functional near-infrared spectroscopy (fNIRS) caps are limited by motion artifacts and unstable optode-scalp coupling, which degrade signal quality during extended and naturalistic monitoring sessions. We present a fabric-based, chinstrap-free headcap designed to improve mechanical stability and optical signal fidelity through enhanced coupling and reduced relative motion. The open-source cap incorporates a two-layer design with slip-resistant materials and a circumferential tightening mechanism. Performance was evaluated over a two-hour protocol in a mock operating room environment, with motion quantified via image-based tracking, signal quality assessed using signal-to-noise ratio (SNR), scalp-coupling index (SCI), and breath-holding responses, and user comfort evaluated with a human factors questionnaire. Results show reduced displacement and robust hemodynamic signals, supporting improved reliability of fNIRS measurements in perioperative conditions.