Optical Phantoms for Calibrating a Novel Neuroimaging System Targeting Central Nervous System Fluid Flow Dynamics

Abstract

Fluid flow dynamics in the brain's ventricles, interstitial spaces, and perivascular spaces, known as the “glymphatic system,” are hypothesized to play an important role in brain waste clearance. Healthy function of this complex fluid transporter is most active during sleep, may be critical for maintaining neurological health, and is hypothesized to be important for recovery after acute and chronic injury (e.g. concussion). At present, all sensors for monitoring brain fluid dynamics require invasive contrast agents (e.g. fluorescent dyes injected into cerebrospinal fluid, CSF) and/or are not portable or amenable to long-term repeated monitoring (e.g., magnetic resonance imaging (MRI) methods). We aim to adapt near infrared spectroscopy technologies, which traditionally track hemodynamic activity, to target fluid flow in the glymphatic system and to monitor the temporal dynamics of this water-dominated signal, with an eye toward future applications in continuous portable monitoring. Our goal is to extend frequency domain functional near infrared spectroscopy sensors (FD-fNIRS) to track these CSF-dominated fluid dynamics. In support of this aim, we developed two novel phantoms that mimic key elements of glymphatic system function to demonstrate application of novel FD-fNIRS sensors to human brains in a portable, noninvasive form factor amenable to repeated, continuous testing in a sleep lab-type environment.