Multichannel wearable fNIRS-EEG system for long-term clinical monitoring

Abstract

Continuous brain imaging techniques can be beneficial for the monitoring of neurological pathologies (such as epilepsy or stroke) and neuroimaging protocols involving movement. Among existing ones, functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG) have the advantage of being noninvasive, nonobstructive, inexpensive, yield portable solutions, and offer complementary monitoring of electrical and local hemodynamic activities. This article presents a novel system with 128 fNIRS channels and 32 EEG channels with the potential to cover a larger fraction of the adult superficial cortex than earlier works, is integrated with 32 EEG channels, is light and battery-powered to improve portability, and can transmit data wirelessly to an interface for real-time display of electrical and hemodynamic activities. A novel fNIRS-EEG stretchable cap, two analog channels for auxiliary data (e.g., electrocardiogram), eight digital triggers for event-related protocols and an internal accelerometer for movement artifacts removal contribute to improve data acquisition quality. The system can run continuously for 24 h. Following instrumentation validation and reliability on a solid phantom, performance was evaluated on (1) 12 healthy participants during either a visual (checkerboard) task at rest or while pedalling on a stationary bicycle or a cognitive (language) task and (2) 4 patients admitted either to the epilepsy (n = 3) or stroke (n = 1) units. Data analysis confirmed expected hemodynamic variations during validation recordings and useful clinical information during in-hospital testing. To the best of our knowledge, this is the first demonstration of a wearable wireless multichannel fNIRS-EEG monitoring system in patients with neurological conditions. Hum Brain Mapp 39:7-23, 2018. © 2017 Wiley Periodicals, Inc.

Keywords: cerebral hemodynamics; electroencephalography; epilepsy; functional brain imaging and monitoring; limb-shaking transient ischemic attacks; portable near-infrared spectroscopy.

Figure 1

NIRS‐EEG prototype parts including fNIRS‐EEG caps (A), control module (B), double optodes to gather signal from superficial layers (C), and optode design (D). Spatial sensitivity profile generated with AtlasViewer [Aasted et al. 2015] for each measurement channel for the visual (top) and language (bottom) task (E). Yellow arrow shows the integration of EEG electrodes between NIRS sockets (red arrows). Opening (wholes) in the cap (green arrows) allow better removal of dense long hair.

Figure 2

Global architecture of NIRS‐EEG prototype.

Figure 3

Channel layout and description of the visual paradigm (A). P100 time course and topography over the visual cortex averaged along every stimulation blocks while sitting still (upper row) and pedaling (bottom row) for participant B4. Black line/dot: Neuroscan system. Red line/dot: fNIRS‐EEG prototype (B). Results from the Bland–Altman analysis for the P₁₀₀ amplitude changes at rest (left) and while pedaling (right) between our prototype and Neuroscan. Doted red line: limits of agreement. Solid blue line: bias (C). Δ[HbO₂] (red line)/Δ[Hb] (blue line) time courses over the visual cortex and Δ[HbO₂] topography (15 s), with color‐coded t value after Bonferroni‐correction for multiple comparison (P < 0.0004), averaged over 8 visual stimulation periods in subject B4 obtained from 5 channels over the visual cortex while sitting still (upper row) and pedaling (bottom row). Red and blue shaded area: standard error of the mean for Δ[HbO₂] and Δ[Hb], respectively. Green shaded area: stimulation period (D). Average P100 time course from all 8 participants obtained with our system (solid red line) and the Neuroscan system (solid black line) while sitting still (first row) and pedalling (second row) (E).

Figure 4

Channel layout and description of the language paradigm (A). Δ[HbO₂] topography (15 s), with color‐coded t value after Bonferroni correction, and Δ[HbO₂] (straight line)/Δ[Hb] (dotted line) time courses over the Broca area along all stimulation blocks during the listening task in subject L3 and results from the linear regression and Bland–Altman analysis for Δ[HbO₂] (B). Δ [HbO₂] topography (15 s), with color‐coded t value after Bonferroni correction, and Δ[HbO₂] (straight line)/Δ[Hb] (dotted line) traces over the Wernicke area averaged along all stimulation blocks during the naming task in the same subject and results from the linear regression and Bland–Altman analysis for Δ[HbO₂] (C). Black dot/first row: ISS system. Red dot/second row: fNIRS‐EEG prototype. Left side: blue line. Right side: red line. Doted red line: limits of agreement. Solid blue line: bias.