# Wide-Based Illumination and Detection in Functional Near-Infrared Spectroscopy for Enhanced Seizure Detection in Grey Matter

## TL;DR

This study improves fNIRS for epilepsy monitoring by using wider optodes and increased spacing to better detect brain activity and reduce scalp interference.

## Contribution

The study introduces wide-based optodes and increased emitter–detector separation to enhance fNIRS sensitivity for seizure detection.

## Key findings

- Increasing optode diameters and separation improved signal strength and reduced scalp contamination.
- Sensitivity to superficial grey matter changes tripled at 50 mm emitter–detector separation.
- Deep cortical hemodynamic sensitivity also improved with the new setup.

## Abstract

Functional near-infrared spectroscopy (fNIRS) is a non-invasive method for monitoring brain activity by detecting hemodynamic changes. Studies have shown that it can identify ictal and pre-ictal hemodynamic variations, supporting its potential use as a complement to electroencephalography (EEG) in epilepsy monitoring. This study explores an expanded illumination and detection approach utilizing wide-based optodes and increased emitter–detector separation (EDS) to enhance fNIRS sensitivity to cortical hemodynamic changes while minimizing scalp contamination. A Monte Carlo simulation was designed to assess signal amplitude and sensitivity of fNIRS with varying emitter and detector diameters (1–15 mm) and EDS (30–50 mm). Signal strength, grey matter to scalp path ratio (GSPR), and percentage signal change per absorption coefficients (AC) variation were analyzed. Sensitivity to changes in AC of superficial and deep grey matter (SGM, DGM) and scalp was assessed. Increasing emitter and detector diameters substantially increased total detected photon packet weights, enabling practical use at larger EDS. Sensitivity to SGM AC changes tripled at 50 mm EDS, while GSPR increased by 80%, indicating reduced signal contamination from the scalp. Sensitivity to deep cortical hemodynamic changes also improved. Therefore, wide-based fNIRS optodes with increased EDS can enhance seizure-related hemodynamic detection, potentially improving epilepsy diagnostics.