Guide for wavelength selection of LEDs for fNIRS systems

The usage of functional near-infrared spectroscopy (fNIRS) for monitoring neural activity has increased, and many attempts to build fNIRS systems have been made. For custom made continuous-wave fNIRS systems, selection of the light source plays a critical role in the fNIRS blood-oxygen-level-dependent (BOLD) signal quality. This research has identified three inevitable center wavelength dependent errors caused during the modified Beer-Lambert law (MBLL) process, the process of converting detected light intensity to BOLD signals, for typical light sources and has conducted a series of simulations to identify appropriate center wavelengths with minimal errors. By selecting light sources with center wavelengths within the recommended range, custom continuous-wave fNIRS systems robust against errors can be built.