Simulation of Near-Infrared Light Absorption Considering Individual Head and Prefrontal Cortex Anatomy: Implications for Optical Neuroimaging

Functional near-infrared spectroscopy (fNIRS) is an established optical neuroimaging method for measuring functional hemodynamic responses to infer neural activation. However, the impact of individual anatomy on the sensitivity of fNIRS measuring hemodynamics within cortical gray matter is still unknown. By means of Monte Carlo simulations and structural MRI of 23 healthy subjects (mean age: [Image: see text] years), we characterized the individual distribution of tissue-specific NIR-light absorption underneath 24 prefrontal fNIRS channels. We, thereby, investigated the impact of scalp-cortex distance (SCD), frontal sinus volume as well as sulcal morphology on gray matter volumes ([Image: see text]) traversed by NIR-light, i.e. anatomy-dependent fNIRS sensitivity. The NIR-light absorption between optodes was distributed describing a rotational ellipsoid with a mean penetration depth of [Image: see text] considering the deepest [Image: see text] of light. Of the detected photon packages scalp and bone absorbed [Image: see text] and [Image: see text] absorbed [Image: see text] of the energy. The mean [Image: see text] volume [Image: see text] was negatively correlated ([Image: see text]) with the SCD and frontal sinus volume ([Image: see text]) and was reduced by [Image: see text] in subjects with relatively large compared to small frontal sinus. Head circumference was significantly positively correlated with the mean SCD ([Image: see text]) and the traversed frontal sinus volume ([Image: see text]). Sulcal morphology had no significant impact on [Image: see text]. Our findings suggest to consider individual SCD and frontal sinus volume as anatomical factors impacting fNIRS sensitivity. Head circumference may represent a practical measure to partly control for these sources of error variance.