Optics and Photonics Society of Iran

Functional near infrared spectroscopy (fNIRS) is a noninvasive, safe and portable optical imaging modality which can be used to study neural-related hemodynamic signals of brain by measuring concentration changes of Hb and HbO₂. By investigating the optical path length of detected photons in each brain layer, optical density changes due to each layer can be measured for different source-detector separations. In this study, we obtain the sensitivity of fNIRS device to changes of absorption in cortex layer for a five-layer slab brain model and find the optimum source-detector separation. The results show that for absorption changes in cortex layer (at depth of 1 cm), the optimum distance is between 25 mm and 40 mm.