Partial optical path length in the scalp in subject-specific head models for multi-distance probe configuration of near infrared spectroscopy

In the brain function measurement by near infrared spectroscopy using a multi-distance probe configuration, the ratio of the partial optical path length in the scalp for the long spacing probe pair to that for the short spacing probe pair is important for the calculation to eliminate the scalp component in the signal. Light propagation in the subject specific head models of 45 volunteers was calculated to predict the dependence of the partial optical path length in the scalp and the weighting factor for the multi-distance probe configuration. The weighting factor ranges from 1.0 to 2.3 and increases with the scalp thickness when the scalp thickness is less than 15 mm.