Self-adaptive method to uncouple cortex-related brain activation from superficial effects

We present a method to separate superficial from deeper changes in absorption properties for a time-resolved reflectance measurement on a heterogeneous diffusive medium. The method relies on the derivation of the pathlengths spent by photons in each region as a function of the collection time t. The pathlengths in the superficial layer were assumed to be constant for every t. Conversely, the lower layer pathlengths were derived directly from the time-resolved contrast obtained in correspondence to an expected change in the deeper region properties. The method was applied to the monitoring of an in vivo exercise of finger tapping on a volunteer, permitting to observe quite distinct features for the oxy- and deoxy-hemoglobin changes in the upper and lower regions. ©2008 Optical Society of America.