Reconstruction of light absorption changes in the human head using analytically computed photon partial pathlengths in layered media

Abstract

Functional Near Infrared Spectroscopy has been used in the last decades to sense and quantifychanges in hemoglobin concentrations in the human brain. This non invasive technique can deliveruseful information concerning brain cortex activation associated with different motor/cognitivetasks or external stimuli. This is usually accomplished by considering the human head as ahomogeneous medium; however, this approach does not explicitly takes into account the detailedlayered structure of the head and thus, extracerebral signals can mask those arising at the cortexlevel. This work improves this situation by considering layered models of the human headduring the reconstruction of the absorption changes in layered media. To this end, analyticallycalculated mean partial pathlengths of photons are used, which guarantees fast and simpleimplementation in real-time applications. Results obtained from synthetic data generated byMonte Carlo simulations in two- and four-layered turbid media suggest that a layered descriptionof the human head greatly outperforms the typical homogeneous reconstructions, with errors,in the first case, bounded up to ∼ 20% maximum, while in the second case the error is usuallylarger than 75%. Experimental measurements on dynamic phantoms support this conclusion.