Theoretical investigation of photon mean partial pathlengths in multilayered turbid media

VERA, DEMIÁN A.; GARCÍA, HÉCTOR A; CARBONE, N A; WAKS SERRA, MARÍA V; IRIARTE, DANIELA I; POMARICO, JUAN A

Munich

Conferencia; European Conference on Biomedical Optics (ECBO 2023); 2023

Optical Society of Amereica (OSA)

● Functional Near Infrared Spectroscopy (fNIRS) can be used to non-invasively studybrain haemodynamics1.● Absorption changes in light signals are related to oxy- and deoxyhaemoglobin (HbOand HbR, respectively) changes by means of the mean partial pathlengths (MPPls)of photons through the scalp, skull, cerebrospinal fluid, gray matter, white matter,each of them characterized by an absorption coefficient (μa), a reduced scatteringcoefficient (μs´) and a refractive index (n).● Historically, MPPLs have been computed with the help of Monte Carlo simulations2,which implies long computation times and highly demanding hardware capabilities,preventing real-time measurements.● Most commonly used processing/analysis fNIRS tools make use of homogeneousmodels of the human head to obtain analytical MPPLs3, which are rather inaccuratesince they assume concentration changes take place all over the whole volumeinstead of limited regions such as the gray matter and the scalp.● Different strategies have been implemented to overcome this issue4, but the signalof interest (related to the gray matter) is susceptible of being corrupted by spuriousinfluences from other tissues.● Recently, some of the authors developed a method to analytically compute MPPLsin turbid media of up to four layers in a matter of milliseconds5. This model is a morerepresentative scheme of the problem of light propagation in the human head, and italso allows real-time implementations.● In this work, we extend the previous results to an arbitrary number of layers,increasing in this way the specificity of each layers´ information, allowing to modeltissue types usually packed together (such as the meninges) or even studying thepenetration depth of photons for different source-detector arrays.