Partial pathlength

Definition: The path light travels within the fraction of tissue that is of interest, e.g., for functional brain activity, i.e. as opposed to the entire path between the source and detector. For example, the pathlength of the light is different in the scalp layer when compared to the CSF layer. Estimates of partial pathlengths are often obtained from Monte Carlo simulations, which numerically simulate the path taken by individual photons in tissue. It is the path only in the activated region in the inter-optode distance, multiplied by partial pathlength factor (PPF), which is the scaling factor that relates inter-optode distance to the average pathlength light travels within the activated region.

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References:

https://doi.org/10.1364%2FBOE.7.005104

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