Near Infrared (NIR) extinction measurements can be used to determine the cerebral hemodynamics of adult patients. To be able to interpret and verify measurement data, it is necessary to know the three-dimensional light intensity distribution in the human head. This light intensity map can advantageously be created by numerical simulations. Such simulations of light intensity in the head are complex, since the light is crossing several tissue types with very distinct optical properties. The Monte-Carlo method proved to represent a reliable tool for simulation of light intensity in turbid media. The desired result of a Monte-Carlo simulation is the spatially resolved average light intensity, which has to be derived from the statistical output of the Monte-Carlo simulation.
We propose a novel analysis method which directly tracks the intensity based on a line-drawing algorithm to attain a 3D intensity map of the whole computational domain. The proposed method largely operates independently of the underlying Monte-Carlo algorithm itself. The algorithm is verified through comparison with analytical approximations of the Radiative Transport Equation. As a challenging example, the simulation of the light intensity distribution inside the human head based on segmented MRI data is presented.