When analyzing the data in our concurrent NIRS-fMRI study, we are particularly interested in how the NIRS signals were correlated to the fMRI signal. To answer the question we need to create an ROI (region of interest) in brain which is directly underneath the NIRS channel (which is on the skull). So a projection of the NIRS channel on the brain surface is necessary.
It might be easy if the brain were a perfect sphere, or at least doable if it is smooth. But brain surface is anything but smooth. What we did is:
- Create a brain surface mask. This is easy using BET (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/BET)
- Loop over all voxels on the surface, calculate the distance between the NIRS channel (point A) and the voxel
- Find the voxel which is closest to the NIRS channel (It is point B in the figure below)
