optical tracking of diffusion; brain extracellular space; diffusion equation; Fourier transform; point spread function
An improved version of the Integrative Optical Imaging (IOI) method for diffusion measurements in a geometrically complex environment of the brain extracellular space has been developed. We present a theory for this Fast Optical Tracking Of Diffusion (FOTOD) which incorporates a time-dependent effective diffusion coefficient in homogeneous anisotropic media with time-dependent nonspecific linear clearance. FOTOD can be used to measure rapid changes in extracellular diffusion permeability that occur, e.g., during brain insults. The achievable time resolution is approximately one second, a ten fold improvement compared to the traditional IOI method.