Simulating light propagation in brain tissue using ray tracing

The advent of two-photon fluorescence microscopy (TPFM) has opened great opportunities in neurosciences. However, data interpretation of TPFM on dyes with small signal changes such as beta-nicotinamide adenine dinucleotide (NADH) face enormous challenges because the measured signal change is distorted by hemodynamic changes. Prior work by Baraghis et al corrected for this using a single value found empirically. We calculate the point to point correction factor using a 3D microvasculature and check the validity of the single value correction scheme. We use ray tracing scheme to simulate two-photon fluorescence and consider light scattering and absorption due to blood vessels. We calculated the correction factors of NADH signal in a rat model and found that the correction factor was homogeneous beyond 140 microns below the cortical surface, indicating that a single value correction scheme may be adequate in deeper tissues. We will present our new results on a mouse model to test the generality of the single value correction scheme. Our study allows more accurate interpretation of functional imaging studies.