A Time Resolved Spectroscopic (TRS) Study of Migration of Visual to Infrared Waves in Brain Tissue in Relation to Absorption of Hemoproteins

Previous optical spectroscopic studies of brain tissue revealed that only short photon migration distributions yeilds absorption spectra in the visual wavelength range (Heinrich et al. 1985), while longer wavelengths penetrated over greater distances (Brazy et al., 1985). The alpha and beta bands of hemoproteins in brain tissue have extremely high absorption coefficients which reduce the length of light migration distributions. This phenomena can be explained by photon migration theory. As shown in Figure 1A, in scattering media such as a brain tissue, light path lengths have a distribution function. In this figure, the Y-axis represents the log of photon intensity (I) or number of photons, and the X-axis represents time in nanoseconds. Migrating light path lengths (L), can be represented by use of the conversion factor: 1 ns = 23 cm (light path length in water).