Noninvasive determination of absorption and reduced scattering coefficients of adult heads by time-resolved reflectance measurements for functional near infra-red spectroscopy

Absorption and reduced scattering coefficients (μ_a and μ´_s) of adult heads have been noninvasively determined by time-resolved reflectance measurements. The finite difference time domain (FDTD) analysis was used to calculate time-resolved reflectance from realistic adult head models with brain grooves containing a non-scattering layer. In vivo time-resolved reflectances of human heads were measured by a system composed of a time-correlated single photon counter and a diode laser. By minimizing the objective functions that compare theoretical and experimental time resolved reflectances, μ_a and μ´_s of brain were determined. It became clear that time-resolved measurements have enough sensitivity to determine both μ_a and μ´_s for superficial tissues, gray matter and white matter, except μ_s for white matter.