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 (mu(a) and mu'(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, mu(a) and mu'(s) of brain were determined. It became clear that time-resolved measurements have enough sensitivity to determine both mu(a) and mu'(s) for superficial tissues, gray matter and white matter, except mu'(s) for white matter.