FIG. 1.

A sphere with 4-layer tissues (scalp, skull, CSF, and brain) to mimic an adult human head model. One source (S) and three detector (D1–D3) fibers were placed on the forehead of the model (a). S-D separations were set as 2.0, 2.5, and 3.0 cm, respectively. The scalp, skull, and CSF with the thicknesses of 0.4, 0.6, and 0.1 cm, respectively were illustrated in the cross-section view of the sphere model (b). Tissue optical properties (μ_a, μ_s', and αD_B) of the 4-layer tissues were assigned according to the literature.¹¹