A basal cell carcinoma (BCC) skin tissue model was used to evaluate the effectiveness of the hybrid method. The BCC usually originates from the basal layer of the epidermis and frequently grows downward deeply into the dermis,8 thus it is induced into the dermis in our theoretical tissue model as shown by the cross-sectional view in Fig. 2. The thickness of the epidermis was set at 80 µm and the thickness of the dermis was set at 4 cm to mimic a thick skin tissue. The epidermal thickness is representative of that on the neck and back.9 The length, width, and thickness of the BCC tumor were all set at 400 µm. The optical properties of the epidermis and dermis were selected from the literature10 and listed in Table 1. A refractive index of 1.4 and an anisotropy factor of 0.8 were used in the entire tissue model including the BCC tumor. The absorption and scattering coefficients of the tumor were varied sequentially to investigate the valid range of the hybrid method. The fiber configuration in Fig. 2 shows the source and detector fibers placed side by side, with both perpendicular to the tissue surface. The bisecting line between the two fibers overlaps with the middle line of the tumor in the width dimension, that is, the dimension in Fig. 2. The two fibers both had a core diameter of 200 µm and NA value of 0.22. The refractive indices of the fibers were set at 1.47. In total, two sets of tests were performed. In the first set, the absorption coefficient, , of the tumor was varied from 1% to 400% of that of the dermis, while the scattering coefficient, , of the tumor was kept identical to that of the dermis. In the second set, the scattering coefficient, , of the tumor was varied from 25% to 190% of that of the dermis, while the absorption coefficient, , of the tumor was kept identical to that of the dermis. Diffuse reflectance values, which refer to the ratio between detected and incident powers in this paper, calculated by the hybrid method were compared to those from independent MC simulations (no scaling or perturbation methods were used), which were run by using a previously validated MC code,11 to evaluate the effectiveness of the hybrid method.