Figure 7.

Comparison between diffusion equation, Monte Carlo method and SP_N approximations in the heterogeneous phantom when g = 0.0 and n_b = 1.37. μ_s and μ_a of the big cylindrical component of the phantom are fixed to 0.5mm⁻¹ and 0.005mm⁻¹ respectively. To the small cylindrical part, the ${\mu }_s^{\prime }/{\mu }_a$ ratios of (a), (b) and (c) are 50.0, 5.0 and 2.0 respectively. MC/SP_i (i = 1, 3, 7) denote the ratios and “SP_j to SP₇” (j = 1, 3) are the relative errors.