Fig. 3.

Monte Carlo comparisons between the time-resolved reflectance contrast due to a realistic absorption change $\mathrm{\Delta }{\mu }_a$ within a volume of $1000{\mathrm{mm}}^3$ (dotted curves) and that of an equivalent black sphere $V_{\text{black}}$ (solid curves). A semi-infinite medium with ${\mu }_s^{\prime }=1{\mathrm{mm}}^{-1}$ and refractive index equal to 1.33 is considered. Four realistic inhomogeneities with different values of $\mathrm{\Delta }{\mu }_a$ (rows) were positioned at increasing depths $z_i/\mathrm{mm}=10$, 15, 20 (columns) and compared to the equivalent black inclusions. The plots display the relative contrast $|C(t)|$ for three different arrangements of source, detector, and inclusion, namely reflectance measurements at $\rho =5\mathrm{mm}$ (R5) and $\rho =30\mathrm{mm}$ (R30) with the inclusion set midway ($x_i/\mathrm{mm}=2.5$, 15; $y_i=0$) between source [placed at (0,0,0)] and detector. The last case (R30S) refers to $\rho =30\mathrm{mm}$ with an $x$-offset of 15 mm with respect to the midplane, i.e., $x_i=30\mathrm{mm}$, $y_i=0$. The results are independent of ${\mu }_a$.