Fig. 4.

Standard deviation of the measured photon counts, $[\mathrm{Var}(M){]}^{1/2}$, as a function of their averages, $E(M)$. Each symbol corresponds to the pair of $E(M)$ and $[\mathrm{Var}(M){]}^{1/2}$ of the measured data from three to four successive photon count data for the various $z_T$ of the milk-only (green circles) or ICG–milk (red squares) targets. The black solid curve indicates $[\mathrm{Var}(M){]}^{1/2}$ obtained by fitting Eq. (15) to the whole data.