The absorption, emission, and convolution steps described above were implemented in a Matlab (from MathWorks, Natick, Massachusetts) routine. All Monte Carlo calculations were done on 7 mm by 6 mm $r-z$ grids with a step-size of 0.02 mm. Test runs showed that photons that penetrate deeper than 6 mm or further than 7 mm from the source fiber have a negligible contribution to the measured fluorescence. The source and collection fiber had a numerical aperture of 0.22 and a core diameter of 200 μm. The look-up tables were calculated on a $28\xd720\xd728\xd720\u2009\u2009\mu sx\u2032\u2212\mu ax\u2212\mu sm\u2032\u2212\mu am$ grid. The grid values were 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 10, and $12\u2009\u2009mm\u22121$ for $\mu sx\u2032$ and $\mu sm\u2032$ and 15, 8, 6, 5, 4, 3, 2.5, 2, 1.5, 1.25, 1, 0.75, 0.5, 0.25, 0.125, 0.1, 0.05, 0.025, 0.01, and $0\u2009\u2009mm\u22121$ for $\mu ax$ and $\mu am$, respectively. This grid covers typical values encountered in tissue (a few $1\u2009\u2009mm\u22121$ for $\mu s\u2032$ and of the order of few $0.1\u2009\u2009mm\u22121$ for $\mu a$). The Monte Carlo simulations were run for 250,000 photon packages both for the excitation and the absorption phase (except for $\mu am=0$, where the number was reduced to 100,000). Calculating the full look-up table took about three weeks on a standard office PC. Information about the validation of the Monte Carlo routine can be found in the ^{1}.