The blood was assumed to have a hematocrit of 43%, a hemoglobin concentration of $145\u2009\u2009g/l$ blood, and a mean cell hemoglobin concentration of $345\u2009\u2009g/l$ RBC. The wavelength-dependent absorption coefficients for oxygenated and deoxygenated blood ($\mu a,oxy$ and $\mu a,deoxy$) were derived from Ziljstra et al.^{23} A scattering coefficient of blood of $222\u2009\u2009mm\u22121$ at the laser wavelength (780 nm) was used, and at the same wavelength, a Gegenbauer kernel phase function with parameters $gGk=0.948$ and $\alpha Gk=1.0$, resulting in an anisotropy factor of 0.991, was used.^{21} The oxygen saturation ($s$) was given by one parameter and was assumed to be equal in the two dermal layers. The absorption coefficient of blood in layer $n$ was calculated as Display Formula
$\mu a,blood,n(\lambda )=[s\mu a,oxy(\lambda )+(1\u2212s)\mu a,deoxy(\lambda )]cvp,n,$(4)
where $cvp,n$ is a factor compensating for the so called vessel-packaging effect. This factor is given by^{7}^{,}^{8}^{,}^{24}Display Formula$cvp,n(\lambda )=1\u2212exp[\u2212Dn\mu a,blood(\lambda )]Dn\mu a,blood(\lambda ),$(5)
where $Dn$ is the average vessel diameter in layer $n$ (variable parameter twice as high for the deeper dermis layer). It can be realized that $cvp,n(\lambda )\u21921$ when $Dn\u21920$ or $\mu a,blood(\lambda )\u21920$. The absorption coefficient of the two dermal layers was given by ($n\u2208[1,2]$) Display Formula$\mu a,n(\lambda )=fblood,n\mu a,blood,n(\lambda ),$(6)
where $fblood,n$ was the volume fraction in the two dermis layers given by two parameters.