The propagation distance between interactions, , given by Eq. (1), is also affected by the difference in interaction cross-sections. In Eq. (1), the interaction coefficient, , corresponds to the overall interaction cross-section of a material. A larger corresponds to a larger interaction cross-section, and, in turn, a larger interaction volume. Similar to how Schmitt and Kumar rescaled the total scattering coefficient for the total scattering cross-section,18 and how Verkruysse et al. rescaled the absorption and scattering coefficients,17 we redefined as a weighted average of the interaction strengths of the two materials. Thus, the new , , has the form Display Formula
(9)and is used in place of in Eq. (1).