Inverse adding-doubling (IAD) is used to calculate the wavelength-dependent optical properties (e.g., absorption and reduced scattering coefficients) from all the thin samples.19 The IAD method calculates optical properties (i.e., absorption and scattering coefficients) based on measurements of total reflectance and transmittance via an integrating sphere. Additional physical properties, such as the sample thickness, index of refraction of the medium, , and scattering anisotropy factor, , are also required in order to use the IAD approach to calculate the absorption and scattering coefficients. For this investigation, we have assumed an index of refraction for PDMS to be 1.43, based on previous literature.3,5 We also assumed that the anisotropy factor was between 0.8 and 0.9. However by preparing samples that are 1 mm thick, and given the anticipated reduced scattering values of these phantoms, we anticipate that scattered light in both reflectance and transmittance geometries will be primarily isotropic, thereby minimizing any influence from anisotropic scattering signals. This will also be verified in the results section.