In order not to rely on other imaging modalities and possible phase function uncertainties, we follow a slightly different approach by measuring the optical properties of a very homogeneous and intensely scattering epoxy phantom (). The only assumptions we make on this phantom are the spatial homogeneity of its optical properties along with its predetermined refractive index values.23 We then determine the phantom’s optical properties (i.e., , , and ) at every imaging point using the product of light source intensity and detection sensitivity as an additional multiplicative fit variable . In a next evaluation step, the derived optical properties are averaged and assumed constant for all imaging points, which leaves the factor as a single and robust fit variable in a second reevaluation of the phantom. This fit variable quantifies the ratio between and the actual reflectance value as predicted by the theoretical model. Display Formula
(3)All subsequent measurements are multiplied by the obtained map , serving as an intensity reference that quantifies both the light source intensity and the detection efficiency at the same time. Note that is independent of spatial frequency.