Spectroscopic time-resolved diffuse reflectance and transmittance measurements of the female breast at different interfiber distances

The first, to our knowledge, in-vivo broadband spectroscopic characterization of breast tissue using different interfiber distances as well as transmittance measurements is presented. Absorption and scattering properties were measured on six healthy subjects, using time-resolved diffuse spectroscopy and an inverse-model based on the diffusion equation. Wavelength-tunable picosecond-pulse lasers and time-correlated single-photon counting detection were employed, enabling fully spectroscopic measurements in the range 610 – 1040 nm. Characterization of the absorption and reduced scattering coefficients of breast tissue was made with the aim of investigating individual variations, as well as variations due to different measurement geometries. Diffuse reflectance measurements at different interfiber distances (2, 3 and 4 cm) were performed, as well as a measurement in transmittance mode, meaning that different sampling volumes were involved. The results show a large variation in the absorption and scattering properties depending on the subject, correlating mainly with the water vs. lipid content of the breast. Intra-subject variations, due to different interfiber distance or transmittance mode, correlate with the known structures of the breast, but these variations are small compared to the subject-to-subject variation. The intra-subject variations were larger for the scattering data than the absorption data; this is consistent with different spatial localization of the measurements of these parameters, which is explained by photon migration theory.