Spectral transmittance and contrast in breast diaphanography

Diaphanography is an imaging technique using transillumination with visible and near-infrared radiation, and a video camera, to diagnose breast disease, including cancer. Originally based on luminance contrast only, there is now interest in false-color multispectral imaging in selected spectral bands to improve tissue differentiation. Some success has been achieved, but the scientific basis for the results was unknown. This research is concerned with measurements of the diffuse transmittance of breast tissues as a function of wavelength in the 600-1060 nm range (and calculations of contrast with a one-dimensional diffusion theory model). Carcinoma and glandular tissues were found to have similar spectral transmittances with an increase in transmittance between 750 and 900 nm, and an absorption window around 960 nm. Adipose tissue showed a distinct transmittance minimum at 930 nm. In vivo measurement of an intact normal breast showed a minimum at about 825 nm, as yet unexplained. The transmittance data and reflectance data were used to derive the scattering and absorption coefficients. The diffusion length was also determined from radiance versus depth measurements. These coefficients were used for calculations of contrast in a one-dimensional slab model, with and without a layer of cancerous tissue positioned between two slabs of normal tissue.