Local scattering anisotropy of the skin as a possible factor of fluorescence borders distortion of neoplasms

The use of protoporphyrin IX fluorescence imaging in skin tumors is limited by the complexity of light propagation in tissues. A non-invasive scat- tering anisotropy test (comparison of the fluorescence pattern of a tumor with that of a point source applied to the same spot) would be useful in distinguishing between cases of subsurface tumor growth and local fluorescence pattern distortions. However, the knowledge is missing of whether the distribution from an external light source would be representative. The experiment described here addressed the correlation between patterns in which light is dispersed from an external and an internal source within the same area of the skin. A pig’s head was chosen as the model. Four zones of interest were identified, all different in optical properties. The wavelength of the light source was selected as to simulate the PpIX fluorescence. The correspondence of light distribution patterns was quantified using the correlation method. The results have clearly demon- strated the strong relationship between the fluorescence distribution pattern of a tumor and the condition/topography of the surrounding tissues and proved the possibility of using an external light source to assess the local scattering anisotropy of the skin in vivo.