Depth-sensitive fluorescence detection of dyes in tissue phantoms

It is well known that tumours can be detected by fluorescence imaging after administration of suitable photosensitisers. The tumour's thickness, however, an important diagnostic parameter, cannot be assessed by optical methods up to now. We show that depth resolution can be achieved in the case of a fluorescent dye distributed homogeneously in a superficial region of a light scattering medium. Diffusion Theory shows that the ratio of the fluorescence measured at different illumination angles is over a wide range sensitive to the thickness of the dye containing layer only, regardless of the dye concentration. For the experimental proof, a new temporally and mechanically stable tissue phantom system was developed. The experimental results on tissue phantoms confirm the predicitons of Diffusion Theory.