a method and an apparatus for the in vivo , non - invasive , early detection of alterations and mapping of the grade of these alterations , causing in the biochemical and / or in the functional characteristics of the epithelial tissues during the development of tissue atypias , dysplasias , neoplasias and cancers is presented . the method is based , at least in part , on the simultaneous measurement of the spatial , temporal and spectral alterations in the characteristics of the light that is re - emitted from the tissue under examination , as a result of a combined tissue excitation with light and special chemical agents . the topical or systematic administration of these agents result in an evanescent contrast enhancement between normal and abnormal areas of tissue . the apparatus enables the capturing of temporally successive imaging in one or more spectral bands simultaneously .