Narrow-band imaging (NBI) or «optical narrowband filter» is a novel system of endoscopic visualization in real time which significantly improves visualization of the vascularity and the tissue surface, allowing better characterization of abnormal findings. Applies a technology based on narrowing of the white light spectrum commonly used endoscopically through a system of filters. Thus, this system allows two wavelengths (415nm blue light and 540nm green light) to reach the surface of the tissue and reflected back on a chip that captures the image. Both wavelengths correspond to peaks in the absorption spectrum of the oxidized hemoglobin light, fact that allows to appreciate more clearly the vascular network in tissue surface. Blue light penetrates tissues poorly (0’17mm) and as a result allows to see the superficial vascular networks, while green light penetrates deeper and shows sub-epithelial vessels. When both are combined you can observe an image of the tissue surface with high contrast.