Mieke Bus

39 3 WL SPIES Spectra A SPIES spectra B Light source detector scope Figure 4: Storz Professional Image Enhancement System (SPIES) filters acquired white light images digitally in order to produce enhanced contrast images. Several modes can be used in order to increase viewing comfort for the endoscopist, enhancing sharpness of the displayed images and providing specific colour renderings. Spectral separation within the camera is amplified by adapted colour processing algorithms of the whole spectral light information. Inserts demonstrating upper urinary tumour seen with white light and SPIES Spectra A and Spectra B. Techniques based on fluorescence Photodynamic Diagnosis Photodynamic diagnosis (PDD) employs fluorescence as a contrast mechanism to localize abnormal tissue (table 1). PDD is based on the selective accumulation of a fluorochrome in malignant tissue. Absorption of high-energy light of the appropriate wavelength (i.e. ~400 nm) excites the electro-vibrational state of the fluorochrome. When the molecule relaxes to the ground state a photon is emitted (i.e. 590-700 nm) to account for the energy difference. The fluorescent photon has less energy than the excitation photon; since the energy of light is inversely proportional to its wavelength, the emitted light has a longer wavelength than the illuminating light. Therefore, discrimination between the two types of light is possible (Figure 5). Several exogenous fluorochrome agents have been investigated to induce exogenous fluorescence. Most research in the upper urinary tract has been con- ducted using the approved porphyrin-related fluorochrome 5-Aminolaevulinic acid (5-ALA). Endoscopes with special light sources and filters are used to illuminate tissue with blue light (380-470 nm) that corrects for heterogeneous illumination and distance variations. It also