Bronchology – Past, Present and Future Diagnostic Procedures 19 Fluorescence depends on the source and wavelength, degree of absorption and re-emission of light. At present there are four fluorescence systems used in bronchology for stimulation of subepithelial fluorochromes. 1.  Photofluorescence, (Hayata-Kato) using a krypton-ion laser beam, hematoporphyrin (HPD), and Photodynamic Therapy (PDT). 2.  Indirect Imaging Fluorescence Endoscope using HeCd-Laser Beam 3.  Autofluorescence System (KARL STORZ D-LIGHT AF) using a special Xenon light source, for white light and blue excitation light (380 – 460 nm). 4.  Fluorescence System (KARL STORZ D-LIGHT AF) using 5-Aminolevulinic acid as the active ingredient of the inhalation solution (5-ALA-induced fluorescence diagnostics), blue excitation light (380 – 440 nm). The KARL STORZ D-LIGHT AF System combines methods 3 and 4 in the same instrument. In 1903, von Tappeiner and Jesionek used topical eosin and sunlight to treat skin tumors in the first application of photosensitization. It was discovered that many dyes were taken up preferentially by tumor cells. However, the search for a perfect photosensitizer which should be non-toxic, taken up by malignant cells only, and excited by light of a specific wavelength, is ongoing. In 1974, Thompson showed that Ar-Laser-excited acridine orange possesses the required properties. Many other dyes have since been used for diagnosis and treatment of cancer, i.e. fluoresceine (Moore, 1953), tetracyclines (Rall, 1957) and porphyrins and metallo-porphyrins (Figge, 1948). Hematoporphyrin shows low toxicity and therefore can be administered systemically; it is taken up selectively and retained in malignant tissue. In 1975, Dougherty claimed that HPD can be excited by photons in the pre- sence of oxygen to attain high local cytotoxicity. The study of HPD is continuing at various centers, mainly led by Dorion, Kinsey and Svaasand. Back –––––––Table of Contents–––––––Next Back –––––––Table of Contents–––––––Next