Bronchology – Past, Present and Future Diagnostic Procedures 21 2.  Indirect Imaging Fluorescence Endoscopic System using HeCd-Laser Beam This is a non-invasive light-induced fluorescence system based on the observa- tion that malignant tissue can be distinguished from normal tissue by a notice- able reduction in its autofluorescence. When a monochromic light beam of 442 nm is directed at the mucosa, sub- epithelial fluorochromes are stimulated to emit light of a longer wavelength 500 nm broadband (green). In in-situ carcinoma or dysplasia, the intensity of the emitted light is estimated to be ten times lower. Usually, this effect is more pro- nounced  in  in-situ  carcinomas.  The  reduction  in  fluorescence  is  related  to epithelial thickening and tumor hyperemia in which hemoglobin absorbs most of the blue and green light. Other factors include reduced number of fluoro- chromes in the tumor and redox changes in the tumor matrix. Using false-color technology, a computer monitor provides a real-time video image of the bronchial mucosa. The system uses a HeCd-Laser as the light source, which generates a 442 nm monochromatic beam. The light is guided to the mucosa via a conventional fiberscope. The red and green emissions are detected and recorded by two CCD cameras and the digitized impulses are transmitted to an imaging board and monitored. Normal mucosa is light green, whereas dysplasia and in-situ carcinoma  appear  reddish-brown.  The  procedure  is  performed  under  local anesthesia and allows biopsies to be taken. Fig. 18 Schematic Drawing of the Indirect Imaging Fluorescence Endoscopic System using HeCd-Laser beam. Fig. 17 Diagramm of tissue autofluorescence. Normal Dysplastic Mucosa Sub- mucosa red (630 nm) blue (442 nm) green (520 nm) red (630 nm) Image processing Monitor Data input System control Image aquisitition CCD-Cameras Laser light Image board Back –––––––Table of Contents–––––––Next Back –––––––Table of Contents–––––––Next