18 Bronchology – Past, Present and Future Diagnostic Procedures Light can be described as a wave with a characteristic wavelength or as a par- ticle with a characteristic energy, called photon. Photons can be involved when an electron or an atom changes its state of energy. The energy is released in dis- crete portions or “quanta”. Hence, the energy spectrum of atoms is discrete. In lasers, electrons are pumped from the ground state to an excited state. With the help of two mirrors, one reflecting 100% of the light at the desired wavelength and the other partially reflecting the light, a coherent and monochromatic (single wavelength) laser beam is produced. When tissues are illuminated by light one of four things can happen: (1) the light can be reflected from the surface, or (2) transmitted through the tissue, (3) scattered in or (4) absorbed by the tissue. The effect of the laser beam depends on its wavelength, intensity, duration of exposure, and tissue-specific response. Krypton–ion (Kr⁺, 405 nm, visible blue) and He-Cd (442 nm, visible blue) lasers are used to elicit fluorescence, whereas carbon dioxide (CO2, 10.600 nm) is suitable for cutting, Neodymium Yttrium- Aluminum Granate (Nd-YAG, 1.060 nm) for deep heating and Argon-ion (Ar, 488 nm and 514 nm, visible blue green) for heating and fluorescence. Fluorescence is the optical property of certain compounds (fluorochromes) of emitting light while exposed to light, the wavelength of the emitted light being only slightly longer than that of the light absorbed. The tissue-inherent compounds capable of fluorescence are called fluorochro- mes. Organs contain different concentrations of these fluorochromes giving rise to an “organ-specific” pattern. Known fluorochromes include elastin, collagen, porphyrin, tryptophan and various derivatives, and flavines, which play a role in the oxidative NAD/NADH metabolism. Fig. 15 Heme biosynthesis with 5-aminolevulinic acid as the starting product. Glycine + Succinyl CoA (Feedback  control) 5-Aminolevulinic acid synthetase 5-Aminolevulinic acid 5-Aminolevulinic acid dehydrase Porphobilinogen deaminase Porphobilinogen Uroporphyrinogen I Uroporphyrinogen III Coproporphyrinogen III Coproporphyrinogen I Coproporphyrin I Uroporphyrin III Coproporphyrin III Protoporphyrinogen IX Protoporphyrin IX Ferrochelatase + Fe ²⁺ Heme Protoporphyrinogen oxidase Coproparphyrinogen oxidase Porphobilinogen deaminase + Uroporphyrinogen III cosynthase Uroporphyrin I Basic Principles of the Biophysics of Autofluorescence/ Fluorescence Back –––––––Table of Contents–––––––Next Back –––––––Table of Contents–––––––Next