Principally the laser-tissue interaction is due to the absorption of photons and the duration of laser application. Thus, the absorbed (deposited) photon energy is converted to another form of energy in the tissues (for e.g., thermal, chemical and mechanical energy). The depth of tissue penetration by the laser is determined or dependent on different wave lengths of the laser. The main thermal changes caused are coagulation and vaporisation of the tissues. The photothermal changes are mostly brought about by the use of Nd:YAG and Argon Laser. Photoablation and photodisruption (optical penetration) are grouped into photoionising and oligothermal changes which is characterized by application of high density rays for a very short affection time (laser pulse in nsec likewise in µsec). The photoablative change is achieved by the pulsed Excimer-Laser. The photoablation leads to rapid necrosis of the target tissue with minimal thermal effect of the surrounding tissues. Hence, the necrosed zone of the surrounding tissue is less than 50 µm whereas the thermal necrosis of the target zone is more than 50 µm.

 

Document Date: 2005/09/07   Author: unknown

|  Zurück zum Seitenanfang | Zur Navigationshilfe