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Proceedings Paper

Onset of continuous wave Nd:YAG and argon laser tissue ablation
Author(s): Rudolf M. Verdaasdonck; Cornelius Borst M.D.; Martin J. C. van Gemert
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Paper Abstract

To study the onset of tissue ablation by cw laser irradiation, aortic and myocardial bovine tissue samples were exposed in air to a 1 mm diameter laser beam of either 15 W Nd-YAG or 3.5 W Argon. Exposure times varied from 0.1 to 30 s. The surface of the tissue was filmed with a resolution ofO.O1 mm and recorded on video with time coding. A photodiode positioned underneath the tissue samples measured forward transmitted light. After exposure the tissue was processed for histology. The observed phenomena were divided in three phases: Phase A: The tissue surface slightly discolored while the transmission signal remained constant or slightly diminished. Phase B: Simultaneous with a 'pop' sound, the surface rose and the transmission dropped abruptly to about 50 % and remained at this level for several seconds during vaporization of tissue water. Histology showed ruptured layers and multiple vacuoles beneath the surface. Phase C: In the middle of the beam a spot ofcarbonized tissue was formed which grew concentrically from the center while a crater was formed. No drop in the transmission was observed when carbonization started. On the crater bottom carbonization and vaporization followed in rapid succession while light transmission increased. Histology showed along the crater edge a 20 jim thick layer of carbonization and a 200 pm thick layer of vacuoles due to tissue water boiling whereas on the crater bottom these layers were only 10 and 20 jim thick respectively. Thus, the small zone of vacuoles at the crater bottom suggest that a large temperature gradient existed at the ablation front. The 'popcorn' phenomenon is attributed to the explosive formation ofvapor bubbles underneath the tissue surface caused by the anatomically or heat-induced layered structure of the tissue resulting in enhanced reflection and scattering of the laser light due to multiple tissue-vapor transitions.

Paper Details

Date Published: 1 June 1990
PDF: 8 pages
Proc. SPIE 1202, Laser-Tissue Interaction, (1 June 1990); doi: 10.1117/12.17624
Show Author Affiliations
Rudolf M. Verdaasdonck, Univ. Hospital Utrecht (Netherlands)
Cornelius Borst M.D., Univ. Hospital Utrecht (Netherlands)
Martin J. C. van Gemert, Academic Medical Ctr. (Netherlands)

Published in SPIE Proceedings Vol. 1202:
Laser-Tissue Interaction
Steven L. Jacques, Editor(s)

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