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Proceedings Paper

Damage induced by pulsed IR laser radiation at transitions between different tissues
Author(s): Martin Frenz; Charlotte Mischler Greber; Valerio Romano; Martin Forrer; Heinz P. Weber
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Paper Abstract

Due to their strong absorption in water IR-lasers are excellent sources for precision cutting with minimal thermal damage in various fields of medicine. To understand the laser tissue interaction process one has to take into account the liquefaction of target material at the region of radiation impact. The dynamics of the created liquid may cause unexpected and undesirable effects for surgical laser applications. We studied the thermal damage along the walls of incision craters in terms of the elastic material properties and the dynamics of the drilling process. We show that the extension of thermally altered tissue is strongly influenced by the amount of hot liquefied tissue material remaining in the crater. When drilling into mechanically homogeneous materials this amount is essentially determined by the laser intensity used. However, when drilling through a composite structure consisting of various tissue types with different material properties, this is no longer the case. Even at low intensities, the damage zone varies substantially between the different layers. In our investigations we compared histologically and ultrastructurally the instantaneously created damage in the connective tissue and the subjacent skeletal muscle of skin after laser cutting, with long-time heating injuries. This comparison allows a differentiation between thermal and mechanical damage and an estimation of the minimum temperature created in the crater during the laser impact. The light microscopical examinations shows that the thermal damage in the connective tissue is about three times smaller than in the subjacent muscle layer. Comparative studies made with a composite structure consisting of the tissue substitutes gelatin and agar reveal that the unexpectedly large damage in the skeletal muscle layer is a result of the abrupt change of the elastic properties at the material transition. This discontinuity changes the ejection dynamics leading to a confinement of hot liquefied tissue material. The trapped hot liquid acts as an efficient heat source observed in the large damage of the muscle layer.

Paper Details

Date Published: 1 June 1991
PDF: 7 pages
Proc. SPIE 1427, Laser-Tissue Interaction II, (1 June 1991); doi: 10.1117/12.44084
Show Author Affiliations
Martin Frenz, Univ. of Berne (Switzerland)
Charlotte Mischler Greber, Univ. of Berne (Switzerland)
Valerio Romano, Univ. of Berne (Switzerland)
Martin Forrer, Univ. of Berne (Switzerland)
Heinz P. Weber, Univ. of Berne (Switzerland)

Published in SPIE Proceedings Vol. 1427:
Laser-Tissue Interaction II
Steven L. Jacques, Editor(s)

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