A three-zone model of soft-tissue damage by a CO2 laser

Area of Science:

• Biomedical Engineering
• Laser-Tissue Interactions
• Soft Tissue Physics

Background:

• Carbon dioxide (CO2) lasers are used in surgery, causing distinct thermal damage zones in soft tissues.
• Understanding these damage zones is crucial for optimizing laser procedures and minimizing collateral injury.

Purpose of the Study:

• To develop a predictive model for the depths of CO2 laser-induced damage zones in soft tissue.
• To investigate the influence of laser parameters and tissue properties on damage zone dimensions.

Main Methods:

• A theoretical model was developed to predict the maximum depths of carbonized, vacuolated, and coagulated zones.
• The model considers heat transfer, phase transitions (water to steam), and laser absorption properties of the tissue.
• The effects of incident irradiance, tissue absorption coefficient, and pulsed laser radiation were analyzed.

Main Results:

• The model predicts distinct damage zones: carbonized, vacuolated (steam formation), and coagulated (<100°C).
• Vacuolated zone thickness depends on tissue absorption coefficient, independent of incident irradiance.
• Carbonized and sub-boiling coagulated zone depths decrease with increasing irradiance, with coagulation depth also influenced by laser penetration.

Conclusions:

• The proposed model provides a framework for predicting CO2 laser thermal damage in soft tissues.
• Irradiance significantly impacts carbonized and coagulated zone depths, while tissue optical properties are key for vacuolated zone formation.
• Experimental validation of the model's predictions is recommended.