CONTINUOUS-WAVE LASER ABLATION OF TISSUE - ANALYSIS OF THERMAL AND MECHANICAL EVENTS

Thermal and mechanical events during continuous wave (CW) laser ablati on of biological and phantom media were investigated. Porcine aortae, collagen fibers, and polyacrylamide control samples were subjected to argon laser irradiation while infrared and high-speed (240 images/s) v ideo cameras were used to monitor their surfaces. Subsequent analysis of simultaneous changes in surface temperature and physical features c orrelated thermal and mechanical events. Video images recorded prior t o ablation onset of tissue slabs clearly revealed two distinct phases: 1) progressive growth of a surface dehydration zone, and 2) surface d eformation, implying subsurface bubble formation. Surface temperature recordings and video imaging revealed that the onset of CW ablation of soft biological media often initiated with a violent explosion, surfa ce tearing, and tissue ejection. Histological inspection revealed inte nse coagulation in superficial layers near the irradiation site, where as chiefly mechanical disruption was noted at the base of the crater. Ablation characteristics were consistent with theoretical calculations which indicate subsurface temperature peaks that increase in magnitud e and surface proximity as energy deposition rates are increased. Resu lts also suggested that mechanical properties of target media strongly influenced the extent of pressure built up, the nature of ablation on set, and the characteristics of the overall ablation pathway.