A thermal appraisal of the ablation process in canine aorta in vivo using a 100 μm pulsed Nd-YAG laser

A model has been developed to calculate distal tissue necrosis in vascular tissue after application of a 100μ laser pulse from a Nd-YAG laser (5 kW peak pulse power on a 0.13 mm2 spot size). The model assumes that the temperature profile in the tissue is proportional to the laser light fluence rate and that the distal tissue necrosis depth is that depth in the tissue where there is a temperature increase of 42 °C minus the etch rate (ablation depth per laser pulse). The fluence rate has been calculated using the diffusion approximation to the radiative transport equation. The tissue optical parameters (absorption and reduced scattering coefficients) have been derived from published data. The etch rate used (10μm per pulse) is derived from in vivo experimental results. The model predicts a damage depth varying between 0 and 2.33 mm (mean 1.10 mm) and this is compared with an experimental result (0.77 mm) in dog aorta.