Characterization of photoablation versus incidence angle in soft tissue laser surgery: an experimental phantom study

The removal of tissue with a laser scalpel is a complex process that is affected by the laser incidence angle on the surface of the tissue. Current models of laser ablation, however, do not account for the angle of incidence, assuming that it is always normal to the surface. In order to improve ablation modeling in soft tissue, this work characterizes photoablation crater profiles at incidence angles ranging from 0 degrees to 45 degrees off perpendicular. Simulated results, based on a discretized steady-state ablation model, are generated for comparison based on the assumption that material removal occurs in the direction of the laser. Experiments in an agarose-based, homogeneous soft tissue phantom are performed with a carbon dioxide (CO2) laser. Surface profiles of the craters are acquired using a micro x-ray computed tomography scanner (Micro-CT) and compared to results from the simulation. The difference of the simulated and experimental results are measured and the error analysis is reported.