The efficiency of laser ablation of thrombus depends on spot size, pulse energy and repetition rate. A 1\mms pulsed dye laser (504nm) was used to ablate a gelatin-based thrombus model containing an absorbing dye under water. The gelatin was confined in 3mm inner diameter tubes and pulse energies of 25-100mJ were delivered via 300, 600, and 1000µm core diameter fibers. The experiments were conducted at pulse repetition rates of 3Hz and 10Hz. The amount of gelatin removed was measured using a spectrophotometric method and ablation efficiency was defined as mass removed per pulse per unit energy. Flash photography was used to visualize the ablation process in 1cm cuvettes. Results: More material was removed using bigger fibers in the 3mm tubes at similar pulse energies. The amount of gelatin removed per pulse increased linearly with pulse energy. There was no significant change in the amount removed at pulse repetition rates of 3Hz and 10Hz. In the 1cm cuvettes, the ablation mass was roughly the same with both the 300µm and 1000µm fibers. Flash photography of the ablation process in 1cm cuvettes showed that less than 1% of the laser energy went into formation of a vapor bubble. The mass removed increased roughly linearly with bubble energy. Conclusions: Ablation mass increases linearly with pulse energy, but does not have a direct relationship with radiant exposure. It is independent of the repetition rate under 10Hz.
U. S. Sathyam, A. Shearin, and S. A. Prahl. The effect of spotsize, pulse energy, and repetition rate on microsecond ablation of gelatin under water. In S. L. Jacques, editor, SPIE Proceedings of Laser-Tissue Interaction VI, volume 2391, pages 336-344, 1995.