NONCONTACT TISSUE ABLATION BY HOLMIUM - YSGG LASER-PULSES IN BLOOD

To assess the feasibility of intra-arterial tissue ablation by Holmium:YSGG laser pulses (2.1 mu-m) in a noncontact mode, the transmission of the laser pulses through saline and blood was measured. The temporal interaction between the 500 mu-s laser pulse and saline at the fiber tip was investigated with time-resolved flash photography. The penetration depth in blood and saline depended on the fiber output energy. In blood at 37-degrees-C, the penetration depth varied from 1.2 to 2.1 mm for intensities of 3.1 to 12.4 J/mm2 per pulse, respectively, whereas its theoretical value for water is 0.33 mm, which is based on the measured absorption coefficient of 3.0 +/- 0.1/mm. The large penetration depth was due to the development of a transparent vapour cavity around the fiber tip. In saline, its maximum length was 4.7 mm. Its maximum width was 2.8 mm. The lifetime of the cavity was 450 mu-s. In blood, ablation of porcine aorta was feasible at a distance of 3 mm. Large fissures observed in adjacent tissue are likely to be caused by the expansion of the vapour cavity. We conclude that, due to a "Moses effect in the microsecond region," Holmium: YSGG tissue ablation is possible through at least 2.7 mm of blood.