Background and Objective: Simultaneous irradiation and viewing of 10-120 m cutaneous blood vessels were performed to investigate the effects of 2-s 577-nm dye laser pulses. Study Design/Materials and Methods: A modified scanning laser confocal microscope recorded vessel response to different radiant exposures (J/cm 2 ). Probit analysis determined the 50% probability (''threshold'') radiant exposure necessary to cause embolized or partly occluding coagula, coagula causing complete blood flow stoppage, and hemorrhage. Results: A statistically significant difference in the threshold radiant exposure existed for each damage category for blood vessels 10-30 m in diameter, but not for larger vessels. For vessels over 60 m, complete flow stoppage was unattainable; increasing laser pulse energy produced hemorrhage. In larger vessels, coagula often were attached to the superficial vessel wall while blood flowed underneath. Monte Carlo optical and finite difference thermal modeling confirmed experimental results.
Conclusion:
These results provide insight into the role of pulse duration and vessel diameter in the outcome of pulsed dye laser irradiation. Lasers Surg. Med. 24:236-243, 1999.