SELECTIVE LASER PHOTOCOAGULATION OF BLOOD-VESSELS IN A HAMSTER SKIN FLAP MODEL USING A SPECIFIC ICG FORMULATION

Background and Objective: The present study was undertaken to evaluate the selective laser photocoagulation of blood vessels in a hamster sk in flap model using a specific indocyanine green (ICG;) formulation. S tudy Design/Materials and Methods: Experiments were performed in a ham ster skin flap model after injection of ICG in aqueous solution (ICGA) , or after injection of a specific formulation of ICG (ICG; in emulsio n: ICGE). Laser irradiation was achieved 30 minutes after injection wi th a 300 mu m fiber connected to a 805 nm diode laser (power = 0.8W, s pot diameter = 1.3 mm and pulse exposure time lasting from 1 to 5 s). Macroscopic observation and acute histology were performed to compare the tissue effects obtained for each ICG formulation and to assess the selectivity of vessel damage. Results: The ICGE clearance process was slowed down as compared to the ICGA process. After 30 minutes, the co ncentration of ICG in blood is higher (2.27 +/- 0.4, P < 0.003) for IC GE compared to ICGA. With ICGA, vessel coagulation required a minimum fluence of 240 J/cm(2), which led to very significant skin damage. Con versely with ICGE, vessel coagulation required a fluence of 120 J/cm(2 ). With such a fluence, no laser effect could be detected on the skin. Histological examination confirmed blood vessels coagulation in depth , whereas epidermis and dermis remained intact. Conclusion: The major restrictions of ICG in aqueous solution, which are the very-short half -life of ICG in blood and consequently the lack of selectivity in bloo d vessels after a few minutes, are alleviated when ICC; is used in emu lsion. ICG in emulsion increases the circulating half-life of ICG and moreover confines ICG in the vascular compartment. Thanks to this spec ific property, it is possible to obtain a selective vascular damage 30 minutes after injection. (C) 1997 Wiley-Liss, Inc.