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 skin flap model using a specific indocyanine green (ICG) formulation. STUDY DESIGN/
MATERIALS AND METHODS: Experiments were performed in a hamster skin flap model after injection of ICG in aqueous solution (ICGA), or after injection of a specific formulation of ICG (ICG in emulsion: ICGE). Laser irradiation was achieved 30 minutes after injection with a 300 microns fiber connected to a 805 nm diode laser (power = 0.8W, spot 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 concentration of ICG in blood is higher (2.27 +/- 0.4, P < 0.003) for ICGE compared to ICGA. With ICGA, vessel coagulation required a minimum fluence of 240 J/cm2, which led to very significant skin damage. Conversely with ICGE, vessel coagulation required a fluence of 120 J/cm2. 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 blood vessels after a few minutes, are alleviated when ICG is used in emulsion. ICG in emulsion increases the circulating half-life of ICG and moreover confines ICG in the vascular compartment. Thanks to this specific property, it is possible to obtain a selective vascular damage 30 minutes after injection.