Photothermolysis of blood vessels using indocyanine green and pulsed diode laser irradiation in the dorsal skinfold chamber model

BACKGROUND AND OBJECTIVE: For the treatment of vascular lesions, the use of laser light absorbed by the endogenous chromophore hemoglobin may still be improved. MATERIALS AND METHODS: Laser treatment (lambda(em) = 805 nm; fluence rate: 106 kW/cm2; fluence: 3.2 J/cm2 (3 milliseconds)), of blood vessels directly after i.v. application of indocyanine green (ICG) (ICG-concentration: 0, 2, or 4 mg/kg body weight (b.w.)) (n = 14,117) was investigated in the skinfold chamber model. Vessel diameters (1-351 microm) were measured using intravital fluorescence microscopy up to 24 hours following irradiation. Histology was taken 1 or 24 hours after irradiation. Results were compared to a mathematical model based on the finite element method. RESULTS: The reduction of blood vessel perfusion was proportional to ICG-concentration and pulse duration; only a 30 milliseconds pulse duration (2 or 4 mg/kg b.w. ICG-concentration) induced a loss of perfusion even of blood vessels with a diameter <30 microm. Histology revealed photocoagulation of blood vessels up to 24 hours. Results were in agreement with mathematical calculations. CONCLUSION: ICG-mediated laser irradiation induces irreversible photocoagulation of blood vessels of all diameters in this model.