RELEASE OF FLUORESCEIN FROM THERMOSENSITI VE LIPOSOMES FOR A QUANTIFICATION OF LASER-INDUCED PHOTOCOAGULATION - IN-VIVO STUDY ON A VASCULARMODEL

Purpose To evaluate the feasibility of thermal damage assessment of bl ood vessels by using laser-induced release of liposome-encapsulated dy e. Methods A skin flap window model of aluminium was implanted on the loose skin on the back of adults Golden hamsters to expose skin blood vessels in vivo. Thermosensitive liposomes (DSPC) Loaded with 5,6-Carb oxyfluorescein were injected together with a specific Indocyanine gree n (ICG) formulation (O/W emulsion) in order to enhance diode laser abs orption. Photocoagulations were then performed on the vessels with a d iode laser (lambda = 810 nm, P = 0.8W, empty set = 1.3 mm, 1 to 6s). F luorescence measurements were realized with an ultra high sensitivity intensified camera (Hamamatsu Argus 50 imaging system). Results Two di fferent fluorescence intensity curves corresponding to the variability of absorption of the targets were observed. Variability was related t o the amount of ICG. For each curve, 3 zones were identified : (i) for fluences ranging from 60 +/- 20 J/cm(2) to 110 +/- 20 J/cm(2) a trans ient intravascular fluorescence was observed only for the laser pulses targeted on the vessels, (ii) for fluences ranging from 110 +/- 20 J/ cm(2) to 190 +/- 20 J/cm(2) a permanent fluorescent spot limited to th e vessel was observed for the laser pulses targeted on the vessels; fo r the laser pulses targeted on the skin a transient low fluorescence c ircular spot was observed. For this fluence range a selective photocoa gulation of a vessel was performed. (iii) for fluences ranging from 19 0 +/- 20 J/cm(2) to 300 +/- 20 J/cm(2) persistent intense fluorescence spots were observed on both skin and vessels. This type of fluorescen ce was related to art overdosage. Conclusion These results are in fair agreement with the data of the literature about liposomes and with th e data we obtained in a previous study on a tissular model. This study demonstrates the interest of a laser-induced release liposome-encapsu lated dye for a real-time quantification of thermal damage. Such a met hod could be useful for laser photocoagulation in ophthalmology for in dications such as choroidal neovessels where the production of a preci se thermal damage is required.