LASER-INDUCED RELEASE OF LIPOSOME-ENCAPSULATED DYE TO MONITOR TISSUE TEMPERATURE - A PRELIMINARY IN-VIVO STUDY

Background and Objective: The objective of this in vivo study was to a ssess the possible use of temperature-sensitive liposomes as a new app roach to monitor the temperature induced by a laser. Study Design: An in vivo/ex vivo study was performed in rat liver after i.v. injection of liposomes loaded with a fluorescent dye. Materials and Methods: Tem perature-sensitive liposomes (DSPC: Di-Stearoyl-Phosphatidyl-Choline) were loaded with carboxyfluorescein. These liposomes (1 ml solution) w ere injected into adult male Wistar rats. Two hours later, the liver w as exposed and irradiated with a 100 W Nd:YAG laser using pulses lasti ng from 100 to 260 ms. Simultaneously, the surface temperature was rec orded with a thermographic camera. The fluorescence emission was measu red with a fluorescent imaging system. Results: The results showed tha t the dye was released in response to laser energy. The amount of the drug release increased linearly with increasing temperature in the ran ge 42-60 degrees C. Moreover, the release occurred in a short period o f time upon brief exposure to its phase transition temperature. Conclu sion: The feasibility of temperature monitoring by using laser-induced release of liposome-encapsulated dye was demonstrated. This procedure could conceivably prove useful for controlling the thermal coagulatio n of biological tissues such as blood vessels. (C) 1995 Wiley-Liss, In c.