Background and objective: The objective of this in vivo study was to assess the possible use of temperature-sensitive liposomes as a new approach 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: Temperature-sensitive liposomes (DSPC: Di-Stearoyl-Phosphatidyl-Choline) were loaded with carboxyfluorescein. These liposomes (1 ml solution) were injected into adult male Wistar rats. Two hours later, the liver was exposed and irradiated with a 100 W Nd:YAG laser using pulses lasting from 100 to 260 ms. Simultaneously, the surface temperature was recorded with a thermographic camera. The fluorescence emission was measured with a fluorescent imaging system.
Results: The results showed that the dye was released in response to laser energy. The amount of the drug release increased linearly with increasing temperature in the range 42-60 degrees C. Moreover, the release occurred in a short period of time upon brief exposure to its phase transition temperature.
Conclusion: 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 coagulation of biological tissues such as blood vessels.