Laser‐induced release of liposome‐encapsulated dye to monitor tissue temperature: A preliminary in vivo study

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Abstract
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°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.