Laser-Induced Release of Liposome-Encapsulated Dye: A New Diagnostic Tool

Abstract

This paper reviews applications of laser-induced release of liposome-encapsulated dye as a diagnostic tool. The technique consists of encapsulating a fluorescent dye into liposomes at high concentration. Before injection, liposomes are not fluorescent. After systemic liposome injection, a laser beam is used to increase the temperature at a specific site (blood vessel, biological structures, etc.). This increase of temperature causes leakage of liposomal content. The dye is released in the surrounding medium and then diluted, leading to the appearance of fluorescence. Recent experiments in animals have demonstrated that this technique could be used in ophthalmology for the simultaneous measurements of blood flow in the retinal arteries, veins and capillaries of the macula and optic nerve. Since many diseases of the retina result in changes in retinal circulation, information on haemodynamics can be important in the diagnosis of these diseases and the evaluation of current and new therapies. Similarly, laser-induced thermal damage can be quantified by this technique. In that particular case, the phase-transition temperature of the liposomes is adapted to the tissue temperature range. Since tissue thermal damage is unwanted, the laser wavelength is chosen to avoid any direct absorption of light by the dye entrapped into the liposomes. Different fluorescence images can clearly document tissue thermal damage depending on target (blood vessel or parenchyma) and energy deposition in tissue. One of the most significant applications of this experimental technique could be the evaluation of various degrees of tissue thermal damage. The application of this new diagnostic tool for general clinical practice would require consideration of the use of liposomes in humans.