Laser-induced release of liposome-encapsulated dye: A new diagnostic tool

This paper reviews applications of laser-induced release of liposome-encaps ulated dye as a diagnostic tool. The technique consists of encapsulating a fluorescent dye into liposomes at high concentration. Before injection, lip osomes are not fluorescent. After systemic liposome injection, a laser beam is used to increase the temperature at a specific site (blood vessel, biol ogical structures, etc.). This increase of temperature causes leakage of li posomal content. The dye is released in the surrounding medium and then dil uted, leading to the appearance of fluorescence. Recent experiments in anim als have demonstrated that this technique could be used in ophthalmology fo r the simultaneous measurements of blood flow in the retinal arteries, vein s and capillaries of the macula and optic nerve. Since many diseases of the retina result in changes in retinal circulation, information on haemodynam ics can be important in the diagnosis of these diseases and the evaluation of current and new therapies. Similarly, laser-induced thermal damage can b e quantified by this technique. In that particular case, the phase-transiti on 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 liposom es. Different fluorescence images can clearly document tissue thermal damag e depending on target (blood vessel or parenchyma) and energy deposition in tissue. One of the most significant applications of this experimental tech nique could be the evaluation of various degrees of tissue thermal damage. The application of this new diagnostic tool for general clinical practice w ould require consideration of the use of liposomes in humans.