New approaches to the laser treatment of vascular lesions

The pulsed dye laser (PDL) was developed based on the concept of selective photothermolysis. Using a wavelength of light well absorbed by the target and a pulse duration short enough to spatially confine thermal injury, specific vascular injury could be produced. While the PDL revolutionized the treatment of port wine stains (PWS) and a variety of other vascular lesions, the mathematical model predicted that the ideal thermal relaxation time for the vessels in PWS is actually 1-10 msec, not 450 microseconds. These original theoretical calculations have been proved correct recently in a study using both an animal vessel model and in human PWS. Longer wavelengths of light within the visible spectrum penetrate deeper into the skin and are more suitable for deeper vessels; while longer pulse duration is required for larger calibre vessels. A variety of lasers have been developed recently for the treatment of vascular lesions that incorporate these concepts into their design, including PDL at 1.5 msec, a filtered flash-lamp pulsed light source with pulse durations of 1-20 msec, several 532 nm pulsed lasers with pulse durations of 1 to as high as 100 msec, long pulsed alexandrite lasers at 755 nm with pulse durations up to 20 msec, pulsed diode lasers in the 800-900 nm range, and long pulsed 1064 Nd:YAG sources. Preliminary results are encouraging.