Development of a broadband light source with variable pulse length and energy for the treatment of vascular lesions

Abstract

Currently the most commonly accepted treatment for port wine stains (PWS) is the process of selective photothermolysis using pulsed lasers. In principle light is absorbed by the blood heating the vessel walls leading to subsequent destruction. The wavelength should be chosen so that the light is absorbed well by haemoglobin, but not by the skin tissue. There is evidence to suggest that the pulse length should be chosen to match the thermal relaxation time of the blood vessels. For individual vessels this is around 10 ms or below. If we consider the whole PWS there are indications that pulse lengths greater than this may be more suitable and a range of pulse lengths may be required. Varying the pulse length with a laser can be difficult. With the development of intense white light sources, variations in wavelength, pulse width and fluence can be achieved and therefore allow versatility in selective photothermolysis treatment. The development of a prototype intense, filtered, white light source to treat PWS has been undertaken. A short-arc, Xenon filled lamp has been incorporated into a system whereby it is possible to have a modulated output of varying pulse-lengths (approximately 30 ms - 400 ms) and energies of 0.5 J - 2 J. The filtered (525 nm - 625 nm) light is delivered through a liquid light guide giving a spot size of 5 mm. This prototype has been developed, is being evaluated clinically, and could have the potential to treat a wide variety of vascular lesions (especially dense PWS) and yet be small, robust and inexpensive. A summary of the development, performance and initial trials is presented.