The interaction of light with skin

Abstract

The past thirty years have seen many advances in medicine. One of the most significant developments has been in the use of the laser. This instrument has been used in a number of surgical therapies including the removal of vascular lesions and the removal of tattoos. Lasers for the treatment of vascular lesions have progressed from early devices which ablated the skin surrounding the ectatic vessels and thus caused scarring, to devices which use selective thermolysis and leave the texture of the skin unchanged. Two such devices are the flash-lamp pumped pulsed dye laser and the copper vapour laser. This thesis investigates what is known about the processes that occur in the skin following the treatment of vascular lesions with these lasers. The purpura-like response of the pulsed dye laser is due to a stationary coagulum of erythrocytes in the treated vessels. The blanching caused by the copper vapour laser is less well understood. We photograph the treatment process, and quantitatively measure the light remitted from the skin. We conclude that blanching is caused by a combination of vasoconstriction, as proposed by Marini et al. (1992), and destruction of epidermal melanin. It is observed that light coloured vascular lesions blanch faster and require more energy to blanch than dark lesions. These phenomena are related to the smaller size of the ectatic vessels in light coloured lesions. The use of Q-switched ruby lasers for removal of tattoos has long been established. However such devices are expensive and are unable to remove red pigments. This thesis reports on progress made towards the development of a cheaper flash-lamp based system which might be able to remove all pigment colours.