A model approach to laser coagulation of dermal vascular lesions

The quantitative absorption of light by blood and by human skin is discussed in relation to laser coagulation therapy of dermal vascular lesions. The skin is represented by epidermis and dermis. Both layers are assumed to be planparallel. Absorption and scattering of light by turbid materials was accounted for by the Kubelka theory. Reflection and transmission data of blood and of skin were taken from the literature. This model shows that, firstly, argon-laser coagulation at 488/514.5 nm of dermal vascular lesions is a selective method because vascular absorption exceeds non-vascular dermal absorption by a factor of 10. Secondly, a coagulation depth of about 1 mm is predicted in agreement with the literature. Thirdly, the epidermis absorbs the 488/514.5 nm wavelengths about half as strong as blood and is therefore non-transparent. The consequences of this have been discussed in relations to the final cosmetic result. Fourthly, there is theoretical evidence that better cosmetic results may be expected when coagulation is performed at either 420 nm, 540 nm, or 575 nm. This suggests application of the krypton-laser with lines at 407, 413, and 415 nm (violet), at 531 nm, or at 568 nm. The krypton 647 nm line and the ruby 694 nm line are of little value for this purpose.