June 18, 1999 Mikhail Gorbachev was probably not greatly troubled by the "port wine stain" on his forehead, or perhaps he had no faith in the available treatments. Nevertheless, one in three of such birthmarks can be effectively treated using a laser. As part of a project funded by the NWO's Technology Council (STW), physicists at the University of Amsterdam have been able to improve the method considerably by increasing the wavelength of the laser light by a few nanometres, making it redder and able to penetrate better.
About 1% of normal skin consists of blood vessels. "Port wine" birthmarks have far more blood vessels than normal and the diameter of these vessels is also much greater. This gives the characteristic port-wine colour. This type of skin abnormality can be treated using photo-selective thermolysis, during which the area is irradiated with laser light of a particular colour; this is absorbed well by the blood but not by the rest of the skin. The light energy absorbed is converted into heat, which causes the blood vessels to shrivel up. After a period of healing, the area treated looks more like the surrounding normal skin.
The Dutch physicists developed a model enabling them to mimic the effect of various different types of laser light. They found that laser light at the wavelength of 585 nanometres currently used could hardly reach the centre of the large blood vessels. By choosing a slightly different colour, for example 590 nanometres, the deeper blood vessels were also accessible, without damage being done to the rest of the skin tissue. It should be noted that some 20% to 30% of "port wine" birthmarks are still not amenable to laser treatment, or only to a very limited extent, and treatment is sometimes painful, lengthy and expensive.
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