Селективный фототермолиз
Laser beam applied to alive tissue have different effects on tissue components depend on absorption spectra. Main skin components absorbing the laser light are water, melanin and hemoglobin. They are called skin chromophores and have different absorption specters.
Absorption spectra of cutaneous chromophores: (1) – hemoglobin; (2) – oxyhemoglobin; (3) – melanin. Water absorbs a little in this part of spectra.
Let see the light absorption spectra of the cutaneous chromophores. Ultra violet light is strongly absorbed by melanin and a little absorbed by water. Yellow and green lights are notably absorbed by melanin and a little absorbed by water. Some wavelengths in green and yellow spectra are strongly absorbed by hemoglobin and oxyhemoglobin and therefor by blood vessels. Infra red light is absorbed by water, however melanin and hemoglobin almost not absorb it. Choosing the right wavelength we can affect on the target chromophore of the skin.
Choosing the wavelength in green-yellow spectra near the absorption maximum of hemoglobin and oxyhemoglobin we can remove abnormal cutaneous vessels (telangiactasias, port wine stains) without injuring of the surrounding tissue. This treatment is called selective laser coagulation based on the principle of selective photothermolysis first discovered by R.R. Anderson and J.A. Parrish. Laser skin resurfacing, laser removing of tattoos and laser removing undesired hair are based on this concept – thermal destruction of target without injuring of surrounding tissue.
Effectiveness of the treatment depends on the laser parameters such as:
- Wavelength – λ
- Laser power – P
- Laser light spot size: diameter d and square – S
- Exposition time – Т
- Fluence F = P*T/S
If parameters choused appropriately, the target chromophores destroyed selectively without injuring the surrounding tissue.
According to the concept of selective photothermolysis for removing abnormal blood vessel it’s necessary to meet some demands:
- laser wavelength must coincident with the yellow absorption pick of hemoglobin and oxyhemoglobin – 576 nm;
- laser light spot must compare with the diameter of abnormal vessels – about 0.5 mm;
- pulse duration must be smaller than thermal relaxation time of vessels;
- laser power must be sufficient to provide the effect of selective photothermolysis but no more
Note that the absorption picks of hemoglobin and oxyhemoglobin in blue spectra can’t be used for selective photothermolysis because the depth of laser light penetration in the blue is extremely short. Infra-red wavelengths also can’t be used because they are absorbed a little by hemoglobin and oxyhemoglobin.
Yachroma-Med the copper vapor laser system well satisfies all this demands. Thousands adults and children have been treated effectively with Yachroma-Med. Thus it has been shown that Yachroma-Med save and effective laser system for the treatment of cutaneous vascular lesion.
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