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Selective Photothermolysis
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.
Picture 1.
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 –  ,
Laser power – P,
Laser light spot size: diameter d and square – S,
Exposition time – ̉,
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.
O. Ponomareva
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Yachroma-Med treatment
of vascular lesions:
Hemangioma before and after one Yachroma-Med treatment.
Dr. Andrei
Rogozhin, Centro de laser, Quito, Ecuador.
Nasal teleangiectasias before and after Yachroma-Med treatment.
Dr. Andrey Burov, Odessa, Ukraine.
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