EVLA works by means of thermal destruction of venous tissues. Laser energy is delivered to the desired incompetent segment inside the vein through a bare laser fber that has been passed through a sheath to the desired location.
Several wavelengths have been proposed: 810, 940, 0, 1,064, and 1,320 nm, with 810, 0, and 980 being the most commonly used. More cently, use of a 1,470- to 1,500-nm diode laser has en proposed. Wavelengths of 1,470–1,500 nm are eferentially absorbed by water.
When using laser light, heat is generated within the zone of optical penetration by direct absorption of laser energy. Absorption is the primary event that allows a laser or other light source to cause a poten-tially therapeutic (or damaging) effect on a tissue. Without absorption, there is no energy transfer to the tissue and the tissue is left unaffected by the light. Scattering of light occurs in all biological tissues: blood, vessel walls, and perivenous tissue. Due to fuc-tuations in the refractive index of these media, the propagation of light into the tissue is modifed and the scattering affects “where” the absorption will occur, usually reducing the penetration of light into the tissue.
Heating decreases with tissue depth as absorption and scattering attenuate the incident beam. Based on the absorption and effective scattering coeffcients of the biological tissue, the optical extinction (µeff) can be determined.
Absorption, reduced scattering and extinction coeffcients of blood, vessel wall, and perivenous tissue relative to wavelength
This table clearly shows that the optical extinction is much higher at 1,470–1,500 nm (5–9 times higher) compared to 810, 940, 980, and 1,320 nm. Interestingly, for these wavelengths, the optical extinction is similar for blood and vessel wall
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