▶ Previous Artlcle: #2-2. Basics of LASER

 

Laser-Tissue Interactions

 

Once a tissue to be treated is irradiated by the laser, an interaction occurs between photon of the irradiating laser and the tissue, which is called tissue optics or laser-tissue interaction. The laser tissue interaction includes reflection, scattering, absorption, and transmission.

 

First, when it comes to reflection, the released photons bounce off a tissue surface instead of passing through it, like a ball thrown against a wall. Generally, 4 to 7% of the released photons is reflected. Second, scattering means that the photon entering the tissue scatters around as they meet another tissue, which becomesan obstacle, before reaching the target tissue.

 

Whether or not the released photon energy will effectively reach the target tissue depends on the degree of scattering. Third, absorption refers to having photothermal, photomechanical, and photochemical effects, etc. as the released photon energy is delivered to the target tissue.

 

Thus, the results intended to be achieved after laser irradiation to the tissue are determined by absorption. Fourth, transmission refers to the photon energy just passing by, not absorbed into, the target tissue.

 

[Ad. ▶ COPPER BROMID(Yellow/Green Laser) – Manufacturer: BISON(www.bisonmedical.com)]

 

Chromophore

 

Once a tissue is irradiated by the laser, there are chromophores that are well absorbed per wavelength. The target chromophores during laser procedures include melanin, hemoglobin, protein, water, and tattoo ink.

 

The first step for treating a lesion is to consider which chromophore the lesion intended to be treated has and to choose a laser of the corresponding wavelength. In the case of treating freckles, for instance, it is possible to choose lasers at a wavelengthof 532nm, 694nm, 755nm or 1064nm with melanin as a chromophore because freckles are a lesion with an accumulation of melanin.

 

However, even if lasers have the same melanin as a chromophore, there are differences in absorbance and depth of penetration per wavelength. Therefore, the parameters using spot size and fluence of laser beam respectively are different depending on wavelength, lesion depth and thickness, and pigment density.

 

- To be continued