Page 81 - An Introduction to Laser Tattoo Removal

Chapter 2 – Fundamentals of Laser Tattoo Removal v1.0
Fluence can be thought of as the ‘concentration’ of the laser energy in a spot. So, a small spot will have a high concentration (high fluence), while a larger spot, with the same applied energy, will result in a much lower concentration.
The choice of fluence is relatively simple. Always start ‘low’!!! The aim of the fluence is to ‘inject’ just enough energy into the tattoo ink to induce the desired response. Any excess fluence will merely cause unwanted thermal damage in the surrounding dermis. To see how to do this correctly, read the section ‘The Ideal Protocol’.
As the number of treatments increases, the fluence will need to be increased to account for the greater depth at which the ink will be found (see next section – ‘Anisotropy’). However, the fluence should ALWAYS be increased marginally, preferably by 0.5 J/cm2 increments!
An excellent study by Shreibner (1990) showed clearly that even a low fluence can stimulate a reaction in black ink tattoos. ‘Frosting’ appeared in most cases between 2 and 3 J/cm2, while there was very little response below 2 J/cm2.
Anisotropy
An often over-looked, yet important, issue when discussing laser tattoo removal is the anisotropy in the skin, for each wavelength.
When light enters the skin it immediately starts to ‘scatter’. This process causes the photons to deviate from their original direction, causing the beam spot diameter to ‘spread out’. As a direct consequence, the fluence drops, as the light energy penetrates deeper into the skin! What does scattering look like?
Here is an animation describing the effects of anisotropy on the four main laser tattoo removal wavelengths. As a consequence, green light from the 532nm wavelength cannot penetrate as far into the dermis as the red wavelengths of the ruby, alexandrite and fundamental Nd:YAG lasers.
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Chapter 2 LEVEL A Laser Tattoo Removal
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