Tattoo Removal - Mechanism of Laser Action

Mechanism of Laser Action

Experimental observations of the effects of short-pulsed lasers on tattoos were first reported in the late 1960s. In 1979 an argon laser was used for tattoo removal in 28 patients, with limited success. In 1978 a carbon dioxide was also used, but generally caused scarring after treatments It was not until the late 1980s that Q-switched lasers became commercially practical. One of the first published articles describing laser tattoo removal was authored by a group at Massachusetts General Hospital in 1990.

Tattoos consist of thousands of particles of tattoo pigment suspended in the skin. While normal human growth and healing processes will remove small foreign particles from the skin, tattoo pigment particles are permanent because they are too big to be removed. Laser treatment causes tattoo pigment particles to heat up and fragment into smaller pieces. These smaller pieces are then removed by normal body processes.

Laser tattoo removal is a successful application of the theory of selective photothermolysis (SPTL). For laser tattoo removal, SPTL for the selective destruction of tattoo pigments depends on four factors:

• The color of the light must penetrate sufficiently deep into the skin to reach the tattoo pigment.
• The color of the laser light must be more highly absorbed by the tattoo pigment than the surrounding skin. Different tattoo pigments therefore require different laser colors. For example, red light is highly absorbed by green tattoo pigments.
• The time duration (pulse duration) of the laser energy must be very short, so that the tattoo pigment is heated to fragmentation temperature before its heat can dissipate to the surrounding skin. Otherwise, heating of the surrounding tissue can cause burns or scars. For laser tattoo removal, this duration should be on the order of nanoseconds.
• Sufficient energy must be delivered during each laser pulse to heat the pigment to fragmentation. If the energy is too low, pigment will not fragment and no removal will take place.

Q-switched lasers are the only commercially available devices that can meet these requirements.

Although they occur infrequently, mucosal tattoos can be successfully treated with Q-switched lasers as well.

A novel method for laser tattoo removal using a fractionated CO2 or Erbium:YAG laser, alone or in combination with Q-switched lasers, was reported by Ibrahimi and coworkers from the Wellman Center of Photomedicine at the Massachusetts General Hospital. This new approach to laser tattoo removal may afford the ability to remove colors such as yellow and white, which have proven to be resistant to traditional Q-switched laser therapy.