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INTRODUCTION

Lasers have been used clinically by physicians and surgeons for decades. The use of lasers in the operating rooms and offices of aesthetic plastic surgeons, however, surged in the mid-1990s. This coincided with the introduction of carbon dioxide (CO2) lasers as an alternative to chemical peels and microdermabrasion. Since that time, plastic surgeons have seen the numbers of lasers and intense pulse light (IPL) devices introduced into the aesthetic market place expand exponentially as the field has advanced both clinically as well as technically. Lasers and IPL devices are used today not only to resurface or smooth skin but also to tighten and rejuvenate the texture and pigmentation of the skin of the face and neck as well as the other parts of the body.

APPROPRIATE LASER SELECTION

Selecting a laser requires choosing the proper wavelength of light as well as paying attention to multiple other parameters such as energy and pulse duration, to achieve the desired clinical effect with minimal complications. This selection is based in part on the basic tenets of the theory of selective photothermolysis.

The first tenet explains that the wavelength of light must be selectively absorbed by the target tissue. For example, the target of the laser surgeon who wishes to treat hirsutism is melanin. Lasers that emit light in the range selectively absorbed by melanin, which include the alexandrite (755 nm), the ruby (694 nm), and the diode (810 nm) wavelength lasers, would be appropriate choices.

The second tenet explains that the energy of the laser light must be of a high enough energy to destroy the target tissue.

Finally, the laser must produce sufficient energy to destroy the target without damaging the surrounding structures. In other words, if the laser generated so much heat in destroying the hair follicle that the surrounding skin blistered and scarred, the clinical result would obviously be unsatisfactory.

In order to achieve destruction of the target tissue, the target must be heated faster than the rate that the heat dissipates. This rate is defined as the thermal relaxation time of tissue (TRT). The TRT is a measurement of how long it takes for any tissue or structure to lose half the heat put into it by a laser or other heat source.

LASER–TISSUE INTERACTION

When light is directed onto the surface of the skin, the light is transmitted, reflected, scattered, or absorbed. Achieving the desired clinical or therapeutic effect requires an understanding of the laser-tissue interaction as well as the spectral absorption properties of the tissue being targeted. The three types of laser tissue interactions include photothermal, photoacoustic, and photochemical.

Photothermal effects represent the most common type of laser-tissue interaction clinically encountered in aesthetic treatments. The laser light is selectively absorbed by the chromophore, or target. The energy in ...

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