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Kurs: MCAT > Rozdział 2

Lekcja 1: Biological sciences practice passage questions

How to remove a tattoo


In addition to its use in diagnosis, radiation has several applications for medical therapy. Most notably, radiation is used to target and treat inoperable cancers that are otherwise unresponsive to chemotherapy. Additionally, light amplification by stimulated emission of radiation (or more commonly known as L.A.S.E.R.) is a tool frequently used in surgical resection, dental procedures, refractive eye surgery, and cosmetic surgery.
When using lasers, the operator must consider three parameters: the wavelength of light, fluence (or amount of laser emitted), and the duration of the pulse. Commonly, the wavelength of a laser is fixed. Fluence and pulse duration, however, can be adjusted by the physician. The energy emitted by the laser is absorbed by a chromophore or particle that absorbs a specific wavelength of light. Careful balance of these three parameters is essential to accurately and selectively target chromophores while sparing the surrounding tissue. Lasers deliver a concentrated beam of energy to a chromophore resulting in photothermolysis where the heat produced from the transfer of energy will cause denaturation. Inadequate fluence or pulse will cause no effect while inappropriately high fluence or prolonged pulse can result in thermal injury to nearby structures or scarring.
To remove tattoos, Q-switched lasers are used to deliver high-intensity energy over a short period of time, usually picoseconds. Based on the absorption spectrum, certain wavelengths of light are employed for certain chromophores (Figure 1). Tattoo pigments have a variety of colors and therefore require lasers with specific wavelengths that allow for optimal absorption for photothermolysis. A physician selects a laser emitting light of a certain wavelength that yield a greater absorption coefficient to maximize absorption by the targeted chromophore to ensure optimal photothermolysis while minimizing damage to adjacent tissue. Tattoos with red pigment, for instance, are best removed using lasers emitting green light within the range of 492577 nm.
What is the most superficial layer of skin that tattoo pigment is most likely to remain embedded in the long-term?
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