In-Service Exam
Laser - 2003





Which of the following characteristics of the carbon dioxide laser best explains the greater level of peripheral dermal injury that occurs with this laser than with the Er:YAG laser?

(A) Decreased thermal diffusion
(B) Less collagen contraction
(C) Limited coagulative necrosis
(D) Lower affinity for water
(E) Shorter pulse duration
The correct response is Option D.

Although the carbon dioxide and Er:YAG lasers are both absorbed by water, the Er:YAG laser has an affinity for water that is ten times greater than the carbon dioxide laser. It has an efficient rate of absorption and a short duration of exposure; each pass of the laser results in only minimal tissue necrosis. In addition, the pulse duration of the Er:YAG laser is shorter. Because it produces limited coagulative necrosis, the effect of erbium is photomechanical, rather than photothermal, and the amount of collagen contraction is much less than that produced by the carbon dioxide laser. Although the Er:YAG laser is well suited for fine ablation of the epidermis, it does not stimulate continued collagen remodeling.

In contrast, the carbon dioxide laser produces a greater thermal effect on surrounding tissue and subsequent collateral injury, resulting in continued remodeling of collagen and a greater overall cosmetic improvement.

References
1. Alster TS, Lupton JR. An overview of cutaneous laser resurfacing. Clin Plast Surg. 2001;28:37-52.
2. Weinstein C, Scheflan M. Simultaneously combined Er:YAG and carbon dioxide laser (derma K) for skin resurfacing. Clin Plast Surg. 2000;27:273-285.

A 17-year-old girl wishes to undergo removal of a butterfly-shaped tattoo that was professionally drawn in black ink on the skin overlying the right scapula. Which of the following lasers is most appropriate for removal?

(A) Carbon dioxide
(B) Copper vapor
(C) Erbium
(D) Nd:YAG
(E) Pulsed dye

The correct response is Option D.

The Nd:YAG laser is most appropriate for removal of this patient's tattoo. This laser emits light at a wavelength of 1064 nm and is preferentially absorbed by dark pigments, such as blue and black. It penetrates the skin to a depth of 2 to 6 mm, which will result in disruption of the tattoo pigment. Multiple treatments are typically required.

Both carbon dioxide and erbium lasers are inappropriate for tattoo removal because they are chromophores of water. These lasers are typically used to resurface scarred or wrinkled areas of skin. The carbon dioxide laser emits light at a wavelength of 10,600 nm and can be used in a continuous mode to cut skin. The erbium laser emits light at a wavelength of 2940 nm.
The copper vapor and pulsed dye lasers produce light at wavelengths from 500 to 600 nm. Although their beams penetrate skin, their shortened wavelengths preclude deep penetration. These laser wavelengths are absorbed by red and brown chromophores.

References
1. Apfelberg DB, Manchester GH. Decorative and traumatic tattoo biophysics and removal. Clin Plast Surg. 1987;14:243.
2. Kilmer SL, Lee MS, Grevelink JM, et al. The Q-switched Nd:YAG laser effectively treats tattoos. Arch Dermatol. 1993;129:971.
3. Levine VJ, Geronemus RG. Tattoo removal with the Q-switched ruby laser and the Q-switched Nd:YAG laser: a comparative study. Cutis. 1995;55:291.

In a 5-year-old child who has a large capillary vascular malformation on the upper eyelid, which of the following lasers is most appropriate for removal?

(A) Alexandrite
(B) Carbon dioxide
(C) Nd:YAG
(D) Pulsed dye
(E) Q-switched ruby

The correct response is Option D.

Removal of the capillary vascular malformation, or port-wine stain, is best accomplished with use of a flashlamp-pumped pulsed dye laser. This laser delivers short pulses (450 msec) of 585 nm of yellow light that are selectively absorbed by hemoglobin and oxyhemoglobin chromophores. Multiple treatments will result in ablation of the malformation.

Vascular lasers and other pigment-specific lasers function according to the principle of selective photothermolysis, which describes the resultant localized tissue damage. Target tissue damage occurs when light of a particular wavelength is delivered to and absorbed by the target, but not the surrounding tissue, during a pulse duration less than or equal to the thermal relaxation time of the target.

Carbon dioxide lasers act to vaporize water within the tissues. The mechanism of these lasers is similar to chemical peeling and dermabrasion and is inappropriate for port-wine stains.

At 1064 nm, the Nd:YAG laser is outside of the absorbable spectrum for hemoglobin; therefore, this laser is not recommended for the treatment of port-wine stains.

References
1. Alster TS. Manual of Cutaneous Laser Techniques. 2nd ed. Philadelphia Pa: Lippincott Williams & Wilkins; 2000:33-51.
2. Grossman MC, Kauvar AN, Geronemus RG. Cutaneous laser surgery. In: Aston SJ, Beasley RW, Thorne CH, eds. Grabb & Smith's Plastic Surgery. 5th ed. Philadelphia, Pa: Lippincott-Raven; 1997:205-219.