Comparison of the Cutaneous Thermal Signatures Over Twenty-Four Hours With a Picosecond Alexandrite Laser Using a Flat or Fractional Optic
November 2016 | Volume 15 | Issue 11 | Original Article | 1347 | Copyright © 2016
Emil A.Tanghetti MDa and Danielle M.Tartar MD PhDb
aCenter for Dermatology and Laser Surgery, Sacramento, CA bUniversity of California, Davis, CA
INTRODUCTION: This study explored immediate heat signatures with different passing techniques and the delayed thermal data points with the picosecond Alexandrite laser with the 6mm at and fractional optic during and after treatment. We sought to clarify the im- mediate effects of heating and understand the thermal and short term clinical difference when using these optics. RESULTS: There were no immediate differences or a signi cant temperature rise with different passing techniques using the at or the fractional optic. However, after treatments a signi cant temperature elevation over 24 hours with manageable erythema was noted with the fractional optic. Only faint redness was appreciated with the at optic. CONCLUSION: The different passing methods with these optics did not result in a significant thermal change. However, the fractional optic produces a localized area of epidermal necrosis which results in a significant clinical and a delayed thermal effect. With multiple treatments over time, collagen, elastic tissue, and mucin is produced resulting in improvement of acne scars and photo-damaged skin. This process suggests that a well-placed epidermal injury can stimulate an inflammatory cascade with dermal remodeling. J Drugs Dermatol. 2016;15(11):1347-1352.
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Picosecond devices were commercially introduced a number of years ago to better treat tattoos and pigmented lesions. The picosecond Alexandrite laser effectively treats most tattoos. Difficult to treat green ink shows the most dramatic rapid clearing with this device. The absorption of 755 nm light by melanin also makes this laser an excellent treatment for Nevus of Ota and other pigmented lesions.The fractional optic was introduced for use in facial rejuvenation, abnormal pigmentation, and acne scars. Brauer and colleagues reported improvement in acne scars associated with new collagen, tissue and melanin after a series of treatments.1 Our center was the first to characterize the histological changes induced by this fractional optic. We observed intra-epidermal vacuoles located in the stratum granulosum of the epidermis measuring approximately 60 microns in diameter.2, 3, 4This localized zone of intra-epidermal injury was observed in individuals who had a melanin index (MI) of greater than 15, as measured by skin pigmentation meter (Skintel™) and who were skin type II or greater. This correlates with an individual who has some degree of epidermal pigmentation. We postulated that this injury is the result of laser induced optical breakdown (LIOB).4 This fractional delivered laser energy light appears to be absorbed by melanin creating a situation where one or more free electrons are generated (Figure 1). The number of free electrons grows in an avalanche process. A plasma region is created which absorbs energy from the laser pulse. The localized area of plasma generates heat to create a localized steam bubble. Histology taken within minutes after treatment reveals a vacuole created by the damage (Figure 2). There is very little damage noted by microscopy to the surrounding keratinocytes. At 24 hours, this void is filled with rehydrated (Figure 3) cellular debris which stains positively with Fontana Mason indicating the presence of melanin (Figure 4) Over the next three weeks the vacuole contracts and forms a zone of microscopic epidermal necrotic debris (MENDS), which is exfoliated (Figure 2).In low melanin individuals with skin type I and II, there is a different clinical picture and histology. Scattered hemorrhagic papules are sometimes seen with the highest energy settings. Histology reveals scattered areas of dermal hemorrhage often associated with vacuoles filled with red blood cells at the dermal/epidermal junction suggesting absorption of this high energy light by hemoglobin.4This device has been safely and effectively used for facial rejuvenation and acne scars in darker skin types. These epidermal vacuoles are seen with all commercially available spots 6mm (.71J/cm2), 8mm (.40J/ cm2), and 10mm (.25J cm2). The size of these vacuoles decreases as the energy decreases with the use