Effects of skin temperature on lesion size in fractional photothermolysis

Abstract

Background and Objectives: Fractional photothermolysis is a new concept in cutaneous re-modeling whereby laser-induced microscopic zones of thermal injury (MTZMicroscopic Treatment Zones) are surrounded by normal, viable tissue. This unique thermal damage pattern allows re-epithelialization in less than 24 hours. To increase patient comfort level during the procedure of fractional photothermolysis, simultaneous skin cooling has been proposed and is now extensively used. The purpose of this in vitro study was to examine the influence of skin temperature on the diameter of the epidermal microthermal zone and the extent of thermal injury per unit area. The determination of the changes in these parameters that are due to skin temperature will allow the better control and understanding of fractional photothermolysis at different skin temperatures. Materials and Methods: Fractional photothermolysis was performed with a 1,550 nm fiber laser (Fraxel SR 1 Laser) with 10 mJ per pulse on full-thickness cadaver skin. The skin samples were brought prior to exposure to temperatures that ranged from 0 to 458C. The epidermis of the skin samples was separated by dispase treatment, stained for thermal damage by NBTC stain, and lesion diameter was assessed by a blinded investigator. Results : The average MTZ diameter exhibits a positive, linear relationship with skin temperature (R 2 ¼ 0.904, P < 0.0001). As the skin temperature increases from 0 to 458C. The MTZ diameter increases from 93 to 147 mm (58%), and the MTZ area from 6,870 to 17,050 mm 2 (148%). Conclusion : The skin temperature affects the size of epidermal MTZs during fractional photothermolysis and is an important variable factor. The use of simultaneous skin cooling increases patient comfort; however, as it also decreases MTZ size, it may interfere with treatment efficacy. The control of skin temperature is necessary to provide a consistent outcome and to be able to compare treatments.

Histological comparison of two different fractional photothermolysis devices operating at 1,550 nm

“…In terms of bulk heating, as we have provided multiple passes on the majority of the samples (up to 20), we have paid close attention to minimize the effects of rising tissue temperature [21] and to avoid confluent thermal damage (bulk heating). Therefore, we have selected for the SR750 the lowest MTZ density per pass (125 MTZ/cm 2 /pass), applied a delay in between passes and have measured the skin surface temperature using a thermocouple after each pass.…”

“…However, as skin surface temperature affects lesion diameter [21] and air cooling is used in a clinical setting there is likely some variation of the in vitro determined lesion diameter as compared to the in vivo use. The effects of superficial skin cooling on lesion depth are not known but based on the temperature gradient rising after skin cooling, it can be expected that the lesion depth is less affected by superficial skin cooling.…”

Fraktionierte Photothermolyse

“…Insgesamt werden bei der FP 10-20% der Hautfläche zerstört [25]; die Tiefe der Läsi-onen hängt in erster Linie von der Energiedichte der Laserimpulse, aber auch von der Hauttemperatur [26] ab und kann individuell angepasst werden [14,25,29,33,55].…”

Resolution of blue minocycline pigmentation of the face after fractional photothermolysis

“…Additionally, bulk heating may result from treating a small area with multiple passes without allowing sufficient time to cool. This may lead to scarring [13][14][15].…”