Imaging of the irradiation of skin with a clinical CO₂ laser system: Implications for laser skin resurfacing

Background and Objective: Several published reports describe the benefits of using the carbon dioxide laser for cutaneous resurfacing. The mechanisms on which skin resurfacing work are still not completely understood. This study was performed to obtain quantitative and qualitative information describing the thermal response of skin during high-energy, short-pulsed CO₂ laser irradiation. Study Design/Materials and Methods: A Tissue Technologies TruPulse CO₂ laser was used to irradiate an in vivo rat model. The laser parameters that were used were a 100-μs pulsewidth, a 1-Hz repetition rate, a 3 mmx 3 mm square spot size, and 2.4 J/cm² and 3.9 g/cm² radiant exposures. A 3-5 μm thermal camera was used to obtain temperature information during irradiation. Single spots were irradiated with one pulse, and the temperature-time history was obtained. In a different experiment, 15 pulses were applied to single spots, and both thermal and video images were obtained. Results: Irradiation with one pulse at 2.4 J/cm² and 3.9 J/cm² led to peak temperatures >100°C. The temperature relaxation time was -25- 150 ms. Multiple-pulse irradiation at 2.4 J/cm² led to a slight rise in the peak temperature with each pulse. At 3.9 J/cm², the peak temperature increased with successive pulses until pulse 10, after which the peak temperature oscillated between 300 and 400°C. Video images showed concurrent burning events that occurred during pulses 10-15. Conclusion: Temperatures >100°C were measured during CO₂ laser irradiation of skin. Pulse stacking can lead to peak temperatures approaching 400°C and to tissue charting with as few as three stacked pulses. It is crucial for the physician to manipulate the laser handpiece at parameters with which he or she can avoid pulse overlap.