Infrared imaging of CO₂ laser ablation: Implications for laser skin resurfacing

Surface temperature measurements and CCD video imaging were performed during multiple pulse irradiation on in vivo rat skin. A TruPulse laser (100-μs pulsewidth, 3 mm × 3 mm spot size) was used at radiant exposures of 2.4 J/cm² and 3.9 J/cm² for all experiments. Temperatures were recorded with a thermal camera. During multiple pulse irradiation, one pulse per second was applied to a single site. A total of fifteen pulses were applied to a single spot. Irradiating with 2.4 J/cm² pulses led to a slow temperature rise that reached steady state at approximately 200°C. Carbonization onset occurred after pulses 5-8. With a higher radiant exposure of 3.9 J/cm², carbonization occurred after the third pulse; after the tenth pulse, focal tissue burning was visible, and the temperature oscillated around 350°C. Surface temperatures were measured during clinical scans. Areas of 3 cm × 3 cm were treated by the laser, which was moved across the tissue in a raster scan with 8 pulses per second. Each area was treated three times. From analysis of histological sections, the thermal damage as a function of pass number and radiant exposure was noted. Contrary to previous reports, the epidermis was not removed after the first pass. Indeed, after three passes, the epidermis was still present (H_o = 2.4 J/cm²) or was severely fragmented (H_o = 3.9 J/cm²).