Scanned continuous wave CO2 laser resurfacing: A closer look at the different scanning modes

BACKGROUND. The immediate effects of CO2 laser resurfacing include tissue a blation and residual thermal damage. These laser-tissue interactions are sh aped by parameters including fluence, dwell time, and number of passes. OBJECTIVE. To assess the vaporization depth and residual thermal damage fol lowing use of the "superficial" or "deep" scanning modes of a 40 W continuo us wave CO2 laser using both frozen and paraffin sections. METHODS. Fourteen subjects were divided into two groups for test treatments in the right preauricular area with two passes of the laser. The "superfic ial" mode parameters were 10 mm(2) scan, 200 mm lens, power 36 W, scan time 0.24 seconds, dwell time 0.22 msec, and fluence 5.5 J/cm(2). The "deep" mo de settings were 9 mm(2) scan, 200 mm lens, power 18 W, scan time 0.64 seco nds, dwell time 0.28 msec, and fluence 7.0 J/cm(2). The deep mode has a gre ater pattern density than the superficial mode and also has a double patter n of exposure. Biopsies encompassing equal areas of treated and untreated s kin were taken immediately postoperatively and processed with both frozen a nd paraffin-embedded techniques. RESULTS. Vaporization depth was similar in both scanning modes and by both tissue-processing techniques. On frozen sections, residual thermal damage w as 20% greater in the deep mode than the superficial mode, but this was not a statistically significant difference. There was no significant differenc e between the two modes in the depth of thermal injury on paraffin sections . CONCLUSION. In keeping with theoretical expectations, vaporization depth wa s similar in both treatment groups. No significant difference in residual t hermal damage could be demonstrated between the two modes. However, the res ults on frozen sections suggest that residual thermal damage may be greater in the deep mode than in the superficial mode. In addition, frozen section s may be more sensitive than paraffin sections in the detection of residual thermal damage following laser resurfacing.