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

There are a wide variety of fractional resurfacing devices that are available and it is important to understand the tissue effect of different devices at different parameters to ensure a well-controlled treatment. Thus, we have chosen to characterize and compare two different fractional laser devices, the Fraxel SR750 and SR1500 (re:store) (Solta Medical, Hayward, CA). While the SR750 has a fixed focus spot diameter, the SR1500 features an internally controlled zoom optic allowing for an adjustable spot size.

Exposures were performed in vitro on human skin samples at 37 degrees C. The exposures were performed for the SR750 at pulse energies between 6 and 40 mJ at 125 MTZ/cm(2) with up to 20 passes, and for the SR1500 between 6 and 100 mJ, at Treatment Level 7 and 8 passes. The skin samples then were processed for serial frozen sectioning, stained with Nitro-Blue-Tetrazolium-Chloride (NBTC) and lesion depth and width was determined.

Mean lesion depth was significantly greater for lesions treated with the SR1500 laser compared to the SR750 at pulse energies of 6, 10, 30, and 40 mJ (P<0.001) with a borderline difference at 20 mJ. Mean lesion width was comparable for energies up to 20 mJ and relatively increased for the SR1500 for higher energies. The depth-to-width ratio (DWR) was in general higher for the SR1500, reaching significance at 6, 10, and 40 mJ.

We have characterized the lesion depth and width for the for two different Fractional Photothermolysis devices (SR750 vs. SR1500). The device with the adjustable spot size (SR1500 or Fraxel re:store) provides generally deeper lesions at the same energy level. It remains to be shown whether increased lesion depth improves efficacy for certain clinical applications.