Laser-assisted hair transplantation:: Histological comparison between Holmium:YAG and CO2 lasers

The histological effects of flash-scanned CO2 (lambda=10.6 mu m) and pulsed Holmium:YAG (Ho:YAG, lambda=2.12 mu m) lasers were evaluated in human scalp following the creation of hair transplant recipient channels. Ho:YAG laser irradiation created larger zones of thermal injury (superficial de-epitheliazation, thermal necrosis, and thermal damage) adjacent to the laser channels than irradiation with the CO2, laser device. When the two lasers created recipient sites of nearly equal depth, the Holmium:YAG laser caused a larger region of lateral thermal damage (589.30 mu m) than the CO2, laser (118.07 mu m). In addition, Holmium:YAG irradiated specimens exhibited fractures or discontinuities beyond the region of clear thermal injury. This shearing effect is consistent with the photoacoustic mechanism of ablation associated with pulsed mid-IR laser irradiation. In contrast, channels created with the CO2 exhibited minimal epithelial disruption and significantly less lateral thermal damage. While the Holmium:YAG laser is a useful tool for ablating soft tissue with minimal char in select applications (sinus surgery, arthroscopic surgery), this study suggests that the use of the CO2 laser for the creation of transplantation recipient channels results in significantly less lateral thermal injury for the laser parameters employed.