Dynamic cooling for laser photocoagulation: In vivo & ex vivo studies

When a cryogen spurt is applied to the skin surface for an appropriately short period of time (on the order of milliseconds), the cooling remains localized in the epidermis, while leaving the temperature of the deeper vessels of hemangiomas unchanged. The purpose of our study is to examine the effectiveness of dynamic cooling in protecting superficial tissue structures during continuous Nd:YAG laser illumination of in vivo and ex vivo models for hemangiomas. The bovine liver and highly vascularized chicken combs were selected as the models for hemangiomas. The Nd:YAG laser illumination ranged from 20 to 60 W. A feedback system utilizing infrared radiometry monitored the surface temperature and controlled delivery time of the cryogen spurt. When the surface temperature during laser illumination reached 36-45°C, a 30-100 m/sec cryogen spurt was delivered. Animals were observed 1 hour to 14 days following each experiment. Gross and histological analyses were performed. Nd:YAG laser illumination resulted in deep (up to 1.0 ± 0.2 mm) tissue photocoagulation, while dynamic cooling preserved the overlying epidermis and papillary dermis. In conclusion, dynamic cooling is effective in protecting the epidermis and papillary dermis, while achieving deep tissue photocoagulation during Nd:YAG laser illumination. This procedure is effective for the treatment of hemangioma in the humans.