microvasculature, hấp thụ các photon, các thiết bị tần số vô tuyến cung cấp một dòng điện nonselectively tạo ra nhiệt bởi sức đề kháng tự nhiên của các mô để dòng chảy của ion. Khi hấp thụ melanin không phải là một vấn đề, | 120 Tina S. Alster Seema Doshi 7 Fig. b. Perioral rhytides in a patient with skin phototype II before a and after b the third nonablative 1 320 nm Nd YAG laser treatment microvasculature absorb photons the radiofrequency device delivers an electric current that nonselectively generates heat by the tissue s natural resistance to the flow of ions. As melanin absorption is not an issue this RF device can be safely applied regardless of skin type. Radiofrequency technology has previously been used for aesthetic cutaneous surgery albeit for a limited time and with equivocal results. High frequency low voltage energy was delivered through conducting media for epidermal ablation cold ablation 69 70 . Reconfiguration of this technology resulted in the ThermaCool TCtm System Thermage Inc. Hayward CA which has a unique treatment tip with a coupled electrode design that allows for uniform volumetric heating of the deep dermis. To prevent epidermal ablation cryogen spray cooling is delivered prior to during and after the emission of radiofrequency energy. Laser Skin Resurfacing Chapter 7 121 Fig. b. Atrophic acne scars in a patient with skin phototype III IV before a and after b three consecutive monthly nonablative long-pulsed 1 450-nm diode laser treatments Heating of the deep dermis and subcutaneous tissue occurs with the depth determined by treatment tip geometry and the impedance levels in varying tissues as opposed to wavelength with laser irradiation . Heat-induced collagen denaturation and contraction account for the immediate skin tightening seen after treatment 67 . As with all other non-ablative devices further neocollagenesis takes place over the ensuing months effecting further reduction of rhy- tides and tissue tightening 71-74 . Periocular rhytides and brow rhytides have shown significant improvement after a single treatment as have cheek and neck laxity 71-74 . Maximal clinical results are observed 3 to 6 months after treatment and additional .
