田艳丽医生分享：射频美容技术ppt课件.ppt

换能器必须紧贴皮肤！不然，换能器无法将HIFU能量传输至指定的目标组织，无法达到预期的效果。甚至，还有可能会造成不可预料的副作用！ * Heat is generated based on tissue’s natural resistance to the movement of electrons within an RF field (Ohm’s law), not photon absorption. This is referred to as “resistive” heating. Ohm’s Law: Impedance Z (ohms) to the movement of electrons creates heat relative to the amount of current I (amps) and time t (seconds). * This chart shows the relative depths of energy penetration of various light sources compared with the 1.5cm2 medium-depth ThermaTip.? At the surface of the skin, all the energy sources have 100% of their initial intensity.? Light energy is absorbed and/or scattered as it travels deeper into the tissue, so the energy density decreases. Light energy is absorbed according to Beer’s Law, which governs how energy intensity decreases as it passes through an absorptive medium. Thus, yielding a steep exponential decline in intensity.? The 1/e depth is the depth at which the intensity decreases to 37% of its surface intensity.? Note the 1/e depth for CO2 is about 50 microns, and about 1,000 microns for 1320nm.? Note that 1320 wavelength is one of the deepest-penetrating water-targeting wavelengths.? Infrared (IR) sources like Cutera Titan, Candela GentleYAG (Nd:YAG 1064 nm), or Orion Harmony (Nd:YAG 1064 1320 nm) are probably somewhere below the blue line.? RF electric fields conform to Maxwell’s equations which dictate how?RF energy intensity is reduced as it travels further from the electrode surface producing a gradual decline in intensity. As you can see by the intensity-versus-depth curve for Thermage, its 1/e depth is at 2.5mm--much deeper than any of the light sources.? This model assumes that all the tissue is homogeneous dermal model with no fat.? If this were real tissue, Thermage RF would selectively heat fibrous septae much deeper into the subcutaneous tissue. Body impedance is ~300 ohms, minimum reflection is from 50 ohms Above 50 ohms causes reflection Less power reaches b