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| Photoepilaton General Principles | ||
| To bring about successful long term hair removal, via selective photothermolysis, it is necessary to thermally damage the structures in the hair root responsible for hair growth, namely the papilla (bulb) and bulge. Thermal damage to the bulb and bulge occurs at approximately 74°C. The photothermal destruction of these two elements serves to prevent or significantly delay future hair growth | ||
| To raise the temperature inside the follicle, LHE uses the hair shaft as a conduit. Melanin in the hair shaft, as the targeted chromophore, absorbs the light which is then converted to heat inside the follicle. Normally, it requires a very intense light source applied to the skin to reach a sufficient temperature inside the follicle. LHE, however, overcomes this and significantly lowers the fluence by combining the light with a directed heat process. |
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| The advantages of lowering the energy fluence in hair removal are multifold, in addition to increased safety, LHE treatments can be applied on bare skin for example, without the need for cooling agents that make the process more complicated for the practitioner and less comfortable for the client. | ||
| Long Term Removal and Hair Growth Biology | ||
| Hair growth occurs in a three part cycle: anagen (active), catagen (transition) and telogen (resting). During anagen, the hair and follicle are active and there is an increase of melanin. Being that light based hair removal relies heavily on melanin for effectiveness, it is important that each hair and follicle be treated during this active phase to ensure maximum hair removal. As each hair on the body goes through this cycle independently, a course of treatments over a period of time will ensure that each hair and follicle is thermally damaged during its active growth phase. |
| Optimal Parameters for Clinical Efficacy |
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| For clinical efficacy LHE optimizes the parameters of wavelength range, pulse width and spot size. |
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When determining the appropriate wavelength for LHE hair removal, Radiancy scientists took several factors into consideration. First of all they were concerned with safety. Wavelengths at the lower, UV, end of the spectrum were eliminated as UV light has been theorized to cause lasting tissue damage.
Next was the issue of depth penetration. Since hair roots are found at depths of between 2mm to 4mm, depending on the body site, it was important to choose a wavelength range that would thermally damage roots at the deepest level. And lastly they factored in the absorption criteria of melanin. Melanin absorption of light peaks in the spectral range of between 300 and 800nm but continues to absorb well past 1000nm. |
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The convergence of these three parameters dictated a spectral range of 400nm to 1200nm. With this wavelength range, LHE is well within the safety threshold of the visible light spectrum yet still emits wavelengths for effective melanin absorption at depths up to and even exceeding 4mm.
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| Pulse Width | ||
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Pulse width is crucial to the safe application of light based treatment. The 35ms pulse width for LHE photoepilation was determined by balancing the Thermal Relaxation Time (TRT) of the hair shaft, follicle and epidermis. The TRT is time it takes for body tissue to cool to 50% of its heated state after thermal exposure. |
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When determining the appropriate wavelength for LHE hair removal, Radiancy scientists took several factors into consideration. First of all they were concerned with safety. Wavelengths at the lower, UV, end of the spectrum were eliminated as UV light has been theorized to cause lasting tissue damage.
Next was the issue of depth penetration. Since hair roots are found at depths of between 2mm to 4mm, depending on the body site, it was important to choose a wavelength range that would thermally damage roots at the deepest level. And lastly they factored in the absorption criteria of melanin. Melanin absorption of light peaks in the spectral range of between 300 and 800nm but continues to absorb well past 1000nm. |
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The convergence of these three parameters dictated a spectral range of 400nm to 1200nm. With this wavelength range, LHE is well within the safety threshold of the visible light spectrum yet still emits wavelengths for effective melanin absorption at depths up to and even exceeding 4mm.
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The TRT of the epidermis is 3-7ms, while the TRT of the hair shaft is 40-100ms. This means that sometime between 3ms and 7ms after the application of energy, the energy directed at the epidermis will have diffused sufficiently to protect the epidermis from overheating. The hair shaft, however, with its much longer TRT will continue to accumulate heat for an additional 30ms, before it too it will begin this cooling process and further heating will no longer be effective and will risk burns. A 35msec puls thus maximizes heating efficacy of the follicle while minimizing the risk of thermal damage to the epidermis. |
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| Spot Size | |
| The LHE spot size serves to further increase effectiveness and ease of use. When light photons are applied to the epidermis they no longer retain an organized pattern of proliferation but instead scatter throughout the dermis and epidermis. Subsequently light intensity is  subdued as photons are ‘lost’ by the scattering process as well as by diffusion. In order to minimize energy loss, LHE begins with a larger light source employed over a wider surface area.The large spot size reduces the percentage of photons lost due to side scattering and increases the depth penetration of the remaining photons. |
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