Optical Characterization Of The Aging Skin And Monitoring The Process Of Its Treatment

Cutaneous aging is a complicated biological process affecting different constituents of skin, which can be divided into two types:the chronological aging and the photo-aging. The former is also called an intrinsic aging process, which affects the skin by slow but irreversible degeneration. While the latter is known as an extrinsic aging process resulted from the exterior factors, such as the sun-exposed ultraviolet irradiation. The above two cutaneous aging processes often co-exist accompanying with each other. The effects are often overlapped including changes in epithelium and dermis. The degeneration of collagen, a main component in dermal extra-cellular matrix, is a major factor in dermal alteration with aging. In the dissertation, we combined the multiphoton microscopy (MPM) and optical coherence tomography (OCT) to study the two process of aging in vivo. It was the first attempts to make the optical parameter, morphological, spectrum and the texture feature to evaluate the process of two type aging and their treatment. The new evaluation feature was firstly introduced to uncover the different of two types aging in mechanism. Then the methods were applied to study the process of photo-thermal response in different laser source irradiated skin.The main results as follow:1. Multiphoton microscopy and optical coherence tomography were used to monitor the changes of morphology and spectrum in collagen during the process of chronological aging and photoaging in vivo. The result showed that the collagen dimension was nearly unchanged with ages. While the intensity of collagen in dermis was changed greatly with ages, the same as the detectable depthness in two types aging skin.2. It was the first to take the collagen texture features as one of the methods for evaluation of different types aging skin. Such as collagen orientation index, collagen bundle packing, collagen correlation, collagen entropy, and fractal dimension which were extracted from collagen structure. The results demonstrated that the collagen orientation index was small in younger stages skin. It indicated that the collagen alignment had more isotropic behavior. And the collagen bundle packing is small, implying that the collagen distribution was more compact. In chronological aging stages, the collagen orientation index and the collagen bundle packing were bigger. It was indicated that the collagen alignment was more parallel with ages. While for photoaging skin, the collagens were destroyed seriously by UV light. So the collagen orientation index was small, but the collagen bundle packing was larger. It revealed that the mechanism varies with different types of aging in collagen texture.3. The optical parameters of collagen were taken as new effective marks for evaluation different types aging skin. We used optical coherence tomography to monitor the process of chronological aging and photoaging skin. Then, the attenuation coefficient in different skin layers and epidermis thickness were extracted in vivo based on the OCT signal scattering model. The results display that the attenuation coefficient in dermis decrease with ages and environment effect, such as UV irradiation.4. Based on the results of above, in experimental study in vivo, the opto-thermal response of the different laser source including ablative laser and nonablative laser, such as Er:YAG laser, CO2 laser, Nd:YAG laser, and Intense Pulsed Light source were irradiated on different types skin in order to discuss the mechanism of laser ablative and non ablative rejuvenation. Then, the changes of collagen morphology during the process of renovation were obtained and the changes of optical parameter, morphology and texture feature in collagen were extracted. The results could quantitative show the relation between laser-tissue effect and collagen synthesis and reveal the mechanism of rejuvenation from sub-micro magnitude to millimeter magnitude. The key point of rejuvenation was proposed. The therapeutic effects of different laser sources were found:the Intense Pulsed Light source and Nd:YAG laser could only used to improve the fine wrinkle, but it had no effect to cure the photoaging skin; the Er:YAG laser, CO2 laser had good results to treatment the photoaging skin, but had many complications. Moreover, the study established a basis for further understanding of clinical study in the rejuvenation.