Character of skin on photo-thermal response and its regeneration process using second-harmonic generation microscopy

Abstract

Quantitative characterization of skin collagen on photo-thermal response and its regeneration process is an important but difficult task. In this study, morphology and spectrum characteristics of collagen during photo-thermal response and its light-induced remodeling process were obtained by second-harmonic generation microscope in vivo. The texture feature of collagen orientation index and fractal dimension was extracted by image processing. The aim of this study is to detect the information hidden in skin texture during the process of photo-thermal response and its regeneration. The quantitative relations between injured collagen and texture feature were established for further analysis of the injured characteristics. Our results show that it is feasible to determine the main impacts of phototherapy on the skin. It is important to understand the process of collagen remodeling after photo-thermal injuries from texture feature.

Correlation between polarization sensitive optical coherence tomography and second harmonic generation microscopy in skin

“…Due to the thermal effect, the dermal birefringence decreased dramatically and the collagen structure became sparse and less organized. This is consistent with previous burn studies with PS-OCT [4][5][6][7] and SHG microscopy [16,17]. SHG intensity could be used to quantify the collagen content in the skin [16], but it was not applicable in this study: various sites of skin samples were compared and these skin samples had different thickness of the epidermis.…”

“…From the depth projection image, FFT was applied and the FFT power spectrum was plotted, then an ellipse curve fitting was applied to the power plot. The collagen orientation index I was calculated as I = 1 -S/L [17,22], where S and L were the lengths of minor and major axes of the fitted ellipse respectively. The value of I increases as the orientation of the structure increases.…”

“…Collagen has SHG property due to its non-centrosymmetric molecular structure [10]. SHG microscopy visualizes collagen fibers in the skin dermis and has been applied to various skin studies such as skin aging [11][12][13], skin cancer [14], Osteogenesis Imperfecta [15], and skin burn [16,17]. SHG microscopy has also been applied to in vivo human skin studies [11,13,18].…”

“…Multimodal approaches combining SHG microscopy with two-photon excited fluorescence, third harmonic generation and coherence anti-Stokes Raman scattering microscopy were developed [19]. For SHG image analysis, SHG intensity, organization, and complexity of collagen fiber distribution have been used as quantitative parameters [16,17,[20][21][22]. SHG intensity based analysis methods often suffer from thickness variation of the skin epidermis.…”

“…Collagen organization is important because it is related to mechanical properties and function of the skin [23,24]. Collagen organization was characterized by collagen orientation index which could be obtained from SHG images by either Fast Fourier Transform (FFT) or laser scattering method [17,22,25]. Recently, polarization sensitive SHG (PS-SHG) microscopy, which utilizes polarization sensitivity of SHG intensity from collagen fibers and other SHG source, has been developed to provide more detailed information [21,[26][27][28][29][30].…”