Determining the influence of age and diabetes on the second-harmonic generation strength of dermal collagen fibers in vivo by using electronic noises

摘要

It is commonly believed that intrinsic skin aging is associated with the change of the collagen structures. The influence of the diabetes on the skin collagen is also considered to be similar to aging. Moreover, second-harmonic-generation (SHG) in collagen fibers is known to reflect the detailed collagen structures. It is thus highly valuable to adopt the SHG intensity as a collagen structure indicator. With the help of SHG, recently one can achieve in vivo imaging which provides the information of what really happens beneath the human skin. However, when analyzing the images, the SHG brightness of each pixel highly depends on the illumination condition, the depth of the SHG source, and the voltage of PMT. Therefore, it is important to calibrate these factors before statistical analysis. In this paper, we present our recent development that calibrates the in vivo SHG images by using noises. We first determine the regions of signals and noises by setting a threshold relating to the standard deviation of the image. By using the assumption that the noise was amplified by PMT with an amplification ratio the same as the SHG signal, we can define the brightness of the noise region as a parameter representing the voltage of PMT, and use this parameter to calibrate all SHG images. After calibrating, we can then compare different images from volunteers and analyze the influence of aging and diabetes on the SHG intensity from collagen fibers, even if the voltage of PMT was not fixed.