基于偏振成像的面部皮肤结构和特征非接触在体测量方法

Non⁃Contact and In Vivo Polarization Imaging Method for Measuring Facial Skin Structures and Characteristics

数字成像技术能对皮肤的微观结构、生理特征、新陈代谢情况等进行描述,有助于对皮肤形态和动态平衡机制进行定量评估,对皮肤病筛查等具有重要意义。偏振成像方法以其非接触、信息量丰富、无需染色标记等特点,被广泛应用于包括皮肤检测在内的生物医学研究领域。本文提出了一种基于偏振成像的面部皮肤结构和特征的非接触在体测量方法,并利用这一方法分析了不同偏振成像模式对面部皮肤不同参数测量结果的影响。具体而言,首先构建了一套可调偏振成像模态的人体面部皮肤测量系统,然后分别在无偏振、平行偏振和正交偏振三种成像模式下对5个基于CIE Lab色彩空间和Frangi滤波器的面部皮肤参数进行了测量分析。通过对不同参数在面部不同区域的异质分布进行细化探究,得到了不同偏振模态成像获取特定面部皮肤参数的效果差异,并给出了不同参数的偏振测量建议,为提高临床应用中偏振成像非接触、定量测量皮肤参数的有效性奠定了基础。

Objective The physical structure,physiological characteristics,and health status of skin tissues are closely related to the quality of daily life and safety of the human body.Measuring human facial skin structures and characteristics has attracted increasing attention recently,because it can reveal the health conditions of the body and the dense distribution and complex structures of skin tissues in different regions.Polarization imaging is a noncontact labelfree method that can provide abundant optical and structural information of tissues.Thus,it has been applied on many biomedical studies including facial skin tissue detection.However,there is still a lack of systematic and quantitative studies on the skin tissue characterization of different facial regions using polarization imaging parameters,which hinders further dermatological applications of polarimetry.To deal with this problem,we proposed a noncontact and in vivo measurement method of facial skin structures and characteristics based on polarization imaging;this method can obtain the heterogeneous distribution of five skin parameters in different facial regions under three polarization modes.Our results suggested ways of improving the effectiveness of noncontact and quantitative measurements of appropriate facial skin parameters by polarization imaging in future dermatological applications.Methods For human facial skin imaging,we first developed a polarizationadjustable instrument that is mainly composed of a light source,the linear polarization modulators,and a camera.It can extract the information of the skin surface and deep skin layer by using three polarization imaging modes,namely,nonpolarized imaging(NPI),parallelpolarized imaging(PPI),and crosspolarized imaging(CPI).We recruited 15 healthy male(age 30.4±7.7 years old)and 5 female(age 29.4±7.4 years old)volunteers,respectively,their front,left,and right facial regions were imaged under the three polarization modes introduced above.The L*,b*,a*,and individual typological angle(ITA)parameters based on the CIE Lab color space,which are often used to assist dermatological studies,and the t parameter of the skin texture feature extracted by the Frangi filter were selected to further analyze the measurement results of distinct facial regions(cheek,upper eyelid,forehead,nose,and perioral area).The skin structures and characteristics of different facial anatomical regions of the volunteers were evaluated by dermatologists of the China Academy of Chinese Medical Sciences as the analysis criteria in this study.Results and Discussions The results indicated that there are significant differences in the measurement results of five parameters for the subjects’whole facial skin under different polarization imaging modes(P<0.01)(Table 1).Different polarization imaging modes and facial anatomical regions have significant differences in the measurement results of five parameters(P<0.01).The results suggested that the polarization imaging mode should be carefully selected to obtain accurate facial structure and feature parameters in followup researches.Regarding the characteristic parameters of facial skin,both the L*and ITA are related to skin pigmentation,which can hardly be evaluated by polarization imaging modes(Fig.3 and Fig.6).The parameters a*and b*focus on analyzing the degree of deposition information of chromophores in the deeper skin layers,which can be successfully evaluated by the CPI mode(Figs.4 and 5).Specifically,among the selected facial regions,the cheek region has the lowest combined concentration of chromophores in the epidermis and dermis,showing the lightest skin tone.Similarly,the forehead region is the most hyperpigmented.For the parameters of skin texture,the t parameter is related to skin aging and hydration.Compared with the NPI mode,the PPI mode can better reflect the length,width,and depth of skin stratum corneum wrinkles and hair shaft information,while the t parameter in the CPI mode can provide hair shaft texture information(Fig.7).Conclusions In this study,we proposed a noncontact and in vivo measurement method of human facial skin structures and characteristics based on polarization imaging.The influence of different polarization imaging modes on the measurement of five facial skin parameters is analyzed.Using this imaging system,we quantitatively explored the effect of three different polarization imaging modes,namely,NPI,PPI,and CPI,on the measurement of facial skin parameters of L*,a*,b*,ITA,and t.The results showed that for certain facial skin parameters,the selection of an appropriate polarization imaging mode for different facial anatomical regions can improve the measurement accuracy,better characterize the facial skin tissue structure,composition,and metabolism of the region of interest,and facilitate the evaluation of facial skin health conditions and detection of pathologies.Simultaneously,the results suggested that for the quantitative detection of other body skin areas,we still need to establish a clear relationship between the corresponding skin structure,composition,metabolism,and polarization imaging parameters.