生物组织多光谱偏振特性研究

Study on Multispectral Polarization Characteristics of Biological Tissues

生物组织内部结构复杂且具有较强的散射特性,而光作为生物组织检测的重要信息载体,其自身特性包括颜色、幅值、偏振等都对信息获取有较大的影响。结合偏振成像,对生物组织多光谱偏振特性展开了研究,依据不同微粒尺寸的分布建立了均匀单层生物组织模型,结合瑞利和米氏散射理论模拟了基于单个微粒的两种散射事件。瑞利散射具有较好的前向后向散射对称性,米氏散射具有强前向散射特性,两种散射模型都与尺寸参数有着密切的关系,而尺寸参数是一个无因次量,取决于入射波长和散射微粒的尺寸,在生物组织中多以米氏散射为研究模型。使用蒙特卡罗(Monte Carlo MC)方法对400~1000 nm波段范围内的偏振光在生物组织中的传输特性进行了仿真,模拟了四种典型偏振态(水平线偏振光、垂直线偏振光、45°线偏振光和右旋圆偏振光)在组织中传播时后向散射光偏振态变化与波长的关系,并进行了实验验证,实验光源选用白色LED灯,利用450,525,550,590,610,650和690 nm滤光片滤光,由彩色相机记录手掌的偏振图像,其中偏振图像由两组线偏振片和右旋圆偏振片分别作为起偏和检偏器产生。仿真和实验结果均表明,随着波长增加线偏振光经皮肤组织后向散射出射光的偏振度整体呈上升趋势,圆偏振光呈下降趋势,但圆偏振光的偏振度整体上高于线偏振光,这揭示了在生物组织中相同波长的圆偏振光比线偏振光具有更好的偏振保持性,更适合用于探测生物组织的生理信息。相关研究结果明确了圆偏振光和线偏振光在生物组织中传输时的多光谱特性,可为多光谱偏振生理信息获取提供一定的理论支持。

Biological tissues are very complicated with strong scattering characteristics.The light-source of detecting physiological parameters of tissues is critical.Combined with the advantages of polarization imaging,this paper studies the multispectral polarization characteristics of biological tissues.We established uniform monolayer biological tissue samples based on the distribution of different particle sizes and simulated the scattering model with single-particle by combining Rayleigh and Mie scattering theory.Rayleigh theory has good forward and backward scattering symmetry;Mie theory has strong forward scattering characteristics.The two scattering models are closely related to the size parameter,a dimensionless quantity,depending on the incident wavelength and the size of scattered particles.Mie theory is generally used as the research model in biological tissues.We used a Monte Carlo method to simulate the transmission characteristics of polarized light in the tissue model.The wavelength range is 400~1000 nm.In this paper,we have simulated four typical polarization states,(horizontally polarized light,vertically polarized light,450 linearly polarized light and right-rotated circularly polarized light).The experiment system used a white LED lamp as a light source.It used filters to obtain different wavelength beams,a color camera was used to record the image of the target,two groups of linear polarizers and right-rotated circular polarizers were used as polarizers and analyzers to test horizontally polarized light,and right-rotated circular polarized light with wavelengths of 450,525,550,590,610,650 and 690 nm,respectively,and the target is our palm.Both simulation and experimental results show that with the increase of wavelength,the degree of polarization(DOP)of linearly polarized light after backscattering from skin tissue shows an overall upward trend,while that of circularly polarized light is on the decline.However,the overall DOP of circularly polarized light is higher than that of linearly polarized light,which indicates that circularly polarized light has better polarization retention than linearly polarized light in biological tissues and is more suitable for detecting physiological information.Our study has confirmed the multispectral characteristics of circularly polarized light and linearly polarized light transmitted in tissues,which provided theoretical support for obtaining multispectral polarization physiological parameters.