应用光谱方法测量生物组织成分时, 信号的拾取一般有两种方法: 透射法和反射法。 其中, 根据光纤测头与生物组织接触与否, 反射法分为接触和非接触两种形式。 接触测量时, 只有携带了组织信息的深层反射光进入测头, 但接触测量中压力、 温度等变化会导致测量条件的变化, 进而影响光谱数据的稳定性; 非接触测量时, 虽然克服了接触压力、 测头温度等对测量的干扰, 却会导致不携带光与组织相互作用信息的表面反射光进入测头, 由于表面反射光强度高且集中, 将会影响检测器的动态范围。 因此非接触测量的最大问题是如何有效地消除生物组织表面反射光的影响。 针对非接触测量中生物组织表面反射光的消除方法进行了系统研究, 对课题组之前提出的正交偏振法进行了理论和实验分析。 首先, 以不同被测物为对象, 研究了表面反射光的偏振态, 结果表明表面反射光的偏振度与表面粗糙度密切相关, 表面粗糙程度越小, 偏振度越高, 由此推断出, 经表面光滑的Intralipid溶液反射后的表面反射光具有保偏特性; 然后, 以Intralipid-20%溶液为被测对象, 对正交偏振法消除表面反射光的效果进行了研究, 实验结果显示正交偏振法可以消除97%以上的表面反射光; 最后, 比较分析单波长下不同源探距离处的接触和非接触式光谱测量曲线, 二者高度重合, 这一现象进一步说明了正交偏振法消除表面反射光的有效性。 该研究通过评价正交偏振法消除组织表面反射光的能力, 旨在消除接触式漫反射光谱检测中测量条件变化对测量的影响, 以期推动近红外无创光谱检测技术的进一步发展。

In the analysis of the body component with spectroscopic techniques, transmission method and reflection method are two common approaches that used for the signal acquisition. Based on the position relationship between the optical fiber probe and the biological tissue, the reflection method can be further divided into two forms: contact measurement and non-contact measurement. The traditional contact measurement can easily realize the extraction of useful signals from deep tissue by adjusting the position between the light source and receiving fiber. However, study shows that the contact pressure and the heat transfer between the probe and tissue are known to cause the change of measurement conditions, which will further influence the stability of spectral data. By comparison, non-contact method is free from the influence of changes of pressure and temperature. Nonetheless, large amounts of surface reflectance that do not carry any useful information will be gathered into the fiber. The surface reflectance is so strong and concentrated that it would easily influence the dynamic range of the detector. Therefore, how to eliminate the impact of surface reflectance is the biggest problem the non-contact measurement faces. In view of this, a systemic study is conducted in this article and the cross- polarization method proposed by our group is investigated through both theoretical deduction and experimental analysis. First, the polarization state of surface reflection with different objects as experimental materials is studied. Results indicate that the polarization state of the surface reflectance is closely related to the surface roughness, the smaller the roughness is, the higher the polarization state will be. As a result, it can be concluded that the surface reflectance of Intralipid solution possesses with the polarization-maintaining property. Then, the extinction effect of the cross-polarization method was verified in Intralipid-20% solutions. Results showed that 97 percent of the surface reflections were eliminated effectively through this method. Finally, a comparative analysis on spectral data respectively obtained by contact and non-contact measurement was carried out. Result showed that there was a high coincidence between the two curves, which further illustrated the cross-polarization method can effectively eliminate the surface reflectance. Overall, this research explored the ability of cross-polarization method to eliminate the surface reflectance, aiming at abolishing the effect caused by the variations of measurement conditions and further promoting the development of non-invasive sensing with NIR spectroscopy technique.