生物组织单光程光谱技术的理论研究

高灵敏度光谱检测技术在临床诊疗和组织光学参数测量中具有极其重要的意义。文章提出了一种差分调制激光光谱技术，将经过生物组织后的散射光与参考光的光程差转换为光谱信号的频率特征，通过相敏检测技术将不同频率的信号进行分离，从而实现生物组织散射光的光程分离。文章分析了差分调制激光光谱的机理及信号的谱特征，并基于文献中的生物组织散射光的光程分布，从理论上讨论了差拍信号的谱特征，即光源调制速率一定时，光谱信号中的主频成分位置只与散射光和参考光的光程差有关；生物组织对光信号的衰减系数会影响光谱信号中频率成分的能量强度分布。分析结果表明，差分调制激光光谱能对生物组织的光谱信号进行光程分离，从而实现生物组织的单光程光谱检测。

Theoretical Analysis of the Single Optical Path Spectrum Detection in Biological Tissue

The technology of spectrum detection with high sensitivity is of significance in clinic diagnosis and tissue optical parameter measurement.A new method of difference-modulated laser spectrum detection was developed in the present paper.The measuring light and the reference light are separated from the lasing light source in this method.After passing through the tissue,the measuring light interferes with the reference light,and the frequency character of spectrum includes the information of the difference of optical path-length between the measuring light and reference light.By using the phase sensitive detector,the spectrum signal with different frequency can be separated,and consequently the measuring light passed through the tissue with different optical length will be apart.The mechanism of difference-modulated laser spectrum was analyzed and the value of dominant frequency of spectrum was deduced.Based on the theory of the optical path distribution in biological tissue,the spectrum signature of measuring light was discussed also.The distribution of dominant frequency component is decided by the difference of optical path-length between measuring light and reference light when the modulation parameters are invariable,and the magnitude of tissue's modulus decay will effect the energy distribution of spectrum frequencies component.Theoretical analysis showed that the method of difference modulation can be used to separate lights according to the optical path-length and realize the single optical path measurement in biological tissue.