Study of absorption and scattering properties of tissues

为了研究血液的散射特性，研制了一种光学测量系统。测量了稀释后血液的散射图，并与米氏理论进行了比较，估计了光学参数。实验方法如下：采用直径为9mm的圆柱形石英管作为样品池。将细胞置于水浴中，由激光二极管发出的偏振和准直激光束通过光学窗口照射。样品的散射光由测角仪臂上固定的光纤收集，检测到的光通过雪崩光电二极管转换成电信号。激光束波长为805 nm。以已知光学参数的球形丙烯酸颗粒悬浮液为参考。球的折射率为1.49。采用直径分别为1.5和5.0的两种球型。利用Mie理论计算了各参考样品的微分散射截面散射（单位体积和单位入射光强的散射功率）。将测量到的散射功率（0.00245%）除以理论计算得到的微分散射截面，确定仪器系数。新鲜人血用生理盐水稀释以保持单散射状态。对血液样本（红细胞比容0.025%、0.011%、0.0058%、0.0028%）散射光进行角质层光测量，然后利用仪器因子将测量结果解释为血液的微分散射截面。从测量中可以看出，稀释后的血液各向异性参数约为0.99，单次散射状态下红细胞每1%体积分数的散射系数约为7 （mm^<-1>）。

To investigate the scattering properties of blood, goniophotometric measurement system was developed. The scattering diagram of diluted blood was measured and compared the results with the Mie theory, and estimated the optical parameters.The experimental method is as follows. A cylindrical quarts tube of 9mm in diameter was used as a sample cell. The cell was set in a water bath, and illuminated through an optical window by polarized and collimated laser beam from a laser diode.The scattered light from the sample was collected by an optical fiber hold by the arm of the goniometer, and detected light was transformed to electric signal by an abalanche photodiode. The wavelength of laser beam was 805 nm.Suspensions of spherical acrylic particles with known optical parameters were used as the reference. The Refractive index of sphere was 1.49. Two type of spheres with 1.5 and 5.0 in diameter were used. The differential scattering cross section scattering (scattered power per unit volume per unit incident light intensity) were theoretically calculated for the each reference sample by using Mie theory.By dividing the measured scattered power from the reference sample (0.00245%) by the differential scattering cross section obtained from the theoretical calculation, the instrument factor was determined.Fresh human blood were diluted with a physiological saline to hold single scattering status. Goniophotometric measurements of scattered light from blood samples (Hematocrit 0.025%, 0.011%, 0.0058%, 0.0028%) were carried out, and then those measured results were interpreted to the differential scattering cross sections of blood by using the instrument factor.From the measurement, it ca be seen that anisotropic parameter of diluted blood is around 0.99, and Scattering coefficient per 1% volume fraction of red blood cells in single scattering status is about 7 (mm^<-1>).