Jentink H W, de Mul F F, Hermsen R G, Graaff R, Greve J
Appl Opt. 1990 Jun 1;29(16):2371-81. doi: 10.1364/AO.29.002371.
Light propagation in a model for blood perfusion in tissue was simulated with Monte Carlo calculations to investigate the dependence of the output of laser Doppler perfusion meters on the configuration of the optical probe and on the multiple scattering of photons by moving particles in the tissue. Laser Doppler perfusion meters registrating the first moment ?v? and the first weighted moment ?v?(s) of the spectral power density S(v) of intensity fluctuations on a detector viewing tissue illuminated by a laser are considered. The model was scaled up about a factor of 10 compared with real tissue, to make experimental tests possible. From the simulations of the Doppler scattering, it will be shown that the location of the effective probe volume of the perfusion meter can be extended to deeper layers in tissue by increasing the distance between the illuminating light beam and the detector. This opens the possibility to measure perfusion in skin layers as a function of the distance to the surface. Other calculations show how the degree of multiple scattering of individual photons by moving cells determines which flow parameter is measured with the perfusion meter. If the degree is low, the output of the meter depends linearly on the mean velocity of cells. For high degrees, a dependence on the root mean square value of this distribution is found. At a high moving particle concentration, multiple scattering by moving particles also results in deviations from the linear dependence of ?v? on the concentration of moving particles and in deviations from the concentration independence of ?v?(s). Intensity distributions of light inside the tissue model were obtained from the simulations.
利用蒙特卡罗计算方法模拟了光在组织血液灌注模型中的传播，以研究激光多普勒血流仪的输出对光学探头配置以及组织中移动粒子对光子多次散射的依赖性。考虑了激光多普勒血流仪，它记录在观察激光照射组织的探测器上强度波动的光谱功率密度(S(v))的一阶矩(\langle v\rangle)和一阶加权矩(\langle v\rangle(s))。该模型比真实组织放大了约10倍，以便进行实验测试。从多普勒散射的模拟结果可以看出，通过增加照明光束与探测器之间的距离，血流仪有效探测体积的位置可以扩展到组织的更深层。这为测量皮肤层灌注随距表面距离的变化提供了可能性。其他计算结果表明，移动细胞对单个光子的多次散射程度决定了血流仪测量的是哪个血流参数。如果散射程度较低，血流仪的输出与细胞平均速度呈线性关系。对于高散射程度，发现其与该分布的均方根值有关。在移动粒子浓度较高时，移动粒子的多次散射还会导致(\langle v\rangle)对移动粒子浓度的线性依赖性以及(\langle v\rangle(s))对浓度独立性的偏差。通过模拟获得了组织模型内部的光强分布。
