Lindmo T, Smithies D J, Chen Z, Nelson J S, Milner T E
Department of Physics, Norwegian University of Science and Technology, Trondheim.
Phys Med Biol. 1998 Oct;43(10):3045-64. doi: 10.1088/0031-9155/43/10/025.
A Monte Carlo model has been developed for optical Doppler tomography (ODT) within the framework of a model for optical coherence tomography (OCT). A phantom situation represented by blood flowing in a horizontal 100 microm diameter vessel placed at 250 microm axial depth in 2% intralipid solution was implemented for the Monte Carlo simulation, and a similar configuration used for experimental ODT measurements in the laboratory. Simulated depth profiles through the centre of the vessel of average Doppler frequency demonstrated an accuracy of 3-4% deviation in frequency values and position localization of flow borders, compared with true values. Stochastic Doppler frequency noise was experimentally observed as a shadowing in regions underneath the vessel and also seen in simulated Doppler frequency depth profiles. By Monte Carlo simulation, this Doppler noise was shown to represent a nearly constant level over an investigated 100 microm interval of depth underneath the vessel. The noise level was essentially independent of the numerical aperture of the detector and angle between the flow velocity and the direction of observation, as long as this angle was larger than 60 degrees. Since this angle determines the magnitude of the Doppler frequency for backscattering from the flow region, this means that the signal-to-noise ratio between Doppler signal from the flow region to Doppler noise from regions underneath the flow is improved by decreasing the angle between the flow direction and direction of observation. Doppler noise values from Monte Carlo simulations were compared with values from statistical analysis.
在光学相干断层扫描（OCT）模型的框架内，已经开发出一种用于光学多普勒断层扫描（ODT）的蒙特卡罗模型。在蒙特卡罗模拟中，实现了一种虚拟情况，即血液在水平放置的直径为100微米的血管中流动，该血管位于2%脂质乳剂溶液中轴向深度为250微米处，并且在实验室中用于ODT实验测量的配置与之类似。通过血管中心的平均多普勒频率的模拟深度剖面表明，与真实值相比，频率值和流动边界的位置定位偏差的准确度为3%-4%。实验观察到随机多普勒频率噪声在血管下方区域表现为阴影，并且在模拟的多普勒频率深度剖面中也能看到。通过蒙特卡罗模拟，这种多普勒噪声在血管下方100微米的研究深度间隔内显示为接近恒定的水平。只要该角度大于60度，噪声水平基本上与探测器的数值孔径以及流速与观察方向之间的角度无关。由于该角度决定了来自流动区域的后向散射的多普勒频率大小，这意味着通过减小流动方向与观察方向之间的角度，可以提高来自流动区域的多普勒信号与来自流动下方区域的多普勒噪声之间的信噪比。将蒙特卡罗模拟得到的多普勒噪声值与统计分析得到的值进行了比较。
