Ren T, Nuttall A L, Miller J M
Kresge Hearing Research Institute, University of Michigan Medical School, Ann Arbor 48109-0506, USA.
Microvasc Res. 1995 Mar;49(2):233-45. doi: 10.1006/mvre.1995.1019.
A system has been developed for the measurement of relative blood velocity in micro-vessels by using the self-mixing effect of a laser. A helium-neon laser was coupled to a single-mode optical fiber and the pulled fiber tip (approximately 30 microns diameter) was positioned on a single microvessel. The backscattered Doppler-shifted laser light from moving red blood cells enters the laser cavity and modulates the laser output by influencing internal laser parameters. The signal of the laser output intensity change was produced using a fiber-coupled photodiode and processed by a signal processor. This processor yields an output signal proportional to the first moment of the power spectral density, i.e., the mean frequency of the Doppler shift, corresponding to the blood flow velocity on an arbitrary instrument scale. Results of the in vitro experiment demonstrated that the current method can detect moving particles in fluid and moving red blood cells in a small plastic tube. Data from the in vivo study showed that this system is capable of measuring relative blood velocity in arterioles and venules and can easily follow the cardiac cycle up to 360 beats/min. Primary data suggest that, in addition to high sensitivity, good spatial and temporal resolution, and convenience of use, the self-mixing technique may have an even greater capacity for analysis of blood flow in microvessels than explored in this study, since information on the absolute velocity and velocity distribution of red blood cells is available in self-mixing signal. Further study on its hematocrit dependence and particle bias effect is needed.
已经开发出一种利用激光的自混合效应来测量微血管中相对血流速度的系统。将氦氖激光器耦合到单模光纤上，并将拉细的光纤尖端（直径约30微米）放置在一根微血管上。来自移动红细胞的后向散射多普勒频移激光进入激光腔，并通过影响内部激光参数来调制激光输出。激光输出强度变化的信号由光纤耦合光电二极管产生，并由信号处理器进行处理。该处理器产生一个与功率谱密度的一阶矩成正比的输出信号，即多普勒频移的平均频率，对应于任意仪器刻度上的血流速度。体外实验结果表明，当前方法能够检测流体中的移动颗粒以及小塑料管中的移动红细胞。体内研究数据表明，该系统能够测量小动脉和小静脉中的相对血流速度，并且能够轻松跟踪高达360次/分钟的心动周期。初步数据表明，除了具有高灵敏度、良好的空间和时间分辨率以及使用便利性之外，自混合技术在分析微血管中的血流方面可能具有比本研究中所探索的更大的能力，因为自混合信号中包含红细胞的绝对速度和速度分布信息。需要对其对血细胞比容的依赖性和颗粒偏差效应进行进一步研究。
