应用超声微泡直接测量微小血管血流速度

Direct measurement of blood flow velocity in small diameter vessels by ultrasound microbubbles

目的应用超声微泡直接、非侵入性测量微小血管的血流速度。方法体外实验:用硅胶管建立一种模拟血流的体外模型,应用谐波超声追踪超声微泡在管内的流动,并录像。用"DFY型超声图像定量分析诊断仪"分析每帧中微泡的位置,以微泡的移动距离除以时间,得到微泡的移动速度。体内实验:建立9只大鼠直肠癌移植瘤模型,用与体外实验相同的方法测量大鼠直肠癌移植瘤内微小血管的血流速度。肿瘤切片HE染色,显微镜下测量肿瘤血管内径。结果体外实验:在体外模型中的血流标准速度分别为37.14 mm/s,21.01 mm/s和4.35 mm/s,应用本法测得的血流速度为(37.03±2.45)mm/s、(24.40±2.10)mm/s和(4.86±0.45)mm/s,两者间无统计学差异。体内实验:在肿瘤模型中所测得的小血管内血流速度为5.38～20.82 mm/s;HE染色发现9个肿瘤外周的最大血管内径平均为(142.76±24.03)μm,肿瘤内部的最大血管内径平均为(40.82±11.17)μm。这些小血管在常规多普勒超声下不能被探及。结论本实验测试了一种直接测量小血管的血流速度的新技术。结果表明,应用超声微泡可以准确测量小血管内的血流速度。经过对自动化跟踪技术的优化,这种新技术极有可能成为临床上非侵入性直接测量小血管血流速度的有效工具。

Objective To develop a direct, noninvasive ultrasound- guided method for measuring flow velocity in small vessels by ultrasound microbubbles. Methods In vitro, experiments were designed to mimick blood flow at different velocities inside tubes. Harmonic ultrasound imaging was used to track the movement of ultrasound microbubbles at a high frame rate. The movement of individual bubbles in the tubing was observed and recorded. The distance of the individual ultrasound signal traveled in successive frames was measured by DFY software and the mean flow velocity was calculated. In vivo, the flow velocity was measured in a subcutaneous tumor models in nine rats. A similar method was employed to calculate the blood flow velocity inside the tumor vessels. The internal diameter of the tumor vessels in each tumor was confirmed by hematoxylin and eosin （H＆E） stained tumor sections. Results In vitro, the blood flow velocities were found to be 37.14 mm/s, 21.01 mm/s and 4.35 mm/s, while the actual flow velocities were set at （37.03 ± 2.45）mm/s, （24.40 ±2.10）mm/s and （4.86 ± 0.45）mm/s, respectively. There were no significant differences between the actual and measured velocities. In vivo, the flow velocities in tumors were calculated to be 5.38 mm/s to 20.82 mm/s. The mean size for the largest vessels in the nine tumor capsules was （142.76 ± 24.03）tam and the mean size for the largest vessels inside the tumor was （40.82 ± 11.17）μm. This size was beyond the detection and measurement capability of the Doppler function on clinical ultrasound machine. Conclusion This study represents an initial attempt to demonstrate the feasibility of a new technique for blood velocity measurement in small diameter vessels. The results suggest that the technique can accurately determine the slow velocity in vessels. With proper development and automation, this approach may eventually become a valuable noninvasive tool in medical research and the clinic.