Lupotti Fermín A, Zimmer Audrey, Daronat Michel, Foster F Stuart, van Der Steen Antonius F W, Cloutier Guy
Experimental Echocardiography, Thoraxcenter, Erasmus Medical Center, Rotterdam, The Netherlands.
Ultrasound Med Biol. 2004 Feb;30(2):205-14. doi: 10.1016/j.ultrasmedbio.2003.10.006.
Recent computer simulations suggest that the presence of aggregates of red blood cells (RBCs), at random angles and lengths, does not affect the measurements of blood flow transverse to the ultrasound (US) beam direction using a correlation-based method and an intravascular (IV) US array catheter. However, in case of aggregates of RBCs aligned with the flow, measurements of simulated blood velocity are affected. Blood velocity gradients were also shown not to influence the correlation-based method for blood velocity estimation. The objective of this study was to quantify the influence of aggregates of RBCs and blood velocity gradients on the correlation-based method during in vitro experiments. For this purpose, measurements were performed on washed RBCs (no aggregation), normal human blood, and two types of diseased blood in which a lower or a higher level of aggregation was present. The decorrelation pattern of a circular US transducer as a function of transverse blood flow was studied using a Couette system. Changing the shear rate of the Couette system modified the aggregation level of RBCs and the velocity gradient. With the exception of the results at low shear rates and abnormally high aggregation levels, agreements were found between the autoconvolution of the acoustical beam (reference curve) and the radiofrequency (RF) decorrelation patterns. For the high shear rate present in coronary arteries, the correlation-based method for blood flow estimation should not be influenced by these phenomena.
最近的计算机模拟表明，随机角度和长度的红细胞（RBC）聚集体的存在，不会影响使用基于相关性的方法和血管内（IV）超声阵列导管对垂直于超声（US）束方向的血流测量。然而，在红细胞聚集体与血流方向一致的情况下，模拟血流速度的测量会受到影响。血流速度梯度也显示不会影响基于相关性的血流速度估计方法。本研究的目的是在体外实验中量化红细胞聚集体和血流速度梯度对基于相关性方法的影响。为此，对洗涤后的红细胞（无聚集）、正常人血液以及存在较低或较高聚集水平的两种患病血液进行了测量。使用库埃特系统研究了圆形超声换能器的去相关模式作为横向血流的函数。改变库埃特系统的剪切速率会改变红细胞的聚集水平和速度梯度。除了低剪切速率和异常高聚集水平的结果外，在声束的自卷积（参考曲线）和射频（RF）去相关模式之间发现了一致性。对于冠状动脉中存在的高剪切速率，基于相关性的血流估计方法不应受这些现象的影响。
