Nguyen Linh Chi, Yu François T H, Cloutier Guy
Laboratory of Biorheology and Medical Ultrasonics, Centre hospitalier de l'Université de Montréal (CHUM)-Hôpital Notre-Dame, Montréal, Québec, Canada.
Ultrasound Med Biol. 2008 Apr;34(4):664-73. doi: 10.1016/j.ultrasmedbio.2007.10.002. Epub 2008 Jan 9.
Previous in vivo and in vitro studies have demonstrated that blood echogenicity varies under pulsatile flow, but such changes could not always be measured at physiological stroke rates. The apparent contradiction between these studies could be a result of the use of different ultrasound frequencies. Backscattered signals from porcine blood were measured in a pulsatile Couette flow apparatus. Cyclic changes in shear rate for stroke rates of 20 to 70 beats per minute (BPM) were applied to the Couette system, and different blood samples were analyzed (normal blood and blood with hyperaggregating erythrocytes promoted with dextran). To confirm that cyclic echogenicity variations were observable, spectral analysis was performed to verify if changes in echo-amplitude corresponded to the stroke rate applied to the flow. Echogenicity was measured with two single-element transducers at 10 and 35 MHz. At 35 MHz, cyclic variations in backscatter were observed from 20 to 70 BPM. However at 10 MHz, they were detected only at 20 BPM. For all cases except for hyperaggregating red blood cells (RBCs) at 20 BPM, the magnitude of the cyclic variations were higher at 35 MHz. We conclude that cyclic variations in RBC aggregation exist at physiological stroke rates, unlike what has been demonstrated in previous in-vitro studies at frequencies of 10 MHz. The increased sensitivity at 35 MHz to small changes in aggregate size might be the explanation for the better characterization of RBC aggregation at high stroke rates. Our results corroborate in-vivo observations of cyclic blood echogenicity variations in patients using a 30-MHz intravascular ultrasound catheter.
先前的体内和体外研究表明，在脉动血流情况下血液的回声性会发生变化，但在生理搏率下，这种变化并非总能被测量到。这些研究之间明显的矛盾可能是由于使用了不同的超声频率。在脉动库埃特流装置中测量了猪血液的背向散射信号。将每分钟20至70次搏动（BPM）的搏率下的剪切率循环变化应用于库埃特系统，并对不同的血液样本（正常血液和用右旋糖酐促进红细胞过度聚集的血液）进行了分析。为了确认是否可观察到回声性的循环变化，进行了频谱分析，以验证回声幅度的变化是否与施加于血流的搏率相对应。使用两个10 MHz和35 MHz的单元素换能器测量回声性。在35 MHz时，观察到20至70 BPM之间背向散射的循环变化。然而，在10 MHz时，仅在20 BPM时检测到这种变化。对于除20 BPM时的过度聚集红细胞（RBC）外的所有情况，35 MHz时循环变化的幅度更高。我们得出结论，与先前在10 MHz频率下的体外研究结果不同，在生理搏率下存在RBC聚集的循环变化。35 MHz对聚集大小微小变化的敏感性增加可能是在高搏率下更好地表征RBC聚集的原因。我们的结果证实了使用30 MHz血管内超声导管对患者进行的循环血液回声性变化的体内观察。
