Department of Electrical Engineering, Fu Jen Catholic University, Taipei, Taiwan.
IEEE Trans Ultrason Ferroelectr Freq Control. 2011 Feb;58(2):357-68. doi: 10.1109/TUFFC.2011.1813.
Ultrasonic backscatter has recently been used extensively to investigate erythrocyte aggregation, which is an inherent hematological phenomenon in the blood circulation system. The size of rouleaux can be estimated by measuring certain parameters of signals backscattered from flowing blood. However, most measurements of backscatter from blood use a constant value for the attenuation coefficient to compensate for the loss of ultrasound energy. This correction may be inaccurate because the attenuation varies with the blood properties, which prompted us to explore the effects of hemodynamic properties on ultrasonic attenuation and backscatter to better understand the blood rheological behaviors. Experiments were performed on porcine whole blood in a Couette flow apparatus. Ultrasonic attenuation and the backscattering coefficient of blood were measured at various frequencies (from 10 to 50 MHz), hematocrits (from 0 to 60%), and shear rates (from 0.1 to 200 s⁻¹). The results indicated that the attenuation and backscattering coefficients of blood are highly variable, depending in a complex manner on shear rate, hematocrit, and the measurement ultrasound frequency. The attenuation of blood decreased rapidly with increasing shear rates, eventually reaching a steady state asymptotically, and increased linearly with the hematocrit from 10 to 50 MHz at various shear rates, and also with the ultrasound frequency. The effect of erythrocyte aggregation means that the change in ultrasonic attenuation in blood with shear rate may be attributed to the absorption mechanism, which is enhanced by the increased blood viscosity at lower shear rates. Compensating the measured backscattering coefficients of blood for the shear-rate-dependent attenuation coefficient increased the accuracy of erythrocyte aggregation assessments. Together, the experimental results suggest that the shear-rate-dependent attenuation coefficient should be considered in future developments of ultrasonic technologies for characterizing blood rheology when the ultrasound frequency is higher than 20 MHz.
超声背向散射最近被广泛用于研究红细胞聚集，这是血液循环系统中的固有血液现象。通过测量从流动血液中背向散射的信号的某些参数，可以估计血饼的大小。然而，大多数血液背向散射的测量都使用衰减系数的恒定值来补偿超声能量的损失。这种校正可能不准确，因为衰减随血液特性而变化，这促使我们探索血液的流变性对超声衰减和背向散射的影响，以更好地了解血液的流变性行为。实验是在 Couette 流动装置中对猪全血进行的。在各种频率（10 至 50MHz）、红细胞压积（0 至 60%）和剪切率（0.1 至 200s⁻¹）下测量了血液的超声衰减和背散射系数。结果表明，血液的衰减和背散射系数高度可变，复杂地取决于剪切率、红细胞压积和测量超声频率。血液的衰减随剪切率的增加而迅速下降，最终达到渐近稳定状态，并且在各种剪切率下，红细胞压积从 10MHz 线性增加到 50MHz，并且与超声频率呈线性关系。红细胞聚集的影响意味着，血液中超声衰减随剪切率的变化可能归因于吸收机制，在较低的剪切率下，血液粘度的增加增强了该机制。补偿血液的测量背散射系数与剪切率相关的衰减系数提高了红细胞聚集评估的准确性。总的来说，实验结果表明，当超声频率高于 20MHz 时，在未来开发用于表征血液流变性的超声技术时，应该考虑剪切率相关的衰减系数。
