Evans D H
Ultrasound Med Biol. 1985 Sep-Oct;11(5):735-41. doi: 10.1016/0301-5629(85)90107-3.
A number of modern duplex scanners now have facilities for determining volumetric blood flow through intact vessels. The methods these machines use to arrive at an answer must presuppose a number of conditions which may not be met in practice. This paper examines the effect that nonuniform insonation of the target blood vessel (using continuous wave or wide-gate pulsed ultrasound) has on the mean velocity, as determined using mean, root mean square (RMS) and maximum frequency processors. It is shown that for a given beam/vessel geometry the error is dependent only on the shape of the mean component of the velocity profile which, depending on the arterial site, may be flat, parabolic or intermediate. Mean processors may overestimate the mean velocity of established flow by up to 33%, but this could be turned to advantage when it is impracticable to insonate a vessel uniformly. Maximum frequency processors are of value when either plug-flow or fully established flow of low pulsatility is present in the target vessel. In the first case the mean flow is the same as the maximum flow, while in the second the mean flow is half the time averaged maximum flow, irrespective of the size and shape of the ultrasound beam. RMS processors are probably best avoided in volumetric flow measurement applications.
现在有许多现代双功扫描仪具备测定完整血管内体积血流量的功能。这些机器用于得出结果的方法必定预先假定了一些在实际中可能无法满足的条件。本文研究了（使用连续波或宽门脉冲超声）对目标血管进行非均匀声照射时，采用平均、均方根（RMS）和最大频率处理器测定的平均速度所产生的影响。结果表明，对于给定的波束/血管几何形状，误差仅取决于速度剖面平均分量的形状，根据动脉部位的不同，该形状可能是平坦的、抛物线形的或中间形的。平均处理器可能会将已建立血流的平均速度高估多达33%，但当对血管进行均匀声照射不切实际时，这一点可能会转化为优势。当目标血管中存在塞流或低搏动性的充分建立的血流时，最大频率处理器很有价值。在第一种情况下，平均血流与最大血流相同，而在第二种情况下，平均血流是时间平均最大血流的一半，与超声束的大小和形状无关。在体积血流测量应用中，可能最好避免使用RMS处理器。
