[Reliability of duplex sonography in non-quantitative determination of blood flow in comparison to inductive flow...

Using an experimental design permitting generation of a pulsatile "flow-velocity waveform" corresponding to the fetal aortic signal, the influence of measurement depth, the angle between the Doppler beam and the vessel, the high-pass filter and the extent of overlap between the "sample volume" and the vessel cross-section were studied in vitro. The Resistance Index showed the best relation to inductive flow measurement, which was defined as standard. Considering the conditions prevailing during clinical studies, good reliability is likely at angles of between 0 degrees and 60 degrees (120 degrees-180 degrees) over the entire range of measuring depths (4-13 cm) and when using 100-200 Hz high-pass filters. The magnitude and location of the sample volume does not seem to play a decisive role provided a part of it is within the sonographically imaged "vessel" and there is no likelihood of interference from vessels in the immediate vicinity in which blood flow is in the same direction.