• colour Doppler
• cardiac output
• digital
• ultrasound
• haemodynamics

In the 1980s, the development of Doppler echocardiography, especially pulsed wave Doppler techniques, provided significant progress in determining cardiac flow volumes.^1–3 The pulsed wave Doppler method is based on a simple mathematical principle, which multiplies a flow area by its velocity during the flow time (velocity–time integral) to estimate a flow volume.^1–3 This Doppler method assumes a spatially flat flow velocity distribution and a constant flow area during the entire time of flow. However, the spatial velocity profile is not necessarily flat and the flow area may change during the time of flow.^1–3

In the 1990s, a digitally automated cardiac flow measurement method was developed to overcome these shortcomings of the conventional pulsed Doppler method.^4–11 This new method uses not only a single central point but also multiple Doppler points in space along the diameter of the flow; it also uses several imaging frames during the time of flow, accounting for the temporal change in the flow area (that is, not assuming a constant flow area).⁴ In addition, the calculation does not require manual tracing of the Doppler velocity nor the measurement of flow diameter. Thus, the actual use of this automated method in clinical settings is simpler and easier than the conventional pulsed Doppler method.^6–11