To the editor: Accurate measurement of cardiac output (CO) is important in clinical medicine. Current methods of calculation use two-dimensional echocardiography and ventricle volumetry or spectral Doppler pulse wave. Phase-encoded MRI is an accurate technique for volume assessment; however, is not suitable for many clinical situations, such as in those who are critically ill.

Previous work by our group has shown that real-time, three-dimensional Doppler echocardiography (RT3DDE) can accurately compute stroke volume (SV) and CO in an animal model against a “gold standard” of aortic flow probe using the left ventricular outflow tract colour Doppler signal,1 and this technique can be used in patients transthoracically.2 3

We tested the accuracy of RT3DDE of the left ventricular outflow tract for calculation of SV in a series of patients and healthy volunteers against a “gold standard” of phase-encoded MRI.

Two patients and 12 healthy volunteers took part in the study. The patients were undergoing MRI as part of their clinically indicated investigations for cardiac disease (both patients for aortic coarctation). All subjects gave written informed consent in accordance with the local Institutional Review Board.

The Philips Live 3D 7500 Sonos echocardiography system with a 3000-element 2–4 MHz xMATRIX transthoracic probe (Philips Medical Systems, Andover, Massachusetts, USA) was used for imaging. Subjects underwent echocardiography immediately before MRI.

Between three and five ECG-gated, three-dimensional colour Doppler volumes were acquired from …