Fig. 1

a Schematic view of the Doppler ultrasound (DUS) setup. The DUS transducer was placed over the heart on the subject’s chest. The exact location was adjusted while observing the signal on the DUS interface box to achieve a clear signal. The trigger signal from the DUS box was then converted to electrocardiogram (ECG) levels and connected to the ECG input device on the scanner. The cable between the transducer and DUS interface box included several radiofrequency (RF) traps to avoid heating of the cable. b Example of the timing of the triggers from the DUS diastolic wave (green, short dashes), DUS systolic wave (blue, long dashes) and ECG R-wave (red, dotted). As seen on the time scale, the triggers occur at different point in the cardiac cycle