Fig. 4.

Relationship between ECG, PO PPG and vPPG signals. Typical fiducial points of the ECG and their position relative to the cardiac cycle are shown. The systole lasts from the R-wave to the T-wave, followed by the diastole until the next R-wave. The PO PTT (pulse transmit time) is usually measured from the ECG R-wave to the beginning of the next PO rise. Triggers computed by the MRI-vendor-provided software on the basis of the PO signal are marked by black dots