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Self-gating (SG) is a cardiac MRI technique to synchronize data acquisition to the cardiac cycle based upon MR signal triggers as opposed to conventional ECG triggers. Fourteen healthy subjects underwent cardiac MRI scans in four different orientations: two chamber, three chamber, four chamber, and short axis. SG trigger times were computed using two methods, first difference and template matching, and ECG trigger times were also recorded for comparison. The root-mean-square (RMS) error was used to evaluate performance, defined as the variability relative to the mean difference between SG trigger times and ECG trigger times. The mean RMS error was lower for template matching than first difference approach for all scan orientations; the improvement in RMS error was statistically significant for all orientations except short axis. In conclusion, compared to the first difference approach, template matching improved the accuracy of trigger detection for two, three, and four chamber SG cardiac MRI scans.

The magnetohydrodynamic (MHD) effect generates voltages which distort the ECG obtained during cardiac MRI. Consequently, MHD voltages result in triggering problems for MR image acquisition. In addition, since the MHD effect is related to blood flow, analysis of it not only as interference, but also as a signal may provide useful blood flow information. Comsol Multiphysics modeling software was used to compute and model the MHD voltages in 3D. These voltages were compared with MHD voltages obtained experimentally from the subtraction of ECGs taken outside the MRI magnet from ECGs taken inside the magnet. The maximum MHD voltage magnitude for the experimental data was 0.2 mV and was 3.04 mV for the modeled data when calculated on the surface of the uniform volume conductor. By modeling MHD voltages in 3D, we can learn about their effect on the ECG during cardiac MRI.

Pacemaker outputs are poorly recorded and displayed by the standard ECG. A new high resolution ECG system optimized for recording outputs from electronic pacemakers was evaluated. Three ECGs with different pulse settings were recorded in 42 patients with pacemakers at a sampling rate of 75 kHz using a new ECG acquisition module. Atrial and ventricular pulses were detected and the measured pulse widths and amplitudes were compared to the programmed values. For the atrium, the correlations between programmed and measured width and amplitude were 0.85 and 0.74, while for the ventricle they were 0.99 and 0.8. Leads II and V1 had the highest atrial amplitude, and leads V3, V4 and V5 had the highest ventricular amplitude. The new high resolution ECG pacemaker system dramatically improved the reproduction of pacemaker outputs, allowing accurate measurement of pulse duration for both atrial and ventricular pulses.