7-Tesla Functional Cardiovascular MR Using Vectorcardiographic Triggering – overcoming the magnetohydrodynamic effect

Objective Ultra-high-field (B 0 ≥ 7 Tesla) cardiovascular magnetic resonance (CMR) offers increased resolution. However, ECG gating is impacted by the magneto-hydrodynamic (MHD) effect distorting the ECG trace. We explored the technical feasibility of a 7T MR scanner using ECG trigger learning algorithm to quantitatively assess cardiac volumes and vascular flow. Methods 7T scans performed on 10 healthy volunteers on a whole-body research MRI (Siemens Healthcare, Erlangen, Germany) with 8 channel Tx/32 channel Rx cardiac coil (MRI Tools GmbH, Berlin, Germany). Vectorcardiogram ECG was performed using a learning phase outside of the magnetic field, with a trigger algorithm overcoming severe ECG signal distortions. Vectorcardiograms were quantitatively analyzed for false negative and false positive events. Cine CMR was performed after 3 rd -order B 0 shimming using a high-resolution breath-held ECG-retro-gated segmented spoiled gradient echo, and 2D phase contrast flow imaging. Artefacts were assessed using a semi-quantitative scale. Results 7T CMR scans were acquired in all patients (100%) using the VCG learning method. 3,142 R-waves were quantitatively analyzed, yielding sensitivity 97.6%, specificity 98.7%. Mean image quality score was 0.9, sufficient to quantitate both cardiac volumes, ejection fraction (EF), aortic and pulmonary blood flow. Mean LVEF was 56.4%, RVEF 51.4%. Conclusion Reliable cardiac ECG triggering is feasible in healthy volunteers at 7T utilizing a state-of-the-art 3-lead trigger device despite signal distortion from the MHD effect. This provides sufficient image quality for quantitative analysis. Other ultra-high-field imaging applications such as human brain functional MRI with physiologic noise correction may benefit from this method of ECG triggering. Key points Ultra-high field 7 Tesla cardiac MRI is challenging due to the impact of the magneto-hydrodynamic (MHD) effect causing severe distortions in the ECG trace. Using VCG with a learning phase outside the ultra-high field magnet, the R waves can be adequately detected to perform high quality Cardiac MRI scans, overcoming signal distortion from the MHD effect.