7-Tesla Cardiac MRI for Ventricular and Valvular quantitation in healthy volunteers

Abstract

Background: Ultra-high-field (B0 ≥7 Tesla) cardiovascular magnetic resonance (CMR) offers increased resolution, but cardiac imaging requiring ECG gating is significantly impacted from the magneto-hydrodynamic (MHD) effect, distorts the ECG trace (1–3). Previously, 7T CMR was constrained to using pulse oximetry for triggering, We explored the technical feasbility of a 7 T research MR scanner using of-the-art ECG trigger algorithm to assess left and right ventricular volumes, aortic and pulmonary valve flow.

Methods: 7T CMR scans were performed on 10 healthy volunteers on whole-body research MRI scanner (Siemens Healthcare, Erlangen, Germany) with 8 channel Tx/32 channel Rx cardiac coil (MRI Tools GmbH, Berlin, Germany) under institutional review board approval. Vectorcardiogram ECG was successfully performed using a learning phase outside of the magnetic field, with a trigger algorithm with sufficient accuracy for CMR despite severe ECG signal distortions from the 7T field. Cine CMR was performed after 3rd-order B0 shimming using a high-resolution breath-held ECG-retro-gated segmented two-dimensional spoiled gradient echo sequence, and 2-dimensional phase contrast flow imaging. Analysis was performed using Cmr42 software (Circle CVi, Calgary).

Results: Successful 7T CMR scans were acquired in all patients (100%) using the Vectorcardiogram 3-lead ECG method. Image quality was sufficient to quantitate both left and right ventricular volumes, ejection fraction, aortic and pulmonary blood flow and regurgitant fractions in 9/10 (90%) of volunteers (figure 1), with one volunteer having difficulty with breath-holding and ventricular ectopy causing gating artefacts.