Abstract
Cardiac magnetic resonance imaging at ultra-high field (B0 ≥ 7 T) potentially provides improved resolution and new opportunities for tissue characterization. Although an accurate synchronization of the acquisition to the cardiac cycle is essential, electrocardiogram (ECG) triggering at ultra-high field can be significantly impacted by the magnetohydrodynamic (MHD) effect. Blood flow within a static magnetic field induces a voltage, which superimposes the ECG and often affects the recognition of the R-wave. The MHD effect scales with B0 and is particularly pronounced at ultra-high field creating triggering-related image artifacts. Here, we investigated the performance of a conventional 3-lead ECG trigger device and a state-of-the-art trigger algorithm for cardiac ECG synchronization at 7 T. We show that by appropriate subject preparation and by including a learning phase for the R-wave detection outside of the magnetic field, reliable ECG triggering is feasible in healthy subjects at 7 T without additional equipment. Ultra-high field cardiac imaging was performed with the ECG signal and the trigger events recorded in 8 healthy subjects. Despite severe ECG signal distortions, synchronized imaging was successfully performed. Recorded ECG signals, vectorcardiograms, and large consistency in trigger event spacing indicate high accuracy for R-wave detection.
Highlights
Cardiovascular magnetic resonance (CMR) is an important and well-established clinical tool for the diagnosis and management of cardiovascular diseases, and it is the standard of reference for the evaluation of cardiac morphology and function [1,2,3]
Despite the significant impact of the MHD effect, the QRS complex is clearly identifiable in both channels and—as can be seen from the accurate alignment of the individual RR-intervals— has been accurately detected by the trigger algorithm for each of the displayed cardiac cycles
We explored the applicability of existing and state-of-the-art 3-lead ECG trigger technology for cardiac synchronization at the ultra-high field strength of 7 T
Summary
Cardiovascular magnetic resonance (CMR) is an important and well-established clinical tool for the diagnosis and management of cardiovascular diseases, and it is the standard of reference for the evaluation of cardiac morphology and function [1,2,3]. CMR relies on accurate cardiac gating alongside parallel imaging [4, 5], simultaneous multi-slice imaging [6,7,8], or other acceleration methods [9, 10] to address limitations due to motion. The fact remains that CMR must always make a tradeoff between spatiotemporal resolution and signal-to-noise ratio. Apart from enabling spatial resolutions that exceed today’s limits [16], CMR at ultra-high field offers new opportunities for magnetic resonance-based tissue characterization [17, 18] or metabolic imaging [19]
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