Influence of Field Strength on CMR

Abstract

The twofold increase in the equilibrium net magnetisation at 3.0 T theoretically leads to a doubling in signal-to-noise ratio (SNR) in comparison to that at 1.5 T. In general, this can be traded for an increase in spatial resolution or in combination with parallel imaging it can be used to allow a reduction in image acquisition time or to improve the temporal resolution of functional imaging techniques. T1 relaxation times are significantly increased at 3.0 T, which leads to improved tag persistence for myocardial tagging techniques, improved background tissue suppression for MRA, and improved contrast for late gadolinium enhancement (LGE) and myocardial perfusion imaging. Drawbacks of imaging at 3.0 T include increased ECG artefacts, increased magnetic susceptibility artefacts, (most notably off-resonance banding artefacts on bSSFP pulse sequences), higher specific absorption rates (SAR) leading to increased tissue heating, RF field inhomogeneity, and greater safety restrictions relating to implanted devices. These drawbacks have presented a technical challenge to MR manufacturers, leading to the development of a number of solutions, including vector-cardiogram (VCG) triggering, resonant frequency scouts, high order shimming, and multi-channel RF body transmitter coils. All the CMR techniques used at 1.5 T can be applied at 3.0 T, each with some advantages and disadvantages.