Myocardial Approximate Spin-lock Dispersion Mapping using a Simultaneous $T_{2}$ and $T_{RAFF2}$ Mapping at 3T MRI

Ischemic heart disease (IHD) is one of the leading causes of death worldwide. Myocardial infarction (MI) represents a third of all IHD cases, and cardiac magnetic resonance imaging (MRI) is often used to assess its damage to myocardial viability. Late gadolinium enhancement (LGE) is the current gold standard, but the use of gadolinium-based agents limits the clinical applicability in some patients. Spin-lock (SL) dispersion has recently been proposed as a promising non-contrast biomarker for the assessment of MI. However, at 3T, the required range of SL preparations acquired at different amplitudes suffers from specific absorption rate (SAR) limitations and off-resonance artifacts. Relaxation Along a Fictitious Field (RAFF) is an alternative to SL preparations with lower SAR requirements, while still sampling relaxation in the rotating frame. In this study, a single breath-hold simultaneous $T_{RAFF2}$ and $T_{2}$ mapping sequence is proposed for SL dispersion mapping at 3T. Excellent reproducibility (coefficient of variations lower than 10%) was achieved in phantom experiments, indicating good intrascan repeatability. The average myocardial $T_{RAFF2}, T_{2}$, and SL dispersion obtained with the proposed sequence $(68.0\pm 10.7$ ms, $44.0\pm 4.0$ ms, and $0.4\pm 0.2 \times 10^{-4} s^{2}$, respectively) were comparable to the reference methods $(62.7\pm 11.7$ ms, $41.2\pm 2.4$ ms, and $0.3\pm 0.2\mathrm{x} 10^{-4}s^{2}$, respectively). High visual map quality, free of $B_{0}$ and $B_{1}^{+}$ related artifacts, for $T_{2}, T_{RAFF2}$, and SL dispersion maps were obtained in phantoms and in vivo, suggesting promise in clinical use at 3T. Clinical relevance — and imaging promises non-contrast assessment of scar and focal fibrosis in a single breath-hold using approximate spin-lock dispersion mapping.