Cardiac Magnetic Resonance Fingerprinting for Simultaneous T1, T2, and Fat-Fraction Quantification at 0.55 T

Cardiac magnetic resonance fingerprinting (cMRF) has been shown to allow for simultaneous quantitative characterization of myocardial tissue in a single scan. While cMRF has been assessed at 1.5 T and 3 T, its application at 0.55 T has not been demonstrated yet. This study introduces an adapted version of a previously implemented Dixon cMRF sequence designed for simultaneous quantification of T1, T2, and fat fraction (FF) at 1.5 T, to be employed at 0.55 T within a single breath-hold scan. The sequence was developed using the Pulseq environment and employs a radial tiny golden angle acquisition with bipolar readout. Reconstruction was performed using low-rank inversion in combination with a high-dimensional patch-based regularization. The Dixon cMRF technique at 0.55 T was tested on standardized phantoms and 15 healthy volunteers (HVs). cMRF at 0.55 T was compared to spin-echo (SE) and proton density references from phantoms, as well as conventional T1, T2, and FF mapping sequences at 0.55 T. Intrasession and intersession variability was assessed in phantoms and a representative HV. Results showed a good correlation between the proposed cMRF T1, T2, and FF at 0.55 T and the phantom IR-SE references (R² ≥ 0.98 for T1 and T2, R² ≥ 0.97 for FF). Intrasession variability was low (8.9 ± 13.8 ms for T1, 0.1 ± 1 ms for T2, and 0.02 ± 0.03% for FF), as was intersession variability (8.2 ± 8.5 ms, 0.4 ± 1.1 ms, and 0.02 ± 0.25%, respectively). In vivo assessments yielded good map quality, with mean myocardial values of 714 ± 24 ms for T1, 49 ± 5.9 ms for T2, and 2.6 ± 0.9% for FF in comparison to 672 ± 40 for T1-MOLLI, 60 ± 5.4 for T2prep-bSSFP, and 4.7 ± 2.4% for 2-echo PDFF, respectively. The technique demonstrated good agreement for T1 and FF, but T2 was underestimated, which is consistent with findings at higher field strengths. Further investigation in a larger cohort of healthy subjects and in patients with cardiovascular disease is warranted.