Navigator‐gated free‐breathing 2D radial cardiac joint T 1 – T 2 mapping

Abstract Purpose To implement a navigator‐gated free‐breathing 2D radial joint T 1 –T 2 mapping technique for the myocardium at 3T, and to characterize the impact of the navigator rejection on the precision and accuracy of the T 1 and T 2 maps. Methods The proposed technique, named PARMANav (for PArametric Radial Mapping with Navigator gating), collects 25 lung–liver navigator‐gated electrocardiogram (ECG)‐triggered single‐shot radial gradient‐recalled echo (GRE) images with five magnetization preparations. Source images were reconstructed using compressed sensing. Extended‐phase‐graph simulations were used to generate an acquisition‐specific joint T 1 –T 2 dictionary. The impact of the number of rejected navigators on the relaxation times was assessed in numerical simulations. The influence of the navigator acceptance window width (NAWW) and heart rate on the relaxation times was assessed in phantom studies, 10 healthy volunteers, and 3 patients. The relaxation times were compared to routine T 1 and T 2 mapping values. Results The numerical simulations showed negligible dependence on the number of rejected navigators (<6% T 1 –T 2 variation). In the phantom, PARMANav T 1 –T 2 values were stable across heart rates: the T 1 –T 2 coefficient of variation (CoV) was <3%. As expected from literature, in‐vivo PARMANav T 1 –T 2 values were higher than routine values (T 1 = 1331 ± 53 ms, T 2 = 46.1 ± 2.5 ms vs. T 1 = 1095 ± 81 ms, T 2 = 38.7 ± 2.9 ms, p < 0.001), while the PARMANav T 2 CoV was significantly reduced. No myocardial T 1 –T 2 values or CoV trend was observed for the different NAWW. Feasibility in patients was demonstrated, where high‐quality maps were obtained. Conclusion PARMANav allows for precise and accurate joint T 1 –T 2 mapping without requiring breath holding. Through‐plane motion artifacts were avoided with a navigator that did not impact the accuracy or precision of the resulting maps.