Navigator-gated free-breathing 2D radial cardiac joint T₁-T₂ mapping

To implement a navigator-gated free-breathing 2D radial joint T₁-T₂ mapping technique for the myocardium at 3T, and to characterize the impact of the navigator rejection on the precision and accuracy of the T₁ and T₂ maps.

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 T₁-T₂ 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 T₁ and T₂ mapping values.

The numerical simulations showed negligible dependence on the number of rejected navigators (<6% T₁-T₂ variation). In the phantom, PARMANav T₁-T₂ values were stable across heart rates: the T₁-T₂ coefficient of variation (CoV) was <3%. As expected from literature, in-vivo PARMANav T₁-T₂ values were higher than routine values (T₁ = 1331 ± 53 ms, T₂ = 46.1 ± 2.5 ms vs. T₁ = 1095 ± 81 ms, T₂ = 38.7 ± 2.9 ms, p < 0.001), while the PARMANav T₂ CoV was significantly reduced. No myocardial T₁-T₂ values or CoV trend was observed for the different NAWW. Feasibility in patients was demonstrated, where high-quality maps were obtained.

PARMANav allows for precise and accurate joint T₁-T₂ 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.