Navigator-gated free-breathing joint T₁-T₂ mapping of the kidney

To develop and evaluate a free-breathing 2D radial joint T₁-T₂ mapping technique for the kidneys at 3T, and to assess the impact of navigator gating parameters on mapping accuracy in a phantom and precision in healthy volunteers.

The PARMANav sequence (PArametric Radial MApping with Navigator gating) was implemented with 25 single-shot radial gradient-echo acquisitions with five magnetization preparations and lung-liver navigator gating to avoid through-plane motion. Images were reconstructed using region-optimized virtual coils and compressed sensing, followed by model-based registration. An acquisition-specific joint T₁-T₂ dictionary was generated using extended phase-graph simulations. T₁-T₂ accuracy was quantified in a phantom and T₁-T₂ precision was established in 10 healthy volunteers. Three patients were scanned to demonstrate clinical feasibility.

In the phantom, PARMANav T₁-T₂ accuracy was high and insensitive to rejected navigators (< 5% variation for T₁ and T₂). In vivo PARMANav T₁ and T₂ values were higher than routine values but less variable, both per subject and between subjects: cortex PARMANav T₁ = 1601 ± 48 ms/T₂ = 90.8 ± 5.0 ms vs routine T₁ = 1307 ± 108 ms/T₂ = 73.3 ± 8.0 ms, medulla PARMANav T₁ = 2044 ± 82 ms/T₂ = 90.3 ± 5.4 ms and routine T₁ = 1560 ± 122 ms/T₂ = 67.6 ± 5.8 ms. No T₁ or T₂ trend was observed for the different NAWW. High-quality maps were obtained in the patients.

With accuracy confirmed in the phantom study and precision demonstrated in volunteers, PARMANav allows for precise and accurate renal joint T₁-T₂ mapping during free-breathing while minimizing through-plane motion.