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

Objective: 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. Methods: 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. Results: 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. Conclusion: 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.