Navigator-gated free-breathing joint T 1 -T 2 mapping of the kidney
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Purpose
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 precision and accuracy.
Methods
The PARMANav sequence (PArametric Radial MApping with Navigator gating) was implemented for renal imaging, using 25 single-shot radial gradient echo acquisitions with five repeated magnetization preparations and lung-liver navigator gating to avoid through-plane motion. Virtual compressed coil and compressed sensing with spatial and contrast regularization was used for image reconstruction, followed by a model-based registration. An acquisition-specific joint T₁-T₂ dictionary was generated using extended phase graph simulations. T 1 and T 2 accuracies were quantified in a phantom study versus gold standard spin-echo-based sequences. The influence of the navigator acceptance window width (NAWW) and navigator rejection on T 1 and T 2 precision were established in 10 healthy volunteers and were compared to routine T 1 and T 2 mapping. Three patients were scanned to demonstrate clinical feasibility.
Results
In the phantom, PARMANav T 1 and T 2 values showed high accuracy with the gold standard T 1 and T 2 values and were insensitive to rejected navigators (< 5% variation for T 1 and T 2 ). As expected from previous studies, in-vivo renal PARMANav T 1 and T 2 values were higher than routine values but showed lower variability, both per subject and between subjects: in the cortex PARMANav T 1 =1601±48ms/T 2 =90.8±5.0ms vs routine T 1 =1307±108ms/T 2 =73.3±8.0ms, while in the medulla PARMANav T 1 =2044±82ms/T 2 =90.3±5.4ms and routine T 1 =1560±122ms/T 2 =67.6±5.8ms. No T 1 or T 2 trend was observed for the different NAWW. Feasibility was demonstrated in patients, where high-quality maps were obtained.
Conclusion
PARMANav allows for precise and accurate joint T 1 -T 2 mapping of the kidneys without requiring breath holding. Through-plane motion artifacts were avoided with a navigator, which did not impact the accuracy or precision of the resulting maps.
