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

PurposeTo develop and evaluate a free-breathing 2D radial joint T-T2 mapping technique for the kidneys at 3T, and to assess the impact of navigator gating parameters on mapping precision and accuracy. MethodsThe 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 T-T2 dictionary was generated using extended phase graph simulations. T1 and T2 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 T1 and T2 precision were established in 10 healthy volunteers and were compared to routine T1 and T2 mapping. Three patients were scanned to demonstrate clinical feasibility. ResultsIn the phantom, PARMANav T1 and T2 values showed high accuracy with the gold standard T1 and T2 values and were insensitive to rejected navigators (< 5% variation for T1 and T2). As expected from previous studies, in-vivo renal PARMANav T1 and T2 values were higher than routine values but showed lower variability, both per subject and between subjects: in the cortex PARMANav T1=1601{+/-}48ms/T2=90.8{+/-}5.0ms vs routine T1=1307{+/-}108ms/T2=73.3{+/-}8.0ms, while in the medulla PARMANav T1=2044{+/-}82ms/T2 =90.3{+/-}5.4ms and routine T1=1560{+/-}122ms/T2=67.6{+/-}5.8ms. No T1 or T2 trend was observed for the different NAWW. Feasibility was demonstrated in patients, where high-quality maps were obtained. ConclusionPARMANav allows for precise and accurate joint T1-T2 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.