Free-Breathing Myocardial T1 Mapping using Inversion-Recovery Radial FLASH and Motion-Resolved Model-Based Reconstruction

Purpose: To develop a free-breathing myocardial T1 mapping technique using free-running inversion-recovery (IR) radial fast low-angle shot (FLASH) and calibrationless motion-resolved model-based reconstruction. Methods: A free-running inversion-recovery radial FLASH sequence is used for data acquisition at 3T. To reduce the waiting time between inversions, an analytical formula is derived that takes the incomplete T1 recovery into account for an accurate T1 calculation. The respiratory motion signal is estimated from the filtered k-space center using an adapted singular spectrum analysis (SSA-FARY) technique. The cardiac motion signal is recorded using electrocardiography. A motion-resolved model-based reconstruction is used to estimate both parameter and coil sensitivity maps directly from the sorted k-space data. Spatial-temporal total variation, in addition to the spatial sparsity constraints, is applied to the parameter maps to improve T1 accuracy and precision. Validations are performed on an experimental phantom and five human subjects. Results: In comparison to an IR spin-echo reference, phantom results confirm good T1 accuracy when reducing the waiting time from five seconds to one second using the new correction. The motion-resolved model-based reconstruction further improves T1 precision. Aside from showing that a reliable respiratory motion signal can be estimated using modified SSA-FARY, in vivo studies with five healthy subjects demonstrate that high-resolution dynamic myocardial T1 maps (1.0x1.0x6 mm$^3$)can be obtained within two minutes with good T1 precision and repeatability. Conclusion: High-resolution motion-resolved T1 mapping during free-breathing with good T1 accuracy, precision, and repeatability can be achieved by combining inversion-recovery radial FLASH, self-gating, and a calibrationless motion-resolved model-based reconstruction.