3D Whole-Heart Joint T₁/T_1ρ Mapping and Water-Fat Imaging on a Clinical 0.55-T Low-Field Scanner

Myocardial maps are conventionally acquired in 2D breath-hold single-parameter scans that are slow and have limited heart coverage. To overcome limitations associated with 2D breath-hold mapping sequences, we develop a novel free-breathing 3D joint $T_1$ / $T_{1\rho }$ mapping sequence with Dixon encoding to provide co-registered 3D $T_1$ and $T_{1\rho }$ maps and water-fat volumes with isotropic spatial resolution in a single scan for comprehensive contrast-agent free myocardial tissue characterization and visualisation of the whole-heart anatomy on a clinical 0.55-T MR scanner. The proposed sequence acquires four interleaved 3D volumes with preparation modules to provide $T_1$ and $T_{1\rho }$ encoding, with data acquired with a two-echo Dixon readout and 2D image navigators to enable $100\%$ respiratory scan efficiency. Images were reconstructed with nonrigid respiratory motion-corrected iterative SENSE with multi-dimensional low-rank patch-based denoising, and maps generated by matching with simulated dictionaries. The proposed sequence was tested in phantoms, 11 healthy subjects and 1 patient, and compared with conventional techniques. For phantoms, the proposed 3D $T_1$ and $T_{1\rho }$ measurements showed good correlation with 2D spin-echo reference measurements. For healthy subjects, septal myocardial tissue mapping values were $T_1=743\pm 19\text{ms}$ and $T_{1\rho }=46.9\pm 2.7\text{ms}$ for the proposed sequence, against $T_1=681\pm 23\text{ms}$ and $T_{1\rho }=57.9\pm 3.6\text{ms}$ for 2D modified Look-Locker inversion recovery and 2D $T_{1\rho }$ respectively. Promising results were obtained when the proposed mapping was compared to 2D late-gadolinium enhancement imaging in a patient. The proposed approach enables simultaneous 3D whole-heart joint $T_1$ / $T_{1\rho }$ mapping and water-fat imaging at 0.55 T in a single scan of $\approx 11$ min, demonstrating good agreement with conventional techniques in phantoms and healthy subjects, and promising results in a patient.