Abstract
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 T1 / T1ρ mapping sequence with Dixon encoding to provide co-registered 3D T1 and T1ρ 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 T1 and T1ρ 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 T1 and T1ρ measurements showed good correlation with 2D spin-echo reference measurements. For healthy subjects, septal myocardial tissue mapping values were T1 = 743 ± 19 ms and T1ρ = 46.9 ± 2.7 ms for the proposed sequence, against T1 = 681 ± 23 ms and T1ρ = 57.9 ± 3.6 ms for 2D modified Look-Locker inversion recovery and 2D T1ρ 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 T1 / T1ρ mapping and water-fat imaging at 0.55 T in a single scan of ≈ 11 min, demonstrating good agreement with conventional techniques in phantoms and healthy subjects, and promising results in a patient.