Multiparametric Free-Breathing 3D Whole-Heart Cardiac MR for Anatomical Bright- and Black-Blood Imaging With...

Low-field MRI has recently gained interest due to its potential for increased accessibility, reduced cost, and improved safety. However, high-quality anatomical imaging and robust tissue characterization remains an active area of research, particularly when aiming for a simple, one-click scan that captures all relevant information in a single acquisition. Bright-blood imaging is widely used for visualizing cardiac structures and coronary arteries, whereas black-blood is optimal for delineating the myocardium, atrial and vessel walls. High-resolution imaging is required for the accurate detection and segmentation of small anatomical structures, such as the coronary arteries, to enable assessment of narrowing or blockages. Co-registered $T_1/T_2$ mapping enables quantitative myocardial tissue characterization, offering valuable clinical information for the detection of myocardial abnormalities. In this study, we sought to develop a novel free-breathing, motion-compensated 3D multi-contrast high-resolution cardiac MR sequence for simultaneous assessment of whole-heart cardiovascular anatomy via bright- and black-blood imaging and myocardial tissue quantification by joint $T_1$ and $T_2$ mapping at 0.55 T in a single scan. Data were acquired over six interleaved contrasts with various preparation modules using a variable flip angle bSSFP spiral-like readout with 2D image-based navigation for translational motion correction, resulting in a predictable acquisition time of $\approx 12$ min. Images were reconstructed using non-rigid motion corrected iterative sensitivity encoding followed by high-dimensional patch-based low-rank denoising, resulting in the acquisition, reconstruction and quantitative mapping time of $\approx 31$ min. In the phantom study, sequence performance was evaluated using correlation and Bland-Altman analysis against reference gold-standard and clinical mapping methods. In vivo, 3D bright- and black-blood volumes were assessed in multiple views, and vessel sharpness was quantified from multiplanar images. For joint $T_1/T_2$ mapping, bull's-eye plots were generated to evaluate the mean, standard deviation, and coefficient of variation for apical, mid-cavity, and basal segments, and results were summarized using violin plots. Differences between the proposed 3D sequence and established 2D methods were analyzed with a two-tailed $t$ -test. In the phantom study, a small positive bias in $T_1$ of $6.3\text{ms}$ was observed compared with inversion recovery spin-echo and $23.5\text{ms}$ with MOLLI, while for $T_2$ biases of $7.3\text{ms}$ compared with spin-echo and $0.8\text{ms}$ with $T_2$ prep bSSFP were found. In vivo, statistically similar $T_1$ values of $(648\pm 26)\text{ms}$ and $T_2$ values of $(56.9\pm 3.2)\text{ms}$ were obtained, with differences versus MOLLI of $-3\text{ms}\pm 15\text{ms}$ ( $p=0.75$ ) and versus $T_2$ prep bSSFP of $-0.5\text{ms}\pm 2.1\text{ms}$ ( $p=0.63$ ). The proposed sequence demonstrated high image quality and accurate mapping despite the inherent limitations of low-field strength, suggesting its feasibility for comprehensive cardiac assessment in resource-limited environments.