Free-breathing, fat-corrected T mapping of the liver with stack-of-stars MRI, and joint estimation of T, PDFF, , and .

Purpose: Quantitative T mapping has the potential to replace biopsy for noninvasive diagnosis and quantitative staging of chronic liver disease. Conventional T mapping methods are confounded by fat and inhomogeneities, resulting in unreliable T estimations. Furthermore, these methods trade off spatial resolution and volumetric coverage for shorter acquisitions with only a few images obtained within a breath-hold. This work proposes a novel, volumetric (3D), free-breathing T mapping method to account for multiple confounding factors in a single acquisition.

Theory And Methods: Free-breathing, confounder-corrected T mapping was achieved through the combination of non-Cartesian imaging, magnetization preparation, chemical shift encoding, and a variable flip angle acquisition. A subspace-constrained, locally low-rank image reconstruction algorithm was employed for image reconstruction. The accuracy of the proposed method was evaluated through numerical simulations and phantom experiments with a T/proton density fat fraction phantom at 3.0 T. Further, the feasibility of the proposed method was investigated through contrast-enhanced imaging in healthy volunteers, also at 3.0 T.

Results: The method showed excellent agreement with reference measurements in phantoms across a wide range of T values (200 to 1000 ms, slope = 0.998 (95% confidence interval (CI) [0.963 to 1.035]), intercept = 27.1 ms (95% CI [0.4 54.6]), r = 0.996), and a high level of repeatability. In vivo imaging studies demonstrated moderate agreement (slope = 1.099 (95% CI [1.067 to 1.132]), intercept = -96.3 ms (95% CI [-82.1 to -110.5]), r = 0.981) compared to saturation recovery-based T maps.

Conclusion: The proposed method produces whole-liver, confounder-corrected T maps through simultaneous estimation of T, proton density fat fraction, and in a single, free-breathing acquisition and has excellent agreement with reference measurements in phantoms.