Free-breathing multitasking multi-echo MRI for whole-liver water-specific T-1, proton density fat fraction, and R-2* quantification

Purpose: To develop a 3D multitasking multi-echo (MT-ME) technique for the comprehensive characterization of liver tissues with 5-min free-breathing acquisition; whole-liver coverage; a spatial resolution of 1.5 x 1.5 x 6 mm(3); and simultaneous quantification of T-1, water-specific T-1 (T-1w), proton density fat fraction (PDFF), and R-2*. Methods: Six-echo bipolar spoiled gradient echo readouts following inversion recovery preparation was performed to generate T-1, water/fat, and R-2* contrast. MR multitasking was used to reconstruct the MT-ME images with 3 spatial dimensions: 1 T-1 recovery dimension, 1 multi-echo dimension, and 1 respiratory dimension. A basis function-based approach was developed for T-1w quantification, followed by the estimation of R-2* and T-1-corrected PDFF. The intrasession repeatability and agreement against references of MT-ME measurements were tested on a phantom and 15 clinically healthy subjects. In addition, 4 patients with confirmed liver diseases were recruited, and the agreement between MT-ME measurements and references was assessed. Results: MT-ME produced high-quality, coregistered T-1, T-1w, PDFF, and R-2* maps with good intrasession repeatability and substantial agreement with references on phantom and human studies. The intra-class coefficients of T-1, T-1w, PDFF, and R-2* from the repeat MT-ME measurements on clinically healthy subjects were 0.989, 0.990, 0.999, and 0.988, respectively. The intra-class coefficients of T-1, PDFF, and in healthy subjects and 0.980, 0.999, and 0.998 in patients. The T-1w was independent to PDFF (R = -0.029, P = .904). Conclusion: The proposed MT-ME technique quantifies T-1, T-1w, PDFF, and R-2* simultaneously and is clinically promising for the comprehensive characterization of liver tissue properties.