Free-breathing multitasking multi-echo MRI for whole-liver water-specific T₁ , proton density fat fraction, and $R_2^{\ast }$ 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 × 1.5 × 6 mm³ ; and simultaneous quantification of T₁ , water-specific T₁ (T_1w ), proton density fat fraction (PDFF), and $R_2^{\ast }$ .

Methods: Six-echo bipolar spoiled gradient echo readouts following inversion recovery preparation was performed to generate T₁ , water/fat, and $R_2^{\ast }$ contrast. MR multitasking was used to reconstruct the MT-ME images with 3 spatial dimensions: 1 T₁ 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 $R_2^{\ast }$ and T₁ -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 T₁ , T_1w , PDFF, and $R_2^{\ast }$ maps with good intrasession repeatability and substantial agreement with references on phantom and human studies. The intra-class coefficients of T₁ , T_1w , PDFF, and $R_2^{\ast }$ 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 T₁ , PDFF, and $R_2^{\ast }$ between the MT-ME and reference measurements were 0.924, 0.987, and 0.975 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 T₁ , T_1w , PDFF, and $R_2^{\ast }$ simultaneously and is clinically promising for the comprehensive characterization of liver tissue properties.