Accelerated liver water T₁ mapping using single-shot continuous inversion-recovery spiral imaging

Liver T₁ mapping techniques typically require long breath holds or long scan time in free-breathing, need correction for $B_1^{+}$ inhomogeneities and process composite (water and fat) signals. The purpose of this work is to accelerate the multi-slice acquisition of liver water selective T₁ (wT₁) mapping in a single breath hold, improving the k-space sampling efficiency.

The proposed continuous inversion-recovery (IR) Look-Locker methodology combines a single-shot gradient echo spiral readout, Dixon processing and a dictionary-based analysis for liver wT₁ mapping at 3 T. The sequence parameters were adapted to obtain short scan times. The influence of fat, $B_1^{+}$ inhomogeneities and TE on the estimation of T₁ was first assessed using simulations. The proposed method was then validated in a phantom and in 10 volunteers, comparing it with MRS and the modified Look-Locker inversion-recovery (MOLLI) method. Finally, the clinical feasibility was investigated by comparing wT₁ maps with clinical scans in nine patients.

The phantom results are in good agreement with MRS. The proposed method encodes the IR-curve for the liver wT₁ estimation, is minimally sensitive to $B_1^{+}$ inhomogeneities and acquires one slice in 1.2 s. The volunteer results confirmed the multi-slice capability of the proposed method, acquiring nine slices in a breath hold of 11 s. The present work shows robustness to $B_1^{+}$ inhomogeneities ( ${\mathrm{wT}}_{1,\mathrm{No}{B}_1^{+}}=1.07{\mathrm{wT}}_{1,B_1^{+}}-45.63,R^2=0.99)$ , good repeatability ( ${\mathrm{wT}}_{1,2°}=1.0{\mathrm{wT}}_{1,1°}-2.14,R^2=0.96)$ and is in better agreement with MRS ( ${\mathrm{wT}}_1=0.92{\mathrm{wT}}_{1\mathrm{MRS}}+103.28,R^2=0.38)$ than is MOLLI ( ${\mathrm{wT}}_{1\text{MOLLI}}=0.76{\mathrm{wT}}_{1\mathrm{MRS}}+254.43,R^2=0.44)$ . The wT₁ maps in patients captured diverse lesions, thus showing their clinical feasibility.

A single-shot spiral acquisition can be combined with a continuous IR Look-Locker method to perform rapid repeatable multi-slice liver water T₁ mapping at a rate of 1.2 s per slice without a $B_1^{+}$ map. The proposed method is suitable for nine-slice liver clinical applications acquired in a single breath hold of 11 s.