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

Purpose: Liver T1 mapping techniques typically require long breath holds or long scan time in free‐breathing, need correction for B1+ 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. Methods: 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, B1+ 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. Results: 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 B1+ 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 B1+ inhomogeneities (wT1,NoB1+=1.07wT1,B1+−45.63,R2=0.99), good repeatability (wT1,2°=1.0wT1,1°−2.14,R2=0.96) and is in better agreement with MRS (wT1=0.92wT1MRS+103.28,R2=0.38) than is MOLLI (wT1MOLLI=0.76wT1MRS+254.43,R2=0.44). The wT1 maps in patients captured diverse lesions, thus showing their clinical feasibility. Conclusion: 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 B1+ map. The proposed method is suitable for nine‐slice liver clinical applications acquired in a single breath hold of 11 s. [ABSTRACT FROM AUTHOR]