Dual flip angle liver T1 mapping with B1 correction at 3 T - In vitro and in vivo evaluation

To investigate the in vitro precision and linearity of 3D whole-liver covering dual flip angle (DFA) T1 mapping and compare different circular ROI sampling strategies in vivo.

All scans were performed at 3 T using a commercially available three-dimensional steady-state spoiled gradient echo with DFA. The in vitro study was performed on the EUROSPIN Test Object 5 with inversion recovery turbo spin echo (IRTSE) performed for reference T1 values. The in vivo study was performed in 30 patients before and after gadoxetic acid. In vitro DFA T1 map was compared to IRTSE T1 map voxel-by-voxel. In vivo DFA T1 maps were manually segmented for mean-segment T1. Two readers estimated segmental T1 using 4 ROI sampling strategies. Inter-reader agreement was assessed, and ROI sampling strategies were compared to manual segmentation. Linear regression, Bland-Altman plots and comparison of correlations were performed.

In vitro DFA T1 measurements showed strong linearity with R² = 0.9912 (P < 0.0001) compared to IRTSE with 16.33 % overestimation. In vivo ROI-based estimated segmental T1 demonstrated improved inter-reader agreement with R² increasing from 0.9135 to 0.9601 (P < 0.003) and narrower limits-of-agreement as the ROI area increased. Agreement with manual segmentation-based mean-segment T1 improved with increasing ROI area (R² 0.9718 to 0.9778 and 0.9359 to 0.9722, for reader 1 and 2 respectively) as well as narrower limits-of-agreement.

DFA T1 measurements had a strong linearity with a minor overestimation. The use of larger ROI areas leads to better agreement with manual segmentation and improved inter-reader agreement.