Simultaneous 3D T 1 $$ {\mathrm{T}}_1 $$ , T 2 $$ {\mathrm{T}}_2 $$ , and fat-signal-fraction mapping with...

To develop a framework for simultaneous three-dimensional (3D) mapping of $T_1$ , $T_2$ , and fat signal fraction in the liver at 0.55 T.

The proposed sequence acquires four interleaved 3D volumes with a two-echo Dixon readout. $T_1$ and $T_2$ are encoded into each volume via preparation modules, and dictionary matching allows simultaneous estimation of $T_1$ , $T_2$ , and $M_0$ for water and fat separately. 2D image navigators permit respiratory binning, and motion fields from nonrigid registration between bins are used in a nonrigid respiratory-motion-corrected reconstruction, enabling 100% scan efficiency from a free-breathing acquisition. The integrated nature of the framework ensures the resulting maps are always co-registered.

$T_1$ , $T_2$ , and fat-signal-fraction measurements in phantoms correlated strongly (adjusted $r^2>0.98$ ) with reference measurements. Mean liver tissue parameter values in 10 healthy volunteers were $427\pm 22$ , $47.7\pm 3.3\hspace{0.17em}\text{ms}$ , and $7\pm 2\%$ for $T_1$ , $T_2$ , and fat signal fraction, giving biases of $71$ , $-30.0\hspace{0.17em}\text{ms}$ , and $-5$ percentage points, respectively, when compared to conventional methods.

A novel sequence for comprehensive characterization of liver tissue at 0.55 T was developed. The sequence provides co-registered 3D $T_1$ , $T_2$ , and fat-signal-fraction maps with full coverage of the liver, from a single nine-and-a-half-minute free-breathing scan. Further development is needed to achieve accurate proton-density fat fraction (PDFF) estimation in vivo.