Free‐breathing high isotropic resolution quantitative susceptibility mapping (QSM) of liver using 3D multi‐echo UTE cones acquisition and respiratory motion‐resolved image reconstruction.

Purpose: To enable free‐breathing and high isotropic resolution liver quantitative susceptibility mapping (QSM) using 3D multi‐echo UTE cones acquisition and respiratory motion‐resolved image reconstruction. Methods: Using 3D multi‐echo UTE cones MRI, a respiratory motion was estimated from the k‐space center of the imaging data. After sorting the k‐space data with estimated motion, respiratory motion state‐resolved reconstruction was performed for multi‐echo data followed by nonlinear least‐squares fitting for proton density fat fraction (PDFF), R2*$$ {\mathrm{R}}_2^{\ast } $$, and fat‐corrected B0 field maps. PDFF and B0 field maps were subsequently used for QSM reconstruction. The proposed method was compared with motion‐averaged (gridding) reconstruction and conventional 3D multi‐echo Cartesian MRI in moving gadolinium phantom and in vivo studies. Region of interest (ROI)‐based linear regression analysis was performed on these methods to investigate correlations between gadolinium concentration and QSM in the phantom study and between R2*$$ {\mathrm{R}}_2^{\ast } $$ and QSM in in vivo study. Results: Cones with motion‐resolved reconstruction showed sharper image quality compared to motion‐averaged reconstruction with a substantial reduction of motion artifacts in both moving phantom and in vivo studies. For ROI‐based linear regression analysis of the phantom study, susceptibility values from cones with motion‐resolved reconstruction (QSMppm$$ {\mathrm{QSM}}_{\mathrm{ppm}} $$ = 0.31 ×gadoliniummM+$$ \times {\mathrm{gadolinium}}_{\mathrm{mM}}+ $$ 0.05, R2$$ {R}^2 $$ = 0.999) and Cartesian without motion (QSMppm$$ {\mathrm{QSM}}_{\mathrm{ppm}} $$ = 0.32 ×gadoliniummM+$$ \times {\mathrm{gadolinium}}_{\mathrm{mM}}+ $$ 0.04, R2$$ {R}^2 $$ = 1.000) showed linear relationships with gadolinium concentrations and showed good agreement with each other. For in vivo, motion‐resolved reconstruction showed higher goodness of fit (QSMppm$$ {\mathrm{QSM}}_{\mathrm{ppm}} $$ = 0.00261 ×R2s−1*−$$ \times {\mathrm{R}}_{2_{{\mathrm{s}}^{-1}}}^{\ast }- $$ 0.524, R2$$ {R}^2 $$ = 0.977) compared to motion‐averaged reconstruction (QSMppm$$ {\mathrm{QSM}}_{\mathrm{ppm}} $$ = 0.0021 ×R2s−1*−$$ \times {\mathrm{R}}_{2_{{\mathrm{s}}^{-1}}}^{\ast }- $$ 0.572, R2$$ {R}^2 $$= 0.723) in ROI‐based linear regression analysis between R2*$$ {\mathrm{R}}_2^{\ast } $$ and QSM. Conclusion: Feasibility of free‐breathing liver QSM was demonstrated with motion‐resolved 3D multi‐echo UTE cones MRI, achieving high isotropic resolution currently unachievable in conventional Cartesian MRI. [ABSTRACT FROM AUTHOR]