  This work introduced a stack-of-radial multi-echo asymmetric-echo MRI
sequence for free-breathing liver volumetric acquisition. Regularized
model-based reconstruction was implemented in Berkeley Advanced Reconstruction
Toolbox (BART) to jointly estimate all physical parameter maps (water, fat,
R2*, and B0 field inhomogeneity maps) and coil sensitivity maps from self-gated
k-space data. Specifically, locally low rank and temporal total variation
regularization were employed directly on physical parameter maps. The proposed
free-breathing radial technique was tested on a water/fat & iron phantom, a
young volunteer, and obesity/diabetes/hepatic steatosis patients. Quantitative
fat fraction and R2* accuracy were confirmed by comparing our technique with
the reference breath-hold Cartesian scan. The multi-echo radial sampling
sequence achieves fast k-space coverage and is robust to motion. Moreover, the
proposed motion-resolved model-based reconstruction allows for free-breathing
liver fat and R2* quantification in multiple motion states. Overall, our
proposed technique offers a convenient tool for non-invasive liver assessment
with no breath holding requirement.
