Single-Breathhold 3D MR Elastography in the Liver, With Simultaneous R2*and PDFF Mapping

Abstract

Purpose To develop a sequence for the rapid acquisition of MR elastography (MRE) parameters in 3D, with simultaneous measurement of proton-density fat fraction (PDFF) and R2* for multiparametric assessment of liver disease.Methods The proposed sequence uses an interleaved motion-encoding scheme to acquire 3D volumes of all motion encodings and wave offsets from a single series of readouts with constant repetition time. This leads to a highly time-efficient acquisition, which together with incoherent k-space undersampling permits all MRE data to be acquired in a single breathhold. The undersampled volumes are reconstructed using compressed sensing with model-based temporal regularisation. The sequence can be combined with a multi-echo readout to allow 3D PDFF and R2* maps to be reconstructed from the reference volume of the MRE acquisition. Validation was performed in phantoms and in eight healthy volunteers.Results Phantom measurements of all viscoelastic parameters, PDFF, and R2* corresponded closely with reference measurements. Average liver tissue parameter values acquired with the combined MRE, PDFF and R2* sequence at 3 T were 1.36 +/-$$ pm $$ 0.15 m/s for shear-wave speed, 1.78 +/-$$ pm $$ 0.41 kPa for the magnitude of the complex shear modulus, 0.70 +/-$$ pm $$ 0.16 kPa for the loss modulus, 3.6% +/-$$ pm $$ 1.0% for PDFF, and 46.9 +/-$$ pm $$ 7.3 s-1 for R2*.Conclusion Single-breathhold 3D MRE in the liver was achieved with a novel acquisition ordering. The sequence offers 3D elastograms from a 16-s breathhold, or 3D elastograms with co-registered PDFF and R2* maps from a 21-s breathhold.