3DMMRE: Combining spatial resolution with viscosity-sensitive MRE
Background: The acquisition of wave fields is a central point in MRE. High sensitivity to motion is required along with robust image quality and sufficient SNR. Moreover, MRE should be fast since the mechanical stimulation may be inconvenient for patients when exceeding certain time limits.
Problem: Currently, MRE is limited by long scan times and is therefore applied either by 2D MRE at four drive frequencies or by three-dimensional 3D MRE at single frequency. Multifrequency 2D MRE can assess the dynamics of the complex shear modulus but cannot provide field information. In contrast, 3D MRE provides the full vector field of the shear waves but is limited in the dynamic information.
Proposed solution: Single-shot echo-planar imaging (EPI) MRE with short echo times and fractional motion encoding  enables us to ultimately combine 3DMRE with multifrequency wave stimulation to 3D multifrequency MRE (3DMMRE). 3DMMRE is capable of high-resolution MRE by 3D multifrequency inversion , compression-sensitive MRE  or viscoelastic modeling as it was previously based on 2DMMRE . Thus, a single 3D-vector field multifrequency MRE-data set allows researchers to pursuit different strategies of analyzing the full information MRE can provide towards the precise diagnosis and characterization of in vivo soft tissue.
Figure 1: 3DMMRE of the abdomen. Shown are wave components in a transversal slice out of 10 slices at 7 different vibration frequencies. Total measure time (without pauses for respiration) was approximately 10 min.
 Rump J, Klatt D, Braun J, Warmuth C, Sack I. Fractional encoding of harmonic motions in MR elastography. Magn Reson Med 2007;57(2):388-395.
 Papazoglou S, Hirsch S, Braun J, Sack I. Multifrequency inversion in magnetic resonance elastography. Phys Med Biol 2012;57(8):2329-2346.
 Hirsch S, Klatt D, Freimann F, Scheel M, Braun J, Sack I. In vivo measurement of volumetric strain in the human brain induced by arterial pulsation and harmonic waves. Magn Reson Med 2012;doi: 10.1002/mrm.24499. [Epub ahead of print].
 Klatt D, Hamhaber U, Asbach P, Braun J, Sack I. Noninvasive assessment of the rheological behavior of human internal organs using multifrequency MR elastography: A study of brain and liver viscoelasticity. Phys Med Biol 2007;52(24):7281-7294.