Simultaneous MR elastography and diffusion acquisitions: Diffusion-MRE (dMRE)

Abstract

To present a new technique for concurrent MR elastography (MRE) and diffusion MRI: diffusion-MRE (dMRE). In dMRE, shear wave motion and MR signal decay due to diffusion are encoded into the phase and magnitude components of the MR signal by using a pair of bipolar gradients for both motion-sensitization and diffusion encoding. The pulse sequence timing is adjusted so that the bipolar gradients are sensitive to both coherent and incoherent intravoxel motions. The shape, number, and duration of the gradient lobes can be adjusted to provide flexibility and encoding efficiency. In this proof-of-concept study, dMRE was validated using a tissue phantom composed of a gel bead embedded in a hydrated mixture of agarose and gelatin. The apparent diffusion coefficient (ADC) and shear stiffness measured using dMRE were compared with results obtained from separate, conventional spin-echo (SE) diffusion and SE-MRE acquisitions. The averaged ADC values (n = 3) for selected ROIs in the beads were (1.75 ± 0.16) μm(2) /ms and (1.74 ± 0.16) μm(2) /ms for SE-diffusion and dMRE methods, respectively. The corresponding shear stiffness values in the beads were (2.45 ± 0.23) kPa and (2.42 ± 0.20) kPa. Simultaneous MRE and diffusion acquisition is feasible and can be implemented with no observable interference between the two methods.