In vivo wideband multifrequency MR elastography of the human brain and liver

Abstract

Purpose: To demonstrate the feasibility of in vivo wideband MR elastography (wMRE) using continuous, time-harmonic shear vibrations in the frequency range of 10–50 Hz. Theory and Methods: The method was tested in a gel phantom with marked mechanical loss. The brains and livers of eight volunteers were scanned by wMRE using multislice, single-shot MRE with optimized fractional encoding and synchronization of sequence acquisition to vibration. Multifrequency three-dimensional inversion was used to reconstruct compound maps of magnitude |G*| and phase φ of the complex shear modulus. A new phase estimation, φ*, was developed to avoid systematic bias due to noise. Results: In the phantom, G*-dispersion measured by wMRE agreed well with oscillatory shear rheometry. |G*| and φ* measured at vibrations of 10–25 HZ, 25–35 HZ, and 40–50 HZ were 0.62 ± 0.08, 1.56 ± 0.16, 2.18 ± 0.20 kPa and 0.09 ± 0.17, 0.39 ± 0.16, 0.20 ± 0.13 rad in brain and 0.89 ± 0.11, 1.67 ± 0.20, 2.27 ± 0.35 kPa and 0.15 ± 0.10, 0.24 ± 0.05, 0.26 ± 0.05 rad in liver. Elastograms including all frequencies showed the best resolution of anatomical detail with |G*| = 1.38 ± 0.12 kPa, φ* = 0.24 ± 0.10 rad (brain) and |G*| = 1.79 ± 0.23 kPa, φ* = 0.24 ± 0.05 rad (liver). Conclusion: wMRE reveals highly dispersive G* properties of the brain and liver, and our results suggest that the influence of large-scale structures such as fluid-filled vessels and sulci on the MRE-measured parameters increases at low vibration frequencies. Magn Reson Med 76:1116–1126, 2016. © 2015 Wiley Periodicals, Inc.