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In vivo wideband multifrequency MR elastography of the human brain and liver
Author(s) -
Dittmann Florian,
Hirsch Sebastian,
Tzschätzsch Heiko,
Guo Jing,
Braun Jürgen,
Sack Ingolf
Publication year - 2016
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26006
Subject(s) - magnetic resonance elastography , elastography , imaging phantom , materials science , nuclear magnetic resonance , in vivo , biomedical engineering , nuclear medicine , physics , acoustics , medicine , biology , ultrasound , microbiology and biotechnology
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.