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



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.



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).



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.
Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Florian
F
Dittmann
Institute of Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Sebastian
S
Hirsch
Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Heiko
H
Tzschätzsch
Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Jing
J
Guo
Institute of Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Jürgen
J
Braun
Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany. ingolf.sack@charite.de.
Ingolf
I
Sack
D000328:Adult; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging* / Q000502:physiology*; D055119:Elastic Modulus / Q000502:physiology; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008099:Liver / Q000000981:diagnostic imaging* / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D033081:Shear Strength / Q000502:physiology; D013314:Stress, Mechanical
brain; liver; low-frequency harmonic tissue stimulation; multifrequency dual elasto-visco MDEV inversion; three-dimensional; wideband MRE