title: In vivo magnetic resonance elastography of human brain at 7 T and 1.5 T.
abstract: OBJECTIVE
  To investigate the feasibility of quantitative in vivo ultrahigh field magnetic resonance elastography (MRE) of the human brain in a broad range of low-frequency mechanical vibrations.
  
  
  METHODS
  Mechanical vibrations were coupled into the brain of a healthy volunteer using a coil-driven actuator that either oscillated harmonically at single frequencies between 25 and 62.5 Hz or performed a superimposed motion consisting of multiple harmonics. Using a motion sensitive single-shot spin-echo echo planar imaging sequence shear wave displacements in the brain were measured at 1.5 and 7 T in whole-body MR scanners. Spatially averaged complex shear moduli were calculated applying Helmholtz inversion.
  
  
  RESULTS
  Viscoelastic properties of brain tissue could be reliably determined in vivo at 1.5 and 7 T using both single-frequency and multifrequency wave excitation. The deduced dispersion of the complex modulus was consistent within different experimental settings of this study for the measured frequency range and agreed well with literature data.
  
  
  CONCLUSIONS
  MRE of the human brain is feasible at 7 T. Superposition of multiple harmonics yields consistent results as compared to standard single-frequency based MRE. As such, MRE is a system-independent modality for measuring the complex shear modulus of in vivo human brain in a wide dynamic range.
authors.affiliation: Institute of Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany. uwe.hamhaber@biocer-gmbh.de
authors.forename: Uwe
authors.initials: U
authors.lastname: Hamhaber
authors.forename: Dieter
authors.initials: D
authors.lastname: Klatt
authors.forename: Sebastian
authors.initials: S
authors.lastname: Papazoglou
authors.forename: Maurice
authors.initials: M
authors.lastname: Hollmann
authors.forename: Jörg
authors.initials: J
authors.lastname: Stadler
authors.forename: Ingolf
authors.initials: I
authors.lastname: Sack
authors.forename: Johannes
authors.initials: J
authors.lastname: Bernarding
authors.forename: Jürgen
authors.initials: J
authors.lastname: Braun
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D054459:Elasticity Imaging Techniques / Q000379:methods*; D004558:Electric Stimulation / Q000379:methods; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D008962:Models, Theoretical; D012016:Reference Values; D014732:Vibration; D014783:Viscosity