title: In vivo multifrequency magnetic resonance elastography of the human intervertebral disk.
abstract: OBJECTIVE
  To test in vivo magnetic resonance elastography (MRE) of the human intervertebral disk (IVD).
  
  
  METHODS
  The feasibility of MRE in IVD was demonstrated in ex vivo bovine disks. Sixteen asymptomatic volunteers underwent multifrequency MRE of the lumbar spine (IVD L3/4 and L4/5, n = 32) using a posterior plate transducer connected to a loudspeaker and operated at five frequencies from 50 to 70 Hz. Full wave field data were acquired in 10 transverse slices of 2 × 2 × 2 mm(3) resolution. High-resolution maps of magnitude |G*| and phase angle φ of complex shear modulus G* were generated by multifrequency dual elasto visco (MDEV) inversion. Disk morphology was assessed by the Pfirrmann score (Pf).
  
  
  RESULTS
  Morphological Pf was 1 in 25, 2 in 3, and 3 in 4 disks. |G*| decreased with Pf by a Pearson's linear correlation coefficient of R = -0.592 (P = 0.0004), while φ remained unchanged. Group mean mechanical parameters for Pf = 1 to 3 were |G*| = 6.51 ± 1.27, 5.29 ± 0.95, 4.03 ± 0.99 kPa, and φ = 1.190 ± 0.181, 1.170 ± 0.156, 1.088 ± 0.084 rad, respectively (p[Pf1-Pf3] < 0.001). The variability of mechanical parameters in one volunteer including diurnal changes was approximately 11%.
  
  
  CONCLUSIONS
  Multifrequency MRE with MDEV inversion allows measurement of in vivo mechanical properties of IVDs and may provide additional information in disc degeneration beyond standard morphological changes.
authors.affiliation: Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Kaspar-Josche
authors.initials: KJ
authors.lastname: Streitberger
authors.affiliation: Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Diederichs
authors.affiliation: Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Jing
authors.initials: J
authors.lastname: Guo
authors.affiliation: Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Fehlner
authors.affiliation: Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Hamm
authors.affiliation: Institute of Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Braun
authors.affiliation: Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Ingolf
authors.initials: I
authors.lastname: Sack
mesh_terms: D000328:Adult; D000818:Animals; D002417:Cattle; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007403:Intervertebral Disc / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results
keywords: MRE; high resolution; intervertebral disks; magnetic resonance elastography; magnitude shear modulus; multifrequency dual elasto visco inversion; phase angle