title: MR diffusion is sensitive to mechanical loading in human intervertebral disks ex vivo.
abstract: OBJECTIVE
  To use T2 and diffusion MR to determine the change in the mechanical function of human disks with increased degenerative state.
  
  
  METHODS
  Spatial changes in T2 and diffusion were quantified in five cadaveric human lumbar disks under compressive loads. Regression models were used to investigate the relationship between the change in MR parameters and the disk's dynamic and viscoelastic properties.
  
  
  RESULTS
  Compressive loading caused a significant reduction in the disk's mean diffusivity ([11.3 versus 9.7].10(-4) .mm(2) /s, P < 0.001) but little change in T2 (P < 0.05). Diffusivity and T2 were correlated with the disk's dynamic (P < 0.01 and P < 0.05) and long-term viscoelastic (P < 0.05 and P < 0.05) stiffness. Diffusivity but not T2, was correlated with its viscoelastic dampening (r(2) = 0.45, P < 0.01) and instantaneous stiffness (r(2) = 0.44, P < 0.05). Nucleus diffusivity was significantly higher than the annulus's (-21% to -4%, P < 0.01). MR-estimated hydration was correlated with the instantaneous viscoelastic stiffness of the nucleus (r(2) = 0.35, P < 0.05) and the dynamic (r(2) = 0.44, P < 0.05) and long-term viscoelastic (r(2) = 0.42, P < 0.05) stiffness in the annulus. T2 correlated with diffusivity at low load (r(2) = 0.66, P < 0.05), but not at high load.
  
  
  CONCLUSIONS
  The strong correlations between diffusivity and the rheological assessments of disk mechanics suggest that MR might permit quantitative assessment of disk functional status and structural integrity.
authors.affiliation: Center for Advanced Orthopedic Studies, Department of Orthopedics, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Ron N
authors.initials: RN
authors.lastname: Alkalay
authors.forename: Deborah
authors.initials: D
authors.lastname: Burstein
authors.forename: Carl-Fredrik
authors.initials: CF
authors.lastname: Westin
authors.forename: Dominick
authors.initials: D
authors.lastname: Meier
authors.forename: David B
authors.initials: DB
authors.lastname: Hackney
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology*; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000503:physiopathology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: MR diffusivity; T2 relaxation; degeneration; intervertebral disc; mechanical competence