title: Assessment of intervertebral disc degeneration based on quantitative magnetic resonance imaging analysis: an in vivo study.
abstract: METHODS
  Animal experimental study.
  
  
  OBJECTIVE
  To evaluate a novel quantitative imaging technique for assessing disc degeneration.
  
  
  BACKGROUND
  T2-relaxation time (T2-RT) measurements have been used to assess disc degeneration quanti-tatively. T2 values correlate with the water content of intervertebral disc tissue and thereby allow for the indirect measurement of nucleus pulposus (NP) hydration.
  
  
  METHODS
  We developed an algorithm to subtract out magnetic resonance imaging (MRI) voxels not representing NP tissue on the basis of T2-RT values. Filtered NP voxels were used to measure nuclear size by their amount and nuclear hydration by their mean T2-RT. This technique was applied to 24 rat-tail intervertebral discs (IVDs), which had been punctured with an 18-gauge needle according to different techniques to induce varying degrees of degeneration. NP voxel count and average T2-RT were used as parameters to assess the degeneration process at 1 and 3 months postpuncture. NP voxel counts were evaluated against radiograph disc height measurements and qualitative MRI studies on the basis of the Pfirrmann grading system. Tails were collected for histology to correlate NP voxel counts to histological disc degeneration grades and to NP cross-sectional area measurements.
  
  
  RESULTS
  NP voxel count measurements showed strong correlations to qualitative MRI analyses (R = 0.79, P < 0.0001), histological degeneration grades (R = 0.902, P < 0.0001), and histological NP cross-sectional area measurements (R = 0.887, P < 0.0001).In contrast to NP voxel counts, the mean T2-RT for each punctured group remained constant between months 1 and 3. The mean T2-RTs for the punctured groups did not show a statistically significant difference from those of healthy IVDs (63.55 ms ± 5.88 ms mo 1 and 62.61 ms ± 5.02 ms) at either time point.
  
  
  CONCLUSIONS
  The NP voxel count proved to be a valid parameter to assess disc degeneration quantitatively in a needle puncture model. The mean NP T2-RT does not change significantly in needle-puncture-induced degenerated IVDs. IVDs can be segmented into different tissue components according to their innate T2-RT.
authors.affiliation: *Weill Cornell Brain and Spine Institute, Department of Neurological Surgery, Weill Cornell Medical College, NYPH, New York, NY †Department of Biomedical Engineering, Cornell University, Ithaca, NY ‡Citigroup Biomedical Imaging Center, Weill Cornell Medical College, New York, NY; and §Department of Radiology, Weill Cornell Medical College, New York, NY.
authors.forename: Peter
authors.initials: P
authors.lastname: Grunert
authors.forename: Katherine D
authors.initials: KD
authors.lastname: Hudson
authors.forename: Michael R
authors.initials: MR
authors.lastname: Macielak
authors.forename: Eric
authors.initials: E
authors.lastname: Aronowitz
authors.forename: Brandon H
authors.initials: BH
authors.lastname: Borde
authors.forename: Marjan
authors.initials: M
authors.lastname: Alimi
authors.forename: Innocent
authors.initials: I
authors.lastname: Njoku
authors.forename: Douglas
authors.initials: D
authors.lastname: Ballon
authors.forename: Apostolos John
authors.initials: AJ
authors.lastname: Tsiouris
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Bonassar
authors.forename: Roger
authors.initials: R
authors.lastname: Härtl
mesh_terms: D000465:Algorithms; D000818:Animals; D004195:Disease Models, Animal; D007090:Image Interpretation, Computer-Assisted; D007403:Intervertebral Disc / Q000473:pathology*; D055959:Intervertebral Disc Degeneration / Q000175:diagnosis* / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D015588:Observer Variation; D011237:Predictive Value of Tests; D051381:Rats; D011923:Rats, Nude; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013997:Time Factors