title: Population average T2 MRI maps reveal quantitative regional transformations in the degenerating rabbit intervertebral disc that vary by lumbar level.
abstract: Magnetic resonance imaging (MRI) with T2-weighting is routinely performed to assess intervertebral disc degeneration. Standard clinical evaluations of MR images are qualitative, however, and do not focus on region-specific alterations in the disc. Utilizing a rabbit needle puncture model, T2 mapping was performed on injured discs to develop a quantitative description of the degenerative process following puncture. To do so, an 18G needle was inserted into four discs per rabbit (L3/L4 to L6/L7) and T2 maps were generated pre- and 4 weeks post-injury. Individual T2 maps were normalized to a disc-specific coordinate system and then averaged for pre- and post-injury population composite T2 maps. We also developed a method to automatically segment the nucleus pulposus by fitting the NP region of the T2 maps with modified 2-D and 3-D Gaussian distribution functions. Puncture injury produced alterations in MR signal intensity in a region-specific manner mirroring human degeneration. Population average T2 maps provided a quantitative representation of the injury response, and identified deviations of individual degenerate discs from the pre-injury population. We found that the response to standardized injury was modest at lower lumbar levels, likely as a result of increased disc dimensions. These tools will be valuable for the quantitative characterization of disc degeneration in future clinical and pre-clinical studies.
authors.affiliation: Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania; Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: John T
authors.initials: JT
authors.lastname: Martin
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Collins
authors.forename: Kensuke
authors.initials: K
authors.lastname: Ikuta
authors.forename: Robert L
authors.initials: RL
authors.lastname: Mauck
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Elliott
authors.forename: Yeija
authors.initials: Y
authors.lastname: Zhang
authors.forename: D Greg
authors.initials: DG
authors.lastname: Anderson
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Vaccaro
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Albert
authors.forename: Vincent
authors.initials: V
authors.lastname: Arlet
authors.forename: Harvey E
authors.initials: HE
authors.lastname: Smith
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D016011:Normal Distribution; D011817:Rabbits; D011859:Radiography; D012680:Sensitivity and Specificity
keywords: MRI; T2 mapping; degeneration; intervertebral disc; rabbit