Correlations between quantitative T2 and T1ρ MRI, mechanical properties and biochemical composition in a rabbit lumbar intervertebral disc degeneration model.
Improved diagnostic measures for intervertebral disc degeneration are necessary to facilitate early detection and treatment. The aim of this study was to correlate changes in mechanical and biochemical properties with the quantitative MRI parameters T2 and T1ρ in rabbit lumbar discs using an ex vivo chymopapain digestion model. Rabbit lumbar spinal motion segments from animals less than 6 months of age were injected with 100 μl of saline (control) or chymopapain at 3, 15, or 100 U/ml (n = 5 per group). T2 and T1ρ MRI series were obtained at 4.7T. Specimens were mechanically tested in tension-compression and creep. Normalized nucleus pulposus (NP) water and GAG contents were quantified. Stepwise multiple linear regression was performed to determine which parameters contributed significantly to changes in NP T2 and T1ρ. When all groups were included, multiple regression yielded a model with GAG, compressive modulus, and the creep time constants as variables significantly impacting T2 (multiple r(2)  = 0.64, p = 0.006). GAG and neutral zone (NZ) modulus were identified as variables contributing to T1ρ (multiple r(2)  = 0.28, p = 0.08). When specimens with advanced degeneration were excluded from the multiple regression analysis, T2 was significantly predicted by compressive modulus, τ1, and water content (multiple r(2)  = 0.71, p = 0.009), while no variables were significant predictors in the model for T1ρ. These results indicate that quantitative MRI can detect changes in the mechanical and biochemical properties of the degenerated disc. T2 may be more sensitive to early stage degenerative changes than T1ρ, while both quantitative MRI parameters are sensitive to advanced degeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1382-1388, 2016.
Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania.|Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania.
Sarah E
SE
Gullbrand
Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania.
Beth G
BG
Ashinsky
Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania.|Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania.
John T
JT
Martin
Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania.
Stephen
S
Pickup
Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania.|Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania.|Department of Neurosurgery, University of Pennsylvania, Philadelphia, Pennsylvania.
Lachlan J
LJ
Smith
Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania.|Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania.
Robert L
RL
Mauck
Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania.|Translational Musculoskeletal Research Center, Philadelphia VA Medical Center, Philadelphia, Pennsylvania.
Harvey E
HE
Smith
D000818:Animals; D001696:Biomechanical Phenomena; D002917:Chymopapain; D004195:Disease Models, Animal; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging*; D008159:Lumbar Vertebrae / Q000737:chemistry / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011817:Rabbits
D002917:Chymopapain
T1ρ; T2; biomechanics; intervertebral disc degeneration; magnetic resonance imaging