Relationship Between Quantitative MRI and Radiological, Histological, and Biochemical Measures of Intervertebral Disc...

Client-owned dogs presenting clinically with intervertebral disc disease (IVDD) are a potential comparative animal model to help advance the understanding of disc degeneration and its treatment. To utilize dog patients as a model, noninvasive imaging techniques are needed that can characterize subtle and progressive changes in disc health in longitudinal and treatment efficacy studies. The purpose of this study was to assess the sensitivity of quantitative MRI techniques in detecting disc degeneration in client-owned, nonchondrodystrophic-breed dogs.

Thoracolumbar vertebral columns from the donated bodies of 15 dogs without a history of IVDD were imaged at 3T MRI. Quantitative MRI maps (T2, T2*, T1ρ, adiabatic T1ρ, adiabatic T2ρ, and ADC) were acquired axially for 10 discs (T11-T12 to L7-S1), and median values were measured in the nucleus pulposus and annulus fibrosus. Four disc health measures (Pfirrmann grade, histology score, water content, and glycosaminoglycan content) were evaluated for each disc. The quantitative MRI and disc health measures were compared using linear models, and partial correlations (R _partial) were calculated.

Most dogs had both relatively healthy and degenerated discs as assessed by Pfirrmann grade and histology score. Quantitative MRI values in relatively healthy discs varied greatly between dogs but were similar across disc levels. In the nucleus pulposus, T2 relaxation times were moderately correlated with Pfirrmann grade (R _partial = -0.62; p < 0.0001), histology score (R _partial = -0.63; p < 0.0001), and water content (R _partial = +0.45; p < 0.0001), and weakly correlated with glycosaminoglycan content (R _partial = +0.31; p = 0.0047). T2, T2*, T1ρ, adiabatic T1ρ, and adiabatic T2ρ had similar relationships to the disc health measures in the nucleus pulposus. No notable relationships were observed with ADC or in the annulus fibrosus.

Quantitative T2, T2*, T1ρ, adiabatic T1ρ, and adiabatic T2ρ relaxation time mapping techniques are similarly related to radiological and histological measures of disc health and water and glycosaminoglycan content in nonchondrodystrophic-breed dogs.