Assessment of human disc degeneration and proteoglycan content using T1rho-weighted magnetic resonance imaging

Abstract

Study design: T1rho relaxation was quantified and correlated with intervertebral disc degeneration and proteoglycan content in cadaveric human lumbar spine tissue.

Objective: To show the use of T1rho-weighted magnetic resonance imaging (MRI) for the assessment of degeneration and proteoglycan content in the human intervertebral disc.

Summary of background data: Loss of proteoglycan in the nucleus pulposus occurs during early degeneration. Conventional MRI techniques cannot detect these early changes in the extracellular matrix content of the disc. T1rho MRI is sensitive to changes in proteoglycan content of articular cartilage and may, therefore, be sensitive to proteoglycan content in the intervertebral disc.

Methods: Intact human cadaveric lumbar spines were imaged on a clinical MR scanner. Average T1rho in the nucleus pulposus was calculated from quantitative T1rho maps. After MRI, the spines were dissected, and proteoglycan content of the nucleus pulposus was measured. Finally, the stage of degeneration was graded using conventional T2 images.

Results: T1rho decreased linearly with increasing degeneration (r = -0.76, P < 0.01) and age (r = -0.76, P < 0.01). Biochemical analysis revealed a strong linear correlation between T1rho and sulfated-glycosaminoglycan content. T1rho was moderately correlated with water content.

Conclusions: Results from this study suggest that T1rho may provide a tool for the diagnosis of early degenerative changes in the disc. T1rho-weighted MRI is a noninvasive technique that may provide higher dynamic range than T2 and does not require a high static field or exogenous contrast agents.

Figure 1

Representative T_1ρ-weighted images (Left) and quantitative T_1ρ maps (Right) for 2 lumbar spine sections. Each pixel in the maps represents the quantitative measurement of T_1ρ at that spatial location. Age 25, average degenerative grade 1.25 (Top). Age 51, average degenerative grade 2.25 (Bottom).

Figure 2

Correlation between T_1ρ values and degenerative grade.

Figure 3

A, Correlation between T_1ρ and sulfated-glycosaminoglycan/wet weight (B) T_1ρ and sulfated-glycosaminoglycan/dry weight (C) T_1ρ and water content, and age (D).

Figure 4

Spin-lock MRI techniques, such as T_1ρ-weighted imaging, may detect degenerative changes earlier than conventional MRI or radiography.