Spatial gradient in vertebral–disc coupling: independent associations of bone marrow fat fraction and perfusion with disc biochemistry

To evaluate the relationship between vertebral bone marrow fat, blood flow perfusion, and IVD biochemical components in postmenopausal women using quantitative MRI. Postmenopausal women were categorized into three groups based on QCT: normal BMD (n = 34), osteopenia (n = 27), and osteoporosis (n = 24). Lumbar vertebral bone marrow fat fraction (FF) was quantified using a 6-echo-based Dixon sequence. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) provided quantitative parameters for bone marrow blood perfusion (Ktrans, Kep, Ve). T2 mapping imaging assessed lumbar disc degeneration, yielding T2 values for the nucleus pulposus (NP), anterior annulus fibrosus (AAF), and posterior annulus fibrosus (PAF). We analyzed Spearman correlation coefficients and identified independent factors influencing disc T2 values through multiple linear regression analysis. Significant differences were found in FF, Ktrans, Kep, and Ve values across groups (p < 0.001, p < 0.001, p < 0.001, p = 0.025). FF showed a strong inverse correlation with adjacent NP T2 values at L1 (r = -0.760, adjusted p < 0.001), and moderate at L2 and L3 (r = -0.613, adjusted p < 0.001; r = -0.455, adjusted p < 0.001). Positive correlations were found between Ktrans and adjacent NP T2 values at all levels (r = 0.715 to 0.314, adjusted p < 0.01 to < 0.001). A multivariate linear regression analysis revealed that FF and Ktrans values were independent predictors of adjacent NP T2 values at L1 to L4 levels. Both vertebral bone marrow FF and Ktrans are independent predictors of intervertebral disc health, as reflected by nucleus pulposus T2 values. Notably, these relationships exhibit a distinct craniocaudal gradient, with stronger vertebral-disc coupling in the upper lumbar spine. Multiparametric quantitative MRI provides deeper insights into early disc degeneration pathways beyond single-parameter assessments.