Textural Features from Quantitative MRI Using T2 Relaxation Times Correlate with Histological Cartilage Degeneration: An Ex-Vivo Study

Objective To assess the relationship between textural features derived from quantitative MRI (T 2 mapping) and histological signs of cartilage degeneration. Design Ten fresh non-frozen knees from body donors were measured at 7T and 3T scanners using 3D-Double Echo Steady State (3D-DESS) as well as 3D-Triple Echo Steady State (3D-TESS) sequence. The 3D-DESS images were automatically segmented and co-registered with T 2 maps at both field strengths. Nine osteochondral plugs were harvested from standardized regions of the distal femur of each knee. The histological workup included Safranin O and picrosirius red staining. Mankin scoring was performed for each plug. Collagen orientation and parallelism were assessed and quantified based on polarized light microscopy. Each plug was segmented on the 3D model derived from 3D-DESS image and texture analysis was performed on the co-registered T 2 map. Relationships between T 2 relaxation time, textural features and the Mankin score, as well as collagen orientation and parallelism, were assessed using partial Spearman’s correlation coefficients and mixed models. Results Mean T 2 and six features (autocorrelation, contrast, correlation, entropy, sum entropy and inverse difference moment normalized) correlated with the MS; autocorrelation, contrast and entropy were also found to be correlated with collagen orientation. No features were significantly correlated with parallelism. Statistical models showed no significant effect of sequence or field strength in predicting Mankin score. Conclusions The presented ex-vivo approach enables a semi-automated assessment of articular cartilage quality that correlates with histological measures of degeneration. Additional studies are warranted to further investigate the reproducibility and validity of the measurements.