Assessing degeneration of human articular cartilage with ultra-short echo time (UTE) T2 mapping

Summary Objective To examine the sensitivity of ultra-short echo time (UTE) T2 * mapping to collagen matrix degeneration in human articular cartilage. Methods Magnetic resonance imaging (MRI) UTE- T2 * maps and standard T2 maps were acquired on four human tibial plateau explants. Thirty-three osteochondral cores were harvested for polarized light microscopy (PLM), and composition analyses. Collagen matrix integrity was evaluated from PLM and histological images. Matrix integrity and composition was compared to standard T2 values and UTE- T2 * values on a spatially registered basis. Results UTE- T2 * values varied with matrix degeneration ( P = 0.008) and were lower in severely degraded cartilage compared to healthy tissue ( P = 0.012). A trend for higher UTE- T2 * values in healthy tissue compared to mildly degenerate tissue ( P = 0.051) was detected. Standard T2 values were not found to vary with matrix degeneration ( P = 0.13) but tended to be higher in severely degraded cartilage compared to healthy tissue. UTE- T2 * value variations were independent of type-II collagen and glycosaminoglycan contents. UTE- T2 * mapping of deep cartilage, adjacent to subchondral bone, was more robust than standard T2 mapping in this zone. Conclusion UTE- T2 * mapping of articular cartilage is sensitive to matrix degeneration and detects short- T2 signal, particularly in deep tissue, that is not well captured by standard T2 mapping. Correlation of UTE- T2 * values and PLM indices supports the hypothesis that both may be sensitive to collagen microstructure. Further exploration of UTE- T2 * mapping as a non-invasive tool to detect early articular cartilage degeneration is warranted.