Cross-relaxation imaging of human articular cartilage.

In this article, cross-relaxation imaging is applied to human ex vivo knee cartilage, and correlations of the cross-relaxation imaging parameters with macromolecular content in articular cartilage are reported. We show that, unlike the more commonly used magnetization transfer ratio, the bound pool fraction, the cross-relaxation rate (k) and the longitudinal relaxation time (T(1)) vary with depth and can therefore provide insight into the differences between the top and bottom layers of articular cartilage. Our cross-relaxation imaging model is more sensitive to macromolecular content in the top layers of cartilage, with bound pool fraction showing moderate correlations with proteoglycan content, and k and T(1) exhibiting moderate correlations with collagen.