Relaxation anisotropy in cartilage by NMR microscopy (μMRI) at 14-μm resolution

TLDR: The result suggests that the interactions between water molecules and proteoglycans have a directional nature, which is somehow influenced by collagen fibril orientation, and T2 anisotropy could serve as a sensitive and noninvasive marker for molecular‐level orientations in articular cartilage.

Abstract: To study the structural anisotropy and the magic-angle effect in articular cartilage, T 1 and T 2 images were constructed at a series of orientations of cartilage specimens in the magnetic field by using NMR microscopy (μMRI). An isotropic T 1 and a strong anisotropic T 2 were observed across the cartilage tissue thickness. Three distinct regions in the microscopic MR images corresponded approximately to the superficial, transitional, and radial histological zones in the cartilage. The percentage decrease of T 2 follows the pattern of the curve of (3cos 2 θ - 1) 2 at the radial zone, where the collagen fibrils are perpendicular to the articular surface. In contrast, little orientational dependence of T 2 was observed at the transitional zone, where the collagen fibrils are more randomly oriented. The result suggests that the interactions between water molecules and proteoglycans have a directional nature, which is somehow influenced by collagen fibril orientation. Hence, T 2 anisotropy could serve as a sensitive and noninvasive marker for molecular-level orientations in articular cartilage.