ORIGIN OF CARTILAGE LAMINAE IN MRI

To understand the origin of the laminated appearance of cartilage in M RI (the magic angle effect), microscopic MRL (mu MRI) experiments were performed at 14-mu m pixel resolution on normal canine articular cart ilage from the shoulder joints, Two-dimensional images of the spin-spi n relaxation time (T2) of the cartilage-bone plug at two angles (0 deg rees and 55 degrees) were calculated quantitatively, A distinct T2 ani sotropy was observed as a function of the cartilage tissue depth. The surface and the deep regions exhibit strong orientational dependence o f T2, whereas the upper-middle region exhibits little orientational de pendence of T2. These three mu MRI regions correspond approximately to the three histologic zones in cartilage tissue. The results from the bulk T2 measurements agreed with these mu MRI results, Our studies sho w that the laminated appearance of cartilage in MRI is caused by T2 an isotropy of the tissue. We further suggest that the molecular origin o f the T2 anisotropy is the nuclear dipolar interaction. The structure of the cartilage tissue indicates that the collagen meshwork defines t his T2 anisotropy. The results show that the T2 anisotropy provides an indirect but sensitive indicator for the orientation of macromolecula r structures in cartilage. The clinical implications of this anisotrop y are discussed.