MR Characterization of Human Cartilage Degeneration using T1rho and DTI

Osteoarthritis, an irreversible disease of cartilage degeneration, has become a global socioeconomic burden. Consequently, there is a strong desire to diagnose the early degeneration of the cartilage so that increasing efforts can be made to develop the effective disease-modifying therapies. Comparing with other radiography, MRI can give not only the morphologic features but also quantitative information from the relaxation time and diffusion coefficient. Microscopic MRI has the advantage to get the high resolution image and distinguish the different zones of the cartilage.;The loss of the proteoglycans and the cleavage of the collagens are two major features during the cartilage degeneration. Conventional T1 and T2 relaxations in MRI have been proven to be inadequate in quantifying the early-stage molecular changes, while T1rho and Diffusion tensor imaging (DTI) are two potential methods to detect the PG loss and the collagen cleavage.;T1rho has the advantage to generate quantitative information about low-frequency physico-chemical interactions between bulk water and surrounding molecules in biological tissue. By using the spin-lock technique, T1rho experiments can be performed at the 11.7 T high magnetic field to provide information about low frequency motions (∼few kHz) in biological systems with high SNR. In the first study, T1rho measurements in three zones of normal and degenerated cartilage have shown the strong relation between the change of T1rho value and the loss of Proteoglycans.;DTI has been used to analyze the microstructure of human cartilages. Previous literatures showed low range of fractional anisotropy (FA: 0.1∼0.3) in the cartilage, especially low FA (≤ 0.1) in the superficial zone. In the second study, after using the long diffusion time, FA values of each zone in the grade 0 cartilages were consistent with the collagen anisotropy. In the superficial zone, FA of grade 1 cartilages were significantly lower than FA of grade 0 cartilages and thus improved the sensitivity to detect the damage of collagens in the early stage of cartilage degeneration.;In view of current efforts, both techniques used in T1rho and DTI experiments have contributed to detecting the early degeneration of the human cartilages.