Multicomponent T 2 * mapping of knee cartilage: Technical feasibility ex vivo

Disorganization of collagen fibers is a sign of early‐stage cartilage degeneration in osteoarthritic knees. Water molecules trapped within well‐organized collagen fibrils would be sensitive to collagen alterations. Multicomponent effective transverse relaxation ( T 2 *) mapping with ultrashort echo time acquisitions is here proposed to probe short T 2 relaxations in those trapped water molecules. Six human tibial plateau explants were scanned on a 3T MRI scanner using a home‐developed ultrashort echo time sequence with echo times optimized via Monte Carlo simulations. Time constants and component intensities of T 2 * decays were calculated at individual pixels, using the nonnegative least squares algorithm. Four T 2 *‐decay types were found: 99% of cartilage pixels having mono‐, bi‐, or nonexponential decay, and 1% showing triexponential decay. Short T 2 * was mainly in 1‐6 ms, while long T 2 * was ∼22 ms. A map of decay types presented spatial distribution of these T 2 * decays. These results showed the technical feasibility of multicomponent T 2 * mapping on human knee cartilage explants. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.