Disorganization of collagen fibers is a sign of early-stage cartilage degeneration in osteoarthritis knees. Water molecules trapped within well-organized collagen fibrils would be sensitive to collagen alterations. Multi-component T2* mapping with ultrashort echo time (UTE) acquisitions is here proposed to probe short T2 relaxations in those trapped water molecules. Six human tibial plateau explants were scanned on a 3T MRI scanner using a home-developed UTE sequence with TEs optimized via Monte Carlo simulations. Time constants and component intensities of T2* decays were calculated at individual pixels using the nonnegative least squares algorithm. Four T2*-decay types were found: 99% of cartilage pixels having mono-, bi-, or non-exponential decay, and 1% showing tri-exponential decay. Short T2* was mainly in 1-6ms while long T2* was ~22ms. A map of decay types presented spatial distribution of these T2* decays. These results showed the technical feasibility of multi-component T2* mapping on human knee cartilage explants.
展开▼
