Clinical applications of UTE-T2* in knee MRI

Many of the tissues of interest in the evaluation of the knee by magnetic resonance imaging (MRI), including subchondral bone, deep calcified layer of cartilage, menisci, tendons, and ligaments, have very short transverse (T2 and T2*) relaxation times related to their intrinsic structure. These tissues appear anechoic on conventional MRI sequences as signal has already decayed to its minimum when image acquisition begins. Only in the setting of significant injury or degeneration is there detectable signal on conventional MRI sequences. Ultrashort echo time (UTE) MRI, which allows for the qualitative and quantitative assessment of short T2 tissues in their normal states, offers a unique opportunity to detect and intervene upon pathological changes early to prevent irreversible damage. Changes on UTE-T2* imaging allow for the identification of subtle alterations in collagen structure, hydration status, and mineralization of tissues that precede morphologic changes visible on conventional imaging. Early detection of such microstructural changes can allow for the earlier diagnosis of tendinopathy, meniscal injury or degeneration, and early osteoarthritis, potentially allowing for improved patient outcomes through earlier intervention. This review will focus specifically on the clinical applications of one UTE MRI technique, UTE-T2*, in the evaluation of musculoskeletal tissues about the knee.