Knee MRI with in-situ mechanical loading using prospective motion correction
Osteoarthritis of the knee joint is often caused by excessive or inadequate mechanical loading. Therefore knee cartilage response to exercise paradigms involving knee loading such as running or squatting has been the focus of recent MRI research. However, to date there are only a few studies that have been performed with in situ loading, mainly because such experiments are strongly hampered by load-induced subject motion. Motion artifacts are particularly severe for loading of the patellofemoral joint, which requires knee flexion. In our group, we develop knee MRI techniques with in-situ mechanical loading using prospective motion correction based on optical tracking. In-situ knee loading is realized with an MR-compatible pneumatic loading jig enabling accurate load adjustment in the range 0–50 kg. Prospective motion correction is performed with a moiré phase tracking (MPT) system (Metria Innovation Inc., Milwaukee, US) consisting of a single in-bore camera and a tracking marker, which is taped to the knee cap. We could demonstrate a considerable improvement of image quality, yielding high-resolution knee images appropriate for measuring the load-induced cartilage deformation. Furthermore, we investigate load-induced relaxation changes of articular cartilage with this technique.