A Noninvasive MRI-Based Method to Determine Three Dimensional Cartilage Deformations

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Articular cartilage is critical to the normal function of human diarthrodial joints. The tissue has unique mechanical and tribological properties which allow for daily activities (i.e. locomotion) by providing a nearly frictionless and wear-resistant joint surface. Osteoarthritis is the most common rheumatic disease and is associated with various degrees of cartilage degradation. Despite the unique function of normal cartilage and the prevalence of osteoarthritis, previous studies have not quantified the three-dimensional (3D) mechanical deformation of cartilage using noninvasive experimental methods. The lack of such comprehensive information regarding cartilage deformations seriously limits our understanding of normal cartilage load-deformation behavior and hence our ability to completely describe, accurately diagnose, and effectively treat cartilage disorders. Thus the goal of this research is to develop a method to noninvasively determine the 3D deformation of cartilage.To meet this goal, three hypotheses will be tested as follows: (1) a noninvasive magnetic resonance imaging (MRI) pulse sequence can be designed to directly observe cartilage deformation at high spatial resolution of 50 microns, (2) deformation can be measured using the new noninvasive method with less than 5% relative error in strain, and (3) 3D cartilage deformation in osteoarthritic cartilage samples is altered from deformation in normal samples. To test the first hypothesis, tissue deformation will be observed using a specific MRI pulse sequence that superimposes a grid pattern on the cartilage which can be observed to move with the tissue as it deforms. To test the second hypothesis, the accuracy of the noninvasive method will be determined using a MRI-compatible phantom. The 3D finite strain tensor field will be computed from high-resolution MRI images from samples of normal and osteoarthritic tissues to test the third hypothesis. The development of the new noninvasive method is motivated by many basic science and clinical research questions. Once the method is proven by testing the above hypotheses, it will permit noninvasive investigation of the effects of gender, age, degeneration, treatment, repair and healing on cartilage load-deformation. This research represents the foundation of a long-term research program which aims to increase our understanding of normal and abnormal 3D cartilage deformations in vivo.