The past decade has seen tremendous growth in efforts to establish noninvasive assessments of articular cartilage, motivated by a need to evaluate the efficacy of therapeutic interventions and to understand disease progression. The main tool in this regard is magnetic resonance imaging (MRI), which has emerged as the preferred means of imaging cartilage anatomy, and underlies the developing methods for imaging cartilage biochemical properties. Though anatomy and biochemistry of cartilage are undeniably important metrics, the sine qua non of cartilage functional integrity is its mechanical properties. The hypothesis to be examined in this proposal is that a spatial map computed from a combination MRI-derived biochemical metrics will correspond to spatially-localized mechanical properties. Preliminary studies using three human tibial plateau samples showed a strong correlation between a spatial map of GAG concentration (measured by MRI) and a corresponding map of mechanical stiffness (measured by indentation studies), suggesting the potential for MRI to provide a noninvasive measure of the cartilage mechanical properties. To build on these exciting preliminary data we aim to: 1. Evaluate whether the correlation between GAG and arthroscopic-probe indentation behavior is sustained as sample number is increased and whether the correlation is improved by considering an additional an MRI measure (T2) known to be influenced by collagen. 2. Evaluate the three regimes of mechanical behavior to see whether they have the same dependency on the biochemically-based MR metrics. The proposed studies represent an essential and new step towards functional imaging of cartilage. Importantly, the relatively new MR methodologies that reflect tissue biochemical properties provide the enabling technology that opens up this avenue of research. The spatially-localized information provided here would be potentially valuable in a myriad of contexts ranging from aiding our basic understanding of the macromolecular mechanism conferring cartilage stiffness, to the practical clinical question of identifying whether tissue is functionally competent.
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