Modifications of orientational dependence of microscopic magnetic resonance imaging T2 anisotropy in compressed articular cartilage

Purpose: To investigate the compression-induced changes in the orientational characteristics in T-2 anisotropy of articular cartilage using microscopic magnetic resonance imaging (mu MRI). Materials and Methods: Six beagle specimens were subjected to various levels of strain (0% to 27%) and were imaged at a minimum of two orientations (0 degrees and 55 degrees). Two specimens at 14% and 27% strain were imaged at every 5 degrees increment over the first quadrant of the angular space. Quantitative two-dimensional T-2 images and three-dimensional T-2 anisotropy maps of cartilage were constructed at a 19.8-mu m in-depth resolution. Results: The load-induced laminar appearance of cartilage at the magic angle became more distinct as the strain level increased. T-2 anisotropy maps of cartilage at 14% and 27% strain exhibited load-induced modifications in the collagen fibril ultrastructure, with a new peak toward the cartilage-bone inter-face and alterations to orientational dependence of T-2 anisotropy. Conclusion: Distinct alternations in the orientational dependence of mu MRI T-2 anisotropy reflect the organizational modification of the collagen matrix due to external loading. This approach could become useful in detecting changes in cartilage's macromolecular structure due to injury or diseases.