Strain‐dependent T1 relaxation profiles in articular cartilage by MRI at microscopic resolutions

To investigate the dependency of T₁ relaxation on mechanical strain in articular cartilage, quantitative magnetic resonance T₁ imaging experiments were carried out on cartilage before/after the tissue was immersed in gadolinium contrast agent and when the tissue was being compressed (up to ～48% strains). The spatial resolution across the cartilage depth was 17.6 μm. The T₁ profile in native tissue (without the presence of gadolinium ions) was strongly strain‐dependent, which is also depth‐dependent. At the modest strains (e.g., 14% strain), T₁ reduced by up to 68% in the most surface portion of the tissue. Further compression (e.g., 45% strain) reduced T₁ mostly in the middle and deep portions of the tissue. For the gadolinium‐immersed tissue, both modest and heavy compressions (up to 48% strain) increased T₁ slightly but significantly, although the overall shapes of the T₁ profiles remained approximately the same regardless of the amount of strains. The complex relationships between the T₁ profiles and the mechanical strains were a direct consequence of the depth‐dependent proteoglycan concentration in the tissue, which determined the tissue's mechanical properties. This finding has potential implications in the use of gadolinium contrast agent in clinical magnetic resonance imaging of cartilage (the dGEMRIC procedure), when the loading or loading history of patients is considered. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.