The effects of mechanical loading and gadolinium concentration on the change of T1 and quantification of glycosaminoglycans in articular cartilage by microscopic MRI.

Microscopic MRI (µMRI) T1 experiments were carried out to investigate the strain dependence of the T1 change and glycosaminoglycans (GAG) quantification in articular cartilage at a spatial resolution of 17.6 µm. Both native and trypsin-degraded specimens were immersed in various concentrations of gadolinium (Gd) (up to 1 mM) and imaged at different strains (up to 50% strains). Adjacent specimens were treated identically and analyzed biochemically by an inductively coupled plasma optical emission spectrometer. The T1 profile in the native tissue was found to be both strain-dependent and depth-dependent, while there was no obvious depth-dependence in the degraded tissue. For the native tissue, compression reduced the tissue T1 when Gd in the solution was low (less than 0.4 mM) and increased the tissue T1 when Gd in the solution was high. A set of critical points, where the tissue T1 showed no change at a certain Gd concentration between two different loadings, was observed for the first time in the native tissue. It is concluded that the GAG quantification by MRI was accurate as long as the Gd concentration in the solution reached at least 0.2 mM (tissue not loaded) or 0.4 mM (tissue loaded).