The influence of collagen network integrity on the accumulation of gadolinium-based MR contrast agents in articular cartilage

Delayed gadolinium-enhanced MR imaging of cartilage is used to quantify the proteoglycan loss in early osteoarthritis. It is assumed that T 1 after Gd-DTPA administration in the near equilibrium state reflects selective proteoglycan loss from cartilage. To investigate the influence of the collagen network integrity on contrast accumulation, the relaxation rates ΔR1 and ΔR2 were compared after Gd-DTPA administration in a well established model of osteoarthritis. Collagen or proteoglycan depletion was induced by the proteolytic enzymes papain and collagenase in healthy bovine patellar cartilage. Using a dedicated MRI sequence, T1 and T2 maps were simultaneously acquired before and 11 h after Gd-DTPA administration. Depth-dependent profiles of ΔR1 and ΔR2 were calculated in healthy, proteoglycan and collagen-depleted articular cartilage and the mean values of different cartilage layers were compared using the Mann-Whitney-U test. In superficial layers (1 mm) there was no significant difference (p > 0.05) in either ΔR1 or ΔR2 between proteoglycan-depleted (16.6 ± 1.2 s-1, 15.9 ± 1.0 s-1) and collagen-depleted articular cartilage (15.3 ± 0.9 s-1, 15.5 ± 0.9 s-1). In deep layers (3 mm) both parameters were significantly higher (p = 0.005, 0.03) in proteoglycan-depleted articular cartilage (12.3 ± 1.1 s-1, 9.8 ± 0.8 s-1) than in collagen-depleted articular cartilage (9.1 ± 1.1 s-1, 8.7 ± 0.7 s-1). Both proteoglycan loss and alterations in the collagen network influence the accumulation of Gd-DTPA in articular cartilage with significant differences between superficial and deep cartilage layers. (orig.)