The zonal architecture of human articular cartilage described by T2 relaxation time in the presence of Gd-DTPA2−

The depth-wise variation of T2 relaxation time is known to reflect the collagen network architecture in cartilage, while the delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) technique is sensitive to tissue proteoglycan (PG) concentration. As the cartilage PG content varies along the tissue depth, the depth-dependent accumulation of the contrast agent may affect the inherent T2 of cartilage in a nonconstant manner. Therefore, T2 and dGEMRIC are typically measured in separate MRI sessions. In the present in vitro MRI study at 9.4 T, depth-wise T2 profiles and collagenous zone thicknesses as determined from T2 maps in the absence and presence of Gd-DTPA2− (T2 and T2Gd, respectively) were compared in samples of intact human articular cartilage (n=65). These T2 measures were further correlated with birefringence (BF) of polarized light microscopy (PLM) to quantify the ability of MRI to predict the properties of the collagen fibril network. The reproducibility of the T2 measurement in the current setup was also studied. Typical tri-laminar collagen network architecture was observed both with and without Gd-DTPA2−. The inverse of BF (1/BF) correlated significantly with both T2 and T2Gd (r=0.91, slope=0.56 and r=0.90, slope=0.63), respectively. The statistically significant linear correlations between zone thicknesses as determined from T2 and T2Gd were r=0.55 (slope=0.49), r=0.74 (slope=0.71) and r=0.95 (slope=0.94) for superficial, middle and deep tissue zones, respectively. Reproducibility of the T2 measurement was worst for superficial cartilage. Consistent with PLM, T2 and T2Gd measurements reveal highly similar depth-dependent information on collagen network in intact human cartilage. Thus, dGEMRIC and T2 measurements in one MRI session are feasible for intact articular cartilage in vitro.