Abstract
OBJECTIVE: To develop and characterize the MR properties of a synthetic model for cartilage extra-cellular matrix using hydrogels and to determine the concentration dependence of spin-lattice (T1) and spin-spin (T2) relaxation times of hydrogels and their glycosaminoglycan and collagen components in the presence and absence of gadopentetate dimeglumine (Gd-DTPA) for use in dGEMRIC. MATERIALS AND METHODS: T1 and T2 measurements were made at 3 Tesla on a range of gelatin (i.e., collagen) and hyaluronan (i.e., glycosaminoglycan) solutions (6.25-100 g/l), alone, together in a composite, and as dityramine-bridged hydrogels. Relaxivity was calculated as a function of macromolecular concentration. RESULTS: Even at the highest concentrations, gelatin and hyaluronan solutions had T1 and T2 values significantly larger than those reported for cartilage. Only composite hydrogels with gelatin and hyaluronan concentrations naturally found in cartilage resulted in T1 values, but not T2 values, representative of cartilage. Relaxivities were slightly dependent on both hyaluronan concentration (R1 = 0.0027 l g(-1) s(-1); R2 = 0.025 l g(-1) s(-1)) and gelatin concentration (R1 = 0.0032 l g(-1) s(-1); R2 = 0.020 l g(-1) s(-1)) alone and as a composite (R1 = 0.0068 l g(-1) s(-1); R2 = 0.101 l g(-1) s(-1)). Gd-DTPA relaxivities were dependent upon macromolecular concentration and varied by 14-32% (R1 = 4.24 to 5.55 mM(-1) s(-1); R2 = 4.60 to 6.27 mM(-1) s(-1)) over the range of cartilage biochemistry. CONCLUSIONS: Without the contrast agent, hyaluronan and gelatin, alone or in a composite, have a very small impact on the relaxivities of the model system. The impact on R1 was approximately tenfold less than on R2. In contrast, macromolecular concentrations above 50 g/l significantly impacted Gd-DTPA relaxivity and should be accounted for when measuring the glycosaminoglycan content of cartilage in vivo using dGEMRIC.