Imaging of nuclear magnetic resonance spin–lattice relaxation activation energy in cartilage

Samples of human and bovine cartilage have been examined using magnetic resonance imaging to determine the proton nuclear magnetic resonance spin–lattice relaxation time, T 1 , as a function of depth within through the cartilage tissue. T 1 was measured at five to seven temperatures between 8 and 38°C. From this, it is shown that the T 1 relaxation time is well described by Arrhenius-type behaviour and the activation energy of the relaxation process is quantified. The activation energy within the cartilage is approximately 11 ± 2 kJ mol −1 with this notably being less than that for both pure water (16.6 ± 0.4 kJ mol −1 ) and the phosphate-buffered solution in which the cartilage was immersed (14.7 ± 1.0 kJ mol −1 ). It is shown that this activation energy increases as a function of depth in the cartilage. It is known that cartilage composition varies with depth, and hence, these results have been interpreted in terms of the structure within the cartilage tissue and the association of the water with the macromolecular constituents of the cartilage.