Characteristics of proton NMR T-2 relaxation of water in the normal and regenerating tendon

The molecular behavior of water in normal and regenerating tendons was anal yzed using the transverse relaxation time (T-2) measured by spin-echo proto n nuclear magnetic resonance (H-1-NMR) spectroscopy at 2.34 T (25 degreesC) . A section of the Achilles tendon was dissected from an anesthetized Japan ese white rabbit, and its longitudinal axis was oriented at 0, 35, 54.7, 75 , and 90 degrees to the static magnetic field. In the normal tendon, the T- 2 relaxation of water presented biexponential relaxation and anisotropy in both the long T-2 (5.41 to 6.21 ms) and short T-2 (0.41 to 1.43ms) componen ts, in which the greatest values were obtained at 54.7 degrees. However, th e range of the anisotropy was much narrower than we expected from the H-1 d ipolar interaction of water bound to the collagen fibers in the tendon. The apparent fractions of water proton density also varied with orientation: t he fraction of the longer T-2 components was at its maximum at 54.7 degrees . These results suggest that a simple two-compartment model could not be ap plicable to orientational dependency of the T-2 value of the tendon, and th e well ordered water in the short T-2 relaxation component may show an elon gated T-2 relaxation time that falls in the range of the long T-2 relaxatio n component at 54.7 degrees. This hypothesis can explain both the narrower range of the T-2 relaxation time and the orientational dependency on the ap parent fraction of H-1 density. Regenerating processes of the Achilles tend on were followed for 18 weeks by analyzing the T-2 relaxation time. There i s only a long T-2 relaxation time component (21.8 to 28.0 ms) up to 3 weeks after transection. Biexponential relaxation is revealed at 6 weeks and the reafter, whereby (i) the T-2 relaxation times become shorter, (ii) there is anisotropy in the short and long T-2 values, and (iii) the orientational d ependency of the apparent fraction of water proton density becomes evident with maturation of the regenerating tendon. From these results, the H-1 T-2 relaxation time of water might be used to monitor the healing process of c ollagen structures of the tendon non-invasively.