2000 Volume 50 Issue 6 Pages 569-576
The molecular behavior of water in normal and regenerating tendons was analyzed using the transverse relaxation time (T2) measured by spin-echo proton nuclear magnetic resonance (1H-NMR) spectroscopy at 2.34 T (25°C). A section of the Achilles tendon was dissected from an anesthetized Japanese white rabbit, and its longitudinal axis was oriented at 0, 35, 54.7, 75, and 90° to the static magnetic field. In the normal tendon, the T2 relaxation of water presented biexponential relaxation and anisotropy in both the long T2 (5.41 to 6.21 ms) and short T2 (0.41 to 1.43 ms) components, in which the greatest values were obtained at 54.7°. However, the range of the anisotropy was much narrower than we expected from the 1H dipolar interaction of water bound to the collagen fibers in the tendon. The apparent fractions of water proton density also varied with orientation: the fraction of the longer T2 components was at its maximum at 54.7°. These results suggest that a simple two-compartment model could not be applicable to orientational dependency of the T2 value of the tendon, and the well ordered water in the short T2 relaxation component may show an elongated T2 relaxation time that falls in the range of the long T2 relaxation component at 54.7°. This hypothesis can explain both the narrower range of the T2 relaxation time and the orientational dependency on the apparent fraction of 1H density. Regenerating processes of the Achilles tendon were followed for 18 weeks by analyzing the T2 relaxation time. There is only a long T2 relaxation time component (21.8 to 28.0 ms) up to 3 weeks after transection. Biexponential relaxation is revealed at 6 weeks and thereafter, whereby (i) the T2 relaxation times become shorter, (ii) there is anisotropy in the short and long T2 values, and (iii) the orientational dependency of the apparent fraction of water proton density becomes evident with maturation of the regenerating tendon. From these results, the 1H T2 relaxation time of water might be used to monitor the healing process of collagen structures of the tendon non-invasively.
