Characteristics of Proton NMR T_2 Relaxation of Water in the Normal and Regenerating Tendon

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The molecular behavior of water in normal and regenerating tendons was analyzed using the transverse relaxation time (T<sub>2</sub>) measured by spin-echo proton nuclear magnetic resonance (<sup>1</sup>H-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 T<sub>2</sub> relaxation of water presented biexponential relaxation and anisotropy in both the long T<sub>2</sub> (5.41 to 6.21 ms) and short T<sub>2</sub> (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 <sup>1</sup>H 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 T<sub>2</sub> 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 T<sub>2</sub> value of the tendon, and the well ordered water in the short T<sub>2</sub> relaxation component may show an elongated T<sub>2</sub> relaxation time that falls in the range of the long T<sub>2</sub> relaxation component at 54.7°. This hypothesis can explain both the narrower range of the T<sub>2</sub> relaxation time and the orientational dependency on the apparent fraction of <sup>1</sup>H density. Regenerating processes of the Achilles tendon were followed for 18 weeks by analyzing the T<sub>2</sub> relaxation time. There is only a long T<sub>2</sub> 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 T<sub>2</sub> relaxation times become shorter, (ii) there is anisotropy in the short and long T<sub>2</sub> 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 <sup>1</sup>H T<sub>2</sub> relaxation time of water might be used to monitor the healing process of collagen structures of the tendon non-invasively.<br>


  • The Japanese Journal of Physiology

    The Japanese Journal of Physiology 50(6), 569-576, 2000-12-01


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