Evaluation of radiation‐induced peripheral nerve injury in rabbits with MR neurography using diffusion tensor imaging and T 2 measurements: Correlation with histological and functional changes

Purpose To investigate the potential of diffusion tensor imaging (DTI) and T 2 measurements in the evaluation of radiation‐induced peripheral nerve injury (RIPNI). Materials and Methods RIPNI was produced in a randomly selected side of sciatic nerve in each of 21 rabbits while the contralateral side served as the control. The limb function and MR parameters were evaluated over a 4‐month period. Fractional anisotropy (FA), axial diffusivity (λ ∥ ), radial diffusivity (λ ⊥ ) and T 2 values were obtained using 3T MR for quantitative analysis. Two animals were randomly killed for histological evaluation at each timepoint. Results The T 2 value of irradiated nerve increased at 1 day (63.95 ± 15.60, P = 0.012) and was restored at 1 month (52.34 ± 5.38, P = 0.105). It increased progressively at 2 to 4 months (60.39 ± 10.60, 66.96 ± 6.08, 75.51 ± 7.39, all P < 0.01). λ ⊥ significantly increased at 1 day (0.82 ± 0.44, P = 0.046) and slightly decreased at 1 month (0.61 ± 0.17, P < 0.001). It increased gradually from 2 to 3 months (0.84 ± 0.29, 1.13 ± 0.33, both P < 0.001) followed by a decline at 4 months (0.83 ± 0.17, P < 0.001). FA was statistically lower than the contralateral sides at 1 to 4 months (0.72 ± 0.08, 0.60 ± 0.12, 0.51 ± 0.11, 0.62 ± 0.06, all P < 0.01). Changes in FA and λ ⊥ correlated well with the functional and pathological changes in irradiated nerve. Conclusion DTI may be a more sensitive and accurate method to evaluate RIPNI compared with T 2 measurements. FA and λ ⊥ are promising quantitative indices in monitoring RIPNI. J. Magn. Reson. Imaging 2016;43:1492–1499.