Evaluation of radiation-induced peripheral nerve injury in rabbits with MR neurography using diffusion tensor imaging and T2 measurements: Correlation with histological and functional changes

Abstract

Purpose To investigate the potential of diffusion tensor imaging (DTI) and T2 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 (λâ), radial diffusivity (λâ) and T2 values were obtained using 3T MR for quantitative analysis. Two animals were randomly killed for histological evaluation at each timepoint. Results The T2 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). λâ 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 λâ 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 T2 measurements. FA and λâ are promising quantitative indices in monitoring RIPNI.