Comparative study of the sensitivity of ADC value and T₂ relaxation time for early detection of Wallerian degeneration.

Background And Purpose: Wallerian degeneration (WD), the secondary degeneration of axons from cortical and subcortical injuries, is associated with poor neurological outcome. There is some quantitative MR imaging techniques used to estimate the biologic changes secondary to delayed neuronal and axonal losses. Our purpose is to assess the sensitivity of ADC value and T(2) relaxation time for early detection of WD.

Methods: Ten male Sprague-Dawley rats were used to establish in vivo Wallerian degeneration model of CNS by ipsilateral motor-sensory cortex ablation. 5 days after cortex ablation, multiecho-T(2) relaxometry and multi-b value DWI were acquired by using a 7T MR imaging scanner. ADC-map and T(2)-map were reconstructed by post-processing. ROIs are selected according to pathway of corticospinal tract from cortex, internal capsule, cerebral peduncle, pons, medulla oblongata to upper cervical spinal cord to measure ADC value and T(2) relaxation time of healthy side and affected side. The results were compared between the side with cortical ablation and the side without ablation.

Results: Excluding ablated cortex, ADC values of the corticospinal tract were significantly increased (P<0.05) in affected side compared to the unaffected, healthy side; no difference in T(2) relaxation time was observed between the affected and healthy sides. Imaging findings were correlated with histological examinations.

Conclusion: As shown in this animal experiment, ADC values could non-invasively demonstrate the secondary degeneration involving descending white matter tracts. ADC values are more sensitive indicators for detection of early WD than T(2) relaxation time.