Diffusion Tensor Imaging of Epilepsy

  • Author / Creator
    Liu, Min
  • Temporal lobe epilepsy (TLE) and idiopathic generalized epilepsy (IGE) are two common epilepsy syndromes. TLE is a type of focal epilepsy. It is frequently associated with mesial temporal sclerosis (MTS), a condition that is also medically intractable. Although TLE is characterized by a focal lesion, widespread gray matter (GM) and white matter (WM) abnormalities have been observed in patients. These reports suggest that TLE is a network disorder. IGE is characterized by bilateral epileptic discharges prominently in the frontal lobe. Magnetic resonance images (MRI) of patients suffering from IGE appear normal.
    Diffusion tensor imaging (DTI) is sensitive to the WM microstructure in the brain. Tensor based tractography can reliably reconstruct large WM tracts in vivo. The integrity of WM tracts can be inferred through quantitative measurements performed on these reconstructed images. The research in this thesis attempts to track the acute stage of Wallerian degeneration after injury using DTI. The concomitant reduction of parallel and perpendicular diffusivities 1-2 days after injury may reflect beading and swelling of axolemma or other confounding physiological processes. DTI was used to probe WM abnormalities in subsyndromes of TLE. Patients with TLE and MTS were found to have more extensive WM abnormalities than TLE without MTS. The affected area extends beyond limbic WM to multiple extratemporal locations. Graph theoretical analysis provided further insight into the topological organization of the TLE brain network. Both global and local communication efficiency were impaired and the pivotal hubs were altered in TLE. It is unknown whether these white matter changes are progressive over time. A longitudinal study of TLE patients with and without surgery over a mean of six and a half years revealed Wallerian degeneration in the ipsilateral temporal WM but not in the contralateral side in the surgical patients. No progressive change was found in the non-surgical patients other than normal aging. Finally, two clinically similar subsyndromes of IGE, i.e. juvenile myoclonic epilepsy and IGE with generalized tonic-clonic seizures only, were demonstrated to have distinct patterns of GM and WM abnormalities, indicating that those subsyndromes of IGE are the result of different underlying disease mechanisms. Overall, quantitative DTI has revealed structural brain differences in epilepsy that are not visible on standard MRI.

  • Subjects / Keywords
  • Graduation date
    Fall 2013
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.