Abstracts

Rationale: Temporal lobe epilepsy (TLE) is one of the most common types of intractable epilepsies. Damage to the hippocampus and parahippocampal gyrus is commonly observed in both patients and animal models of TLE. However, the role of these structures, their interconnections and correlation with function remain unclear. This project proposes to unify structure and function in epilepsy by first refining both novel MRI structural imaging techniques and functional connectivity techniques for determining interdependencies between brain regions. Higher angular resolution diffusion imaging (HARDI) was used in patients with TLE to identify and evaluate gray and white matter changes in the limbic circuit to be correlated with functional changes seen using electroencephalography (EEG) to improve surgical targeting.Methods: Patients were recruited from the epilepsy monitoring unit of Shands Hospital at the University of Florida. 24/7 video-EEG data was recorded and 3T MR images were obtained. MRI was collected using a 3T Siemens Verio system. HARDI was collected in 64 directions with a b-value of 1000 s/mm2 and in 6 directions with a b-value of 100 s/mm2. For fiber tracking, the diffusion orientation distribution function (dODF) at each voxel was estimated using the method of Wisharts (MOW) approach. This post-processing method allows for the resolution of complex fiber structures such as crossing and kissing fibers within a voxel. Tractography was performed by seeding all voxels above a fractional anisotropy threshold of 0.01 with the following parameters: 64 seeds per voxel, a step size of 0.5 of the voxel length, with a turning angle threshold of 50 degrees at each step. Regions of interest were drawn in the hippocampus, amygdala, thalamus and the entorhinal cortex in order to filter out pathways of the limbic system.Results: Preliminary results showed that isotropic acquisition of HARDI data in patients allows fiber tracking of limbic system pathways. Additionally, a reduction in the number of fibers was observed on the side of the epileptic focus when compared to the contralateral side. Conclusions: Our future plans are to analyze fiber pathways and functional connectivity from EEG data, from a larger number of patients. We will then hybridize these techniques to allow for new advances in the understanding of a possible relationship between structure and function of the epileptic brain. Practically, this study will allow better definition and characterization of the seizure onset zone for more accurate and targeted surgical resection.