Diehl, B.; (2011) Imaging correlates of the epileptogenic zone and functional deficit zone using diffusion tensor imaging (DTI). Doctoral thesis , UCL (University College London).

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Abstract

Focal epilepsy is a common serious neurologic disorder. One out of three patients is medication refractory and epilepsy surgery may be the best treatment option. Neuroimaging and electroencephalography (EEG) techniques are critical tools to localise the ictal onset zone and for performing functional mapping to identify the eloquent cortex in order to minimise functional deficits following resection. Diffusion tensor magnetic resonance imaging (DTI) informs about amplitude (diffusivity) and directionality (anisotropy) of diffusional motion of water molecules in tissue.This allows inferring information of microstructure within the brain and reconstructing major white matter tracts (diffusion tensor tractography, DTT), providing in vivo insights into connectivity. The contribution of DTI to the evaluation of candidates for epilepsy surgery was examined: 1. Structure function relationships were explored particularly correlates of memory and language dysfunction often associated with intractable temporal lobe epilepsy (TLE; chapters 3 and 4). Abnormal diffusion measures were found in both the left and right uncinate fasciculus (UF), correlating in the expected directions in the left UF with auditory memory and in the right UF with delayed visual memory performance. Examining the arcuate fasciculus (AF), bilateral diffusion changes were found with correlations between left AF DTI measures and language scores. 2. The second aim of this thesis was to validate DTT results and test the hypothesis that cortical language areas determined by cortical stimulation serve as anchor points for the tractography defined AF (chapter 5). Subdural grid contacts overlying anterior language cortex co-localised in 84.2% with the AF, and in 55.8% in posterior language areas. This provides some validation that the AF reconstructed using DTT subserves language function, but further study is needed. 3. Lastly, seizure propagation was investigated in a case series of patients with cortical dysplasia (chapter 6). Reduced connectivity with reduced arborization and thinning of the fibre bundles between subcortical WM and the dysplastic cortex was demonstrated. Fibre tracts reconstructed from regions underlying the ictal onset zone showed abnormal connectivity.

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