Date of Award
2007
Degree Type
Thesis
Degree Name
Doctor of Philosophy
Program
Medical Biophysics
Supervisor
Dr. Robert Bartha
Second Advisor
Dr. Warren Blume
Third Advisor
Dr. Dick Drost
Abstract
Focal epilepsy disorders involve seizures that originate from a specific region of brain tissue, and are often resistant to medication. Surgical intervention can be an effective treatment for intractable focal epilepsy patients whose seizure focus has been confidently localized. In addition to the clinical localization protocol of electroencephalography (EEG) and structural magnetic resonance imaging (MRI), proton magnetic resonance spectroscopy (1H MRS) and simultaneous EEG and functional MRI (fMRI) have great potential for sensitively localizing epileptogenic tissue. The research presented in this thesis involves the application of 1H MRS to temporal lobe epilepsy (TLE) patients, and the development of MR compatible EEG hardware that can allow for high magnetic field EEG∕fMRI studies. 1H MRS was used to detect brain metabolite imbalances that were specific to the epileptogenic tissue in strongly Iateralized MRI-negative TLE patients. Decreases in the neuronal marker N-acetylaspartate (NAA) and increases in the combination of the excitatory neurotransmitter glutamate and its intermediate compound glutamine were observed in the epileptic temporal lobe when compared with the contralateral side. A quantitative method for assessing the MR compatibility of EEG scalp electrodes based on B0 distortions, B1 shielding, and heating effects was applied to three different types of electrodes. The interactions between conductive wires and the radiofrequency (RF) fields were also investigated. The magnitude of the interaction was evidenced by induced B1 excitation image artifacts and heating effects, and showed a distinct variation with wirelength. 10 cm was determined as the maximum safe wirelength when performing superficial monitoring applications with 4 Tesla MRI. Finally, resonant lengths of wire were segmented with non-ferromagnetic RF chokes to avoid the generation of strong B1 artifacts and heating effects. RF choke bisection reduced the amount of artifact and heating by up to 90%. Preliminary testing on a prototype high field MR compatible EEG system based on these findings is presented. iii The results obtained suggest that high field 1H MRS may aid in the identification of MRI-negative epileptogenic tissue. MRI compatible EEG systems can be produced for use at high fields that generate minimal image distortion and heating, allowing their safe use in simultaneous EEG/fMRI applications.
Recommended Citation
Stevens, Todd K., "Magnetic Resonance Investigations of Focal Epilepsy" (2007). Digitized Theses. 4957.
https://ir.lib.uwo.ca/digitizedtheses/4957