7T MRI in epilepsy

Background: Drug-resistant epilepsy (DRE) affects up to one-third of individuals with epilepsy, for whom surgery may offer the best chance of seizure freedom.Surgical evaluation relies heavily on MRI to detect structural lesions such as malformations of cortical development (MCD) and hippocampal pathology.Ultra-high field 7 Tesla (7T) MRI provides higher signal-to-noise ratio and thus higher spatial resolution and slightly different tissue contrast than conventional MRI and may improve lesion detection and presurgical assessment.Methods: This thesis comprises four studies with complementary designs.Paper I is a prospective imaging study examining microstructural differentiation within MCD using 7T tensor-valued diffusion MRI in 13 patients.Paper II is a prospective observational cohort study of 25 patients with MCD, assessing lesion morphology, heterotopia-cortex association, and comparison with prior 3T MRI.Paper III, a retrospective clinical cohort study, included 61 patients with drug-resistant temporal lobe epilepsy (TLE) and evaluated the added diagnostic and clinical value of 7T MRI within the presurgical workflow.Paper IV included 42 individuals with TLE and investigated associations between 7T-derived hippocampal subfield volumes and performance on verbal and non-verbal memory tests.Results: Diffusion MRI at 7T revealed microstructural heterogeneity within MCD lesions that was not visible on conventional MRI.Structural 7T imaging identified 112 MCD lesions and demonstrated frequent connections between heterotopia and cortex, while also uncovering subtle focal cortical dysplasia that was not appreciated at 3T.In the TLE cohort, 7T MRI added clinically meaningful information in >50% of patients by clarifying ambiguous findings, revealing new lesions, or excluding suspected abnormalities.In Paper IV, memory performance did not differ significantly between left-and right-sided TLE, and hippocampal subfield volumes showed only weak and inconsistent correlations with cognitive measures. Conclusion:7T MRI improved the detection, delineation, and microstructural characterization of epileptogenic lesions and provided added value in the presurgical evaluation of focal epilepsy.Although hippocampal subfield volumes at 7T were not strongly associated with memory function, the overall findings support integration of 7T MRI into advanced diagnostic pathways for DRE.