Quantitative susceptibility mapping at 7T as a biomarker of post- and interictal extravascular iron in patients with focal epilepsy.

BACKGROUND

Iron deposition in the brain has been associated with epilepsy, but its anatomical distribution and its temporal association to seizures remain unclear. Here, we investigate brain iron in individuals with focal epilepsy using interictal and postictal quantitative susceptibility mapping (QSM) at 7 T MRI and explore its functional relevance.

METHODS

80 consecutive participants with focal epilepsy undergoing presurgical evaluation and 50 healthy controls were included. 8/80 participants with focal epilepsy had interictal and postictal scans. High-resolution T1- and susceptibility-weighted images were acquired and processed using custom pipelines for QSM. Seizure onset zones were determined by expert consensus, and neuropsychological assessments included memory and mood. Parcel-wise analyses examined group differences and correlations with cognitive scores, controlling for age and sex.

FINDINGS: Participants with focal epilepsy showed significantly higher interictal susceptibility, which colocalised with the presumed seizure onset zone. Impaired memory performance and more severe depressive symptoms were correlated with higher interictal susceptibility. Postictal susceptibility was significantly higher than interictal susceptibility and associated to the number of preceding seizures.

INTERPRETATION: QSM reflects both ictal iron extravasation and interictal iron accumulation. If further validated, it may help to non-invasively delineate the epileptogenic zone and become a long-term biomarker for seizure-burden.

FUNDING: N.R.H. and T.Bauer were supported by the BONFOR research commission of the Medical Faculty of the University of Bonn. T.Bauer was funded by the Deutsche Forschungsgemeinschaft. T.Bauer., L.W., A.L. and T.R. are funded by the German Ministry for Research, Technology and Space.