Seizure-onset zone lateralization in temporal lobe epilepsy using 7T rs-fMRI: Direct comparison with 3T rs-fMRI

Resting-state functional magnetic resonance imaging (rs-fMRI) at ultra-high field strengths (≥7T) is known to provide superior signal-to-noise to comparable acquisitions at lower field strengths. In this study, we provide a direct comparison of the seizure onset-zone (SOZ) lateralizing ability of 7T rs-fMRI and 3T rs-fMRI.

We investigated a cohort of 70 patients with temporal lobe epilepsy (TLE). A paired cohort of 19 patients had 3T and 7T rs-fMRI acquisitions for direct comparison between the two field strengths. Forty-three patients had only 3T, and eight patients had only 7T rs-fMRI acquisitions. We quantified the functional connectivity between the hippocampus and other nodes within the default mode network (DMN) using seed-to-voxel connectivity, and measured how hippocampal-DMN connectivity could inform SOZ lateralization at 7T and 3T field strengths.

Differences in hippocampal-DMN connectivity ipsilateral and contralateral to the SOZ were significantly higher at 7T (Cohen's d = 0.51, p = 0.008) than at 3T (Cohen's d = 0.26, p = 0.68) when measured in the same subjects. We found that SOZ lateralization was superior at 7T (receiver-operating characteristic area under the curve [ROC AUC] = 0.97, 95% confidence interval [CI]: 0.92-1.00) than 3T (ROC AUC = 0.67, 95% CI: 0.36-0.98), for the same subjects scanned at both field strengths. Our findings were reproduced in extended cohorts of subjects scanned at either 3T or 7T. Our rs-fMRI findings at 7T, but not 3T, are consistent (Spearman ρ = 0.65, p = .01) with clinical fluorodeoxyglucose positron emission tomography (FDG-PET) lateralizing hypometabolism.

We show superior SOZ lateralization in patients with TLE when using 7T relative to 3T rs-fMRI, supporting the adoption of high field strength functional imaging in the epilepsy presurgical evaluation.