9.4-Tesla magnetic resonance imaging in focal epilepsy patients with high-resolution surface-based profiling of focal cortical dysplasias.

Objective

The detection of subtle epileptogenic lesions such as focal cortical dysplasias (FCDs) is a clinical challenge in the management of drug-resistant focal epilepsy (DRFE). Ultra-high-field (UHF) magnetic resonance imaging (MRI) offers increased signal-to-noise ratios and spatial resolution compared to 3-T MRI and may improve diagnostic yield.

Methods

We recruited n = 21 DRFE patients (with 3-T MRI findings: two positive, three equivocal, 16 negative) undergoing presurgical workup and n = 20 healthy controls for 9.4-T MRI (.8 mm isotropic magnetization-prepared 2 rapid acquisition gradient echo [MP2RAGE], slabs of .375 × .375 × .8 mm T2*-weighted gradient echo) and 3-T MRI (magnetization prepared rapid acquisition gradient echo [MPRAGE], magnetization-prepared 2 rapid acquisition gradient echo [MP2RAGE], fluid-attenuated inversion recovery [FLAIR]) acquisitions. Visual review for possible epileptogenic lesions was performed by clinical experts. For histopathologically confirmed FCDs, we extracted surface-based quantitative features (cortical thickness, quantitative T1, FLAIR, T2*, and quantitative susceptibility mapping values) across cortical depths and distances from the lesion center and performed high-resolution cortical profiling of 9.4-T T2* values.

Results

In two patients with histopathologically confirmed FCD IIb, lesions were visible with distinct qualitative and quantitative features at both field strengths. One of these type IIb FCDs showed a focal cortical T2* reduction at 9.4 T that could be quantified via automated cortical profiling, consistent with the previously described "black line sign." No new epileptogenic lesions were identified at 9.4 T in 3-T MRI-negative patients, who also had no histological evidence of such lesions.

Significance

9.4-Tesla MRI findings in epileptogenic lesions underlying DRFE are consistent with those on 3-T MRI. UHF T2*-weighted sequences may be useful to detect the black line sign and thereby refine surgical or ablation targeting for some FCDs. Assessment of the diagnostic yield of 9.4-T MRI was limited by the lack of 3-T MRI-negative but histopathologically confirmed cases and by the unavailability of parallel transmit and FLAIR at 9.4 T. Further optimization of UHF protocols and analysis methods on larger cohorts may enhance clinically applicable diagnostic benefits.