Comparison of brain volumetry in patients with non-lesional epilepsy on 3 and 7 T MPRAGE

7 Tesla (T) magnetic resonance imaging (MRI) provides more accurate image resolution than 3 T MRI due to its higher field strength. This could lead to a significant improvement in diagnostics, especially in small anatomical regions like the substructures of the hippocampus and amygdala. However, inhomogeneities arise due to higher field strengths, which could reduce this benefit. We compared current segmentations between 3 and 7 T in a clinical setup. The aim of this study was to evaluate the feasibility of FreeSurfer and FastSurfer at 7 T MRI in comparison to 3 T MRI. Since the hippocampus and amygdala also play an important role in epilepsy research, we additionally tested the FreeSurfer hippocampus scripts on both the FreeSurfer and FastSurfer segmentations.

As part of a prospective study, we performed both a 3 T MRI and a 7 T MRI on patients with non-lesional epilepsy initially diagnosed on 3 T. FreeSurfer and FastSurfer segmented and volumetrically measured both data sets using T1-weighted MPRAGE. We also performed hippocampal subfield volumetry and calculated inter-scanner variability.

We found significant differences between FreeSurfer and FastSurfer at both 3 and 7 T, with FastSurfer typically producing higher volumetric estimates. We detected significant deviations in FreeSurfer in the subsegmentation of the left hippocampus on 7 T caused by inhomogeneities. The hippocampus segmentation on 3 T demonstrated overall greater homogeneity.

Both methods and field strengths possess inherent advantages and limitations, resulting in differences in segmentation outcomes. Pre-processing can partially mitigate these discrepancies.