Cortical thickness variability in multiple sclerosis: the role of lesion segmentation and filling

Cortical Thickness (CTh) estimation from Magnetic Resonance Imaging (MRI) data of Multiple Sclerosis (MS) patients is biased at variable extent by the presence of white matter lesions. To overcome this limitation, several methods have been developed. In this study, we evaluate the impact on CTh measurements of different lesion corrections obtained combining three lesion segmentations (manual or automatic) with three intensity filling methods at whole brain and regional scale. Mean relative CTh differences (MRE) after lesion correction with automatic or manually-based methods was used to size the correction effects. Considered the full 3x3 factorial design, an analysis of variance was performed with lesion segmentation and filling as factors. The estimated CTh was remarkably similar between manually-based (gold standard) and automatic corrections with MRE generally well under 2% in all pairwise comparisons and spatial scale. However, a higher MRE was observed using FSL filling. Although the overall CTh agreement, these results suggest that the lesion filling approach provided with FSL library (FMRIB group, Oxford, UK), regardless of the lesion segmentation method used, can deliver an underestimation in the order of 1% of MRE compared to other corrections.