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The authors characterized the susceptibility mapping of cortical lesions in patients with MS (n=36) and compared it with neuropathologic observations (n=16). Neuropathologic analysis revealed the presence of an intense band of microglia activation close to the pial membrane in subpial cortical lesions or to the WM border of leukocortical cortical lesions. The quantitative susceptibility mapping analysis revealed 131 cortical lesions classified as hyperintense; 33, as isointense; and 84, as hypointense. They conclude that cortical lesion susceptibility maps are highly heterogeneous, even at individual levels and that the quantitative susceptibility mapping hyperintensity edge found in proximity to the pial surface might be due to the subpial gradient of microglial activation.

Abstract

Figure 2 from paper — Illustration of examples of cortical lesion appearance on the quantitative susceptibility map obtained with the total generalized variation algorithm from the 3D EPI susceptibility-weighted scan. Each panel denoted by a letter is divided in 3 subpanels: 1) QSM with contoured CL (*red line*); 2) QSM with a superimposed CL (red), the NAGM reference tissue used in the CL classification (yellow), and NAGM obtained from the segmentation of the 3D T1 MPRAGE (cyan); 3) QSM with superimposed the 3D double inversion recovery sequence, where the CL detection and segmentation was performed. *A–D*, Hypointense lesions. *E–H*, Hyperintense lesions. The classification of CLs was performed with a 2-sided t test between QSM estimates in the lesion (with subtracted the median value of the reference QSM value in the NAGM) and a zero mean Gaussian distribution. When the t test was significant and the mean of nQSM was greater (lesser) than zero, the lesion was classified as hyperintense (hypointense).

BACKGROUND AND PURPOSE

Quantitative susceptibility mapping has been used to characterize iron and myelin content in the deep gray matter of patients with multiple sclerosis. Our aim was to characterize the susceptibility mapping of cortical lesions in patients with MS and compare it with neuropathologic observations.

MATERIALS AND METHODS

The pattern of microglial activation was studied in postmortem brain tissues from 16 patients with secondary-progressive MS and 5 age-matched controls. Thirty-six patients with MS underwent 3T MR imaging, including 3D double inversion recovery and 3D-echo-planar SWI.

RESULTS

Neuropathologic analysis revealed the presence of an intense band of microglia activation close to the pial membrane in subpial cortical lesions or to the WM border of leukocortical cortical lesions. The quantitative susceptibility mapping analysis revealed 131 cortical lesions classified as hyperintense; 33, as isointense; and 84, as hypointense. Quantitative susceptibility mapping hyperintensity edge found in the proximity of the pial surface or at the white matter/gray matter interface in some of the quantitative susceptibility mapping–hyperintense cortical lesions accurately mirrors the microglia activation observed in the neuropathology analysis.

CONCLUSIONS

Cortical lesion susceptibility maps are highly heterogeneous, even at individual levels. Quantitative susceptibility mapping hyperintensity edge found in proximity to the pial surface might be due to the subpial gradient of microglial activation.

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Heterogeneity of Cortical Lesion Susceptibility Mapping in Multiple Sclerosis

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