In vivo detection of cortical plaques by MR imaging in patients with multiple sclerosis

Abstract

Background and purpose: In vivo detection of cortical lesions in patients with multiple sclerosis (MS) by MR imaging is hampered by several factors. Among them is the low contrast between small cortical lesions and surrounding cortical gray matter offered by present techniques.

Methods: T1-weighted 3D spoiled gradient-recalled-echo (SPGR) volumes and 2D fluid-attenuated inversion recovery (FLAIR) sequences of 22 patients with MS who had 12 monthly brain MR imaging examinations at 1.5T, using a quadrature head coil, were retrospectively analyzed. These serial studies were coregistered and averaged to generate a single high signal-to-noise ratio (SNR) mean image, which was used to identify cortical lesions. The means of 12 FLAIRs and SPGRs from 14 age- and sex-matched healthy volunteers were analyzed as well.

Results: No cortical lesions were found on images of healthy subjects. Eighty-six cortical lesions were identified in 13 (59.1%) patients, predominantly in the frontal lobe (73.3%); 23.3% of cortical lesions lay entirely in the cortex, whereas the remaining lesions invaded the white matter underneath.

Conclusion: Averaging multiple SPGRs created a single high SNR volume, allowing identification of cortical lesions. Because data were obtained monthly for 1 year, the average image does not account for transient lesion activity. However, for cortical lesions that remained stable during this time, the findings are valid in demonstrating the importance of high SNR images for detecting cortical brain abnormalities in MS.

Fig 1.

Average of 12 coregistered axial SPGR (A) and FLAIR (B) MR images demonstrate cortical MS lesions in patient 3. Several Type B cortical lesions traverse the gray-white boundary (white arrowheads, A, B). A single Type A lesion (white arrows A, B) is confined to the gray matter of the motor strip. Serial magnified images of the precentral gyrus (C-J) conform that this lesion (white arrows D-H) does not extend into the juxtacortical white matter.

Fig 2.

Average of 12 coregistered SPGR (A) and FLAIR (B) demonstrate a Type B cortical lesion in the right insula (arrowheads). Higher magnification of the averaged SPGR dataset in the axial (C), coronal (D), and sagittal (E) planes shows the relationship of the lesion to the cortical ribbon. (Patient 2).

Fig 3.

Coregistration and averaging 6 (B) and 12 (C) T1 SPGR MRI volumes improves conspicuity of cortical lesions (e.g. Type B lesion arrows, A-C) relative to a single SPGR (A). Although the Type B lesion is visible on the single SPGR (A), coregistering and averaging 6 (B) and 12 (C) SPGRs improves lesion conspicuity, and allows clear characterization of lesion location with respect to the gray-white boundary. (Patient 6).