High spatial resolution combined with high contrast enabled the detection of white and gray matter pathology. The amount of artifacts was relatively minimal: one subject exhibited slight motion artifacts (blurring), and one subject exhibited Eddy-current artifacts. Susceptibility artifacts were noticeable in all subjects (patients and controls) in the sinus area, yielding slight signal decrease in the posterior part of the lower brain. Manual registration (gross alignment) was performed on about 90% of the subjects to ensure maximal robustness of fine registration on surfaces. However, since the pre-registration was relatively accurate (i.e., 7T MPRAGE on the 3T MEMPRAGE using FSL FLIRT), less than one minute per slab was required to slightly adjust each slab to the surface. Visual inspection confirmed that all 7T images were successfully registered to the surface. shows an axial view of a FLASH image from an SPMS patient. A zoomed panel focuses on a cortical lesion (arrow) and shows the result of segmentation with delineation of the pial surface (red) and GM/WM boundary (yellow). Surface mapping yielded relatively homogeneous signal for healthy subjects and visible hyperintensities in MS patients. shows an example of T2*-weighted signal mapped at 50% depth for a control (left) and another SPMS patient (right) where lesions appear as hyperintensities (arrows).
Figure 3 A. 7T FLASH image of a patient with SPMS. Zoomed panel shows an overlay of pial (red) and white matter surfaces (yellow). The right zoomed panel shows the reconstructed white matter surface of the same patient with T2*-weighted signal mapped on the surface. (more ...)
The GLM analysis detected significant differences between control and MS patients (). Overall, patients showed increased subpial T2* signal compared to controls in several areas of the frontal, temporal and parietal lobes of both hemispheres (). Changes were also detected in occipital areas, mostly on the left hemisphere.
Figure 4 Overlay of the GLM significance maps (-log10(p)) on the average pial surface for all patients (N=17) versus controls (N=9). Most significant changes in T2*-weighted signal occur in the lateral occipital (1), left parsopercularis (2), sensorimotor region (more ...)
Brain cortical areas showing significantly increased subpial T2* signal in 17 patients with multiple sclerosis compared to nine age-matched controls.
We tested the effect of gender on our MR measures by adding a regressor on the GLM analysis. Results showed no significant effect of the gender regressor throughout the cortex (P<0.05, uncorrected).
We also tested the effect of using the 8-channel coil versus the 32-channel coil, by excluding subjects scanned with the 8-channel coil. Despite slight differences between the two analyses – that could be accounted by different population size, results produced with or without the 8-channel coil were very similar.
The total area of hyperintensities in cortical gyri was two times greater than that in sulci when comparing MS patients versus controls: the number of vertices (normalized by the total number of vertices) exhibiting significant signal changes was 0.0367 in sulci and 0.0679 in gyri.
shows Spearman’s correlations (thresholded at P=0.05) between subpial T2* signal and white matter lesion load. Significant positive correlations were detected in the lateral orbitofrontal, superior parietal, cuneus, precentral and superior frontal regions. Very few negative correlations were detected and were localized in the right middle temporal and the left lingual areas.
Figure 5 Spearman’s correlation coefficien between T2* signal and white matter lesion load. Results are slightly smoothed (FWHM=3mm) and thresholded (P<0.05). Significant correlations are detected in the lateral orbitofrontal (1), cuneus (2), precentral (more ...)
shows correlation between EDSS score and T2*-weighted signal averaged in the precentral gyrus was also significant (R=0.56, P=0.02), suggesting a relationship between T2* hyperintensities caused by GM pathology in the primary motor cortex and motor deficits.
Spearman’s correlation between EDSS score and T2*-weighted signal averaged in the precentral gyrus (R=0.56, P=0.02). For this analysis one subject was removed because part of his precentral gyrus was out of the field of view.