Clinical applications of ultra-high field magnetic resonance imaging in multiple sclerosis

Abstract

Magnetic resonance imaging (MRI) is of paramount importance for the early diagnosis of multiple sclerosis (MS) and MRI findings are part of the MS diagnostic criteria. There is a growing interest in the use of ultra-high-field strength -7 Tesla- (7T) MRI to investigate, in vivo, the pathological substrate of the disease. Areas covered: An overview of 7T MRI applications in MS focusing on increased sensitivity for lesion detection, specificity of the central vein sign and better understanding of MS pathophysiology. Implications for disease diagnosis, monitoring and treatment planning are discussed. Expert commentary: 7T MRI provides increased signal-to-noise and contrast-to-noise-ratio that allow higher spatial resolution and better detection of anatomical and pathological features. The high spatial resolution reachable at 7T has been a game changer for neuroimaging applications not only in MS but also in epilepsy, brain tumors, dementia, and neuro-psychiatric disorders. Furthermore, the first 7T device has recently been cleared for clinical use by the food and drug administration.

Keywords: FDA clearance; Multiple sclerosis; central vein sign; gray matter lesions; iron imaging; sodium imaging; ultra-high field MRI; white matter lesions.

Figure 1.

White matter lesionn detection at 3T and 7T. 3T and 7T axial images obtained for a patient with multiple slcerosis. White matter demyelinating lesions are visualized in greater detail in the 7T T2-weighted (first column) and T1-weighted image (second column). Image resolution: 3T T2-weighted=0.5×0.5×3 mm³,T1-weighted= 0.8×0.8×0.8 mm³; 7T T2-weighted=0.7×0.7×0.7 mm³, T1-weighted=0.7×0.7×0.7 mm³.

Figure 2.

Perivenous distribution of multiple sclerosis lesions. 3 T FLAIR* (combined T2*-weighted MRI and FLAIR) images from four individuals with a variety of neurological conditions. In the patients with relapsing–remitting or primary progressive multiple sclerosis (MS), a central vessel is visible in most hyperintense lesions (arrows in magnified boxes). On the other hand, a central vein is absent from most of the lesions (arrowheads in magnified boxes) in the patient with migraine and the patient with ischaemic small vessel disease. Reproduced from Sati et al. [21] by permission of Nature Publishing Group (work is licensed under a Creative Commons Attribution 4.0 International License).

Figure 3.

7T axial images obtained for a patient with multiple slcerosis. Cortical lesion (arrow) is visualized on T1-weigthed sequence (A), T2-weighted sequence (B) and T2*-weighted sequence (C).

Figure 4.

A sagittal GRE image of the cervical spinal cord at 0.78 × 0.78 x 3 mm³ resolution (a) shows the positions of seven axial high-resolution (0.3 × 0.3 × 3 mm³) multi-echo image slices at vertebral levels C1 through C7 (b–h) where grey and white matter are clearly discernible. Images are courtesy of Dr. Junqian Xu, Ichan School of Medicine at Mount Sinai. Reproduced from Zhang et al. [66] by permission of John Wiley & Sons, Ltd.

Figure 5.

²³Na group maps. Mean to total sodium concentration (TSC), (intracellular sodium concentration) ISC and (intra- cellular sodium volume fraction) ISVF maps for patients with multiple sclerosis (respectively, A, C and E) and controls (respectively, B, D and F). In both groups, TSC appears higher while ISC and ISVF are lower in grey matter than in white matter. As intracellular molar content and cell volume are equal to zero in extracellular tissue, ISVF and ISC measurements in CSF are meaningless. Reproduced by Petracca et al. [67] by permission of Oxford University Press.