Spinal Cord Magnetic Resonance Imaging at Ultra High Field: version 2.0 – 7T-SC-MRI-2-0

Spinal cord (SC) Magnetic Resonance Imaging (MRI) has greatly improved over the last decade, however it still remains underexplored : assessing subtle details such as small lesions or the central vein sign, which may change the diagnosis of Multiple Sclerosis (MS) for instance, is not yet possible; confident characterization of tissue impairment in small regions of interest such as anterior gray matter (containing the motoneurons) or lesion rim (characterizing chronic activity), is not yet possible either; and prognosis factors that would help for individual patient management (therapeutical or surgery decision) are also missing.
In this context, Ultra-High Field (UHF) MR systems have opened promising avenues, allowing to acquire high-resolution and high-contrast images.

Great achievements have been performed over the last few years for 7T SC MRI, including active contributions from our group. However, we have reached a state where new solutions must be investigated, to go beyond these exploratory works, and to offer the full potential of 7T MRI for spinal cord disease characterization.
Indeed, while implementing 7T SC MRI for clinical research studies, various issues have been encountered. Specifically, challenges inherent to UHF MRI, such as the inhomogeneity of the transmit magnetic field and high energy deposition in tissue, currently limit the performance of MR sequences in the cord in single channel imaging. As a consequence, spatial coverage may be reduced, and bias may be present in quantitative measurements. Furthermore, the lack of RF hardware currently limits investigations to the cervical cord, whereas thoracolumbar exploration would be required as well, in particular for pathologies such as MS. Finally, methods for a better detection and characterization of lesions in the cord are required, together with a better description of gray matter involvement.

Based on recent works, strong experience, and a consolidated consortium gathering complementary and interdisciplinary expertises from CRMBM-CEMEREM, Institut Fresnel and APHM, the 7T-SC-MRI-2.0 project aims at proposing an embedded framework of cutting-edge tools that will deliver increased sensitivity and deeper insights into the spinal cord diseases. Pushed by clinical needs, we intend to particularly focus on:
1) imaging of the whole cord (and not only the cervical level), by proposing new radiofrequency (RF) coils in rupture with traditional designs and including flexible metasurface pad;
2) reduction of RF energy deposition and improvement of anatomical and quantitative 7T MR sequences performance, by developing tailored imaging strategies based on parallel transmission (pTx);
3) detection of lesions, vascular abnormalities and lesion activity (for refined diagnosis and better understanding of pathology mechanisms), by providing adequate and dedicated contrasts;
4) facilitation of knowledge extraction and visualization of pathologically relevant features that could not be observed on conventional scanners (eg. central canal, gray matter substructures, or small tracts), by building dedicated spinal cord multi-atlases allowing automatic analyses and refined characterization of specific deficits.

Planned for 4 years, the 7T-SC-MRI-2.0 will first focus on Multiple Sclerosis, for which early cord lesion detection, classification scheme, and identification of individuals at risk of worse outcomes is critical. But the techniques will more generally benefit to all neurodegenerative and traumatic spinal cord diseases.