Microstructural analysis of Paramagnetic Rim Lesions in Multiple Sclerosis using diffusion-weighted Magnetic Resonance Imaging

Multiple Sclerosis (MS) is the most prevalent inflammatory disease of the central nervous system and Magnetic Resonance Imaging (MRI) is the go-to technique to assess this pathology in vivo. However, studying this type of pathology requires the acquisition of multiple MRI sequences, resulting in a large set of complex data in a non-standardized format. Moreover, the MRI techniques currently used in the clinic only partially correlate to MS disease severity and have thus limited prognostic relevance. In this context, identifying novel predictive MRI biomarkers, with a stronger correlation with clinical outcomes is needed. To address these issues, the BIDS Managing and Analysis Tool (BMAT) has been developed. It provides researchers with a user-friendly interface to create and manage datasets using the Brain Imaging Data Structure (BIDS), a format proposing a universal standard for naming and organizing neuroimaging data. In addition, this application allows the integration of different processing pipelines allowing to study advanced and pathologically more specific biomarkers of the disease. In the framework of this master thesis, a brain lesions segmentation pipeline giving information about the volumetry and location of brain lesions was integrated into BMAT. BMAT also allows for the analysis of paramagnetic rim lesions (PRL), a novel MRI biomarker which strongly correlate with patient's clinical disability. This thesis focused on characterizing PRL's microstructural changes using advanced diffusion-weighted MRI (DW-MRI). In 22 MS patients, we compared PRLs with control lesions using different microstructural models (DTI, NODDI, DIAMOND, MF) and found significant microstructural differences between these two types of lesions. In agreement with previous studies, this master thesis provides additional evidence that PRLs are associated with a more severe tissue damage in terms of axonal injury and inflammatory demyelination.