Quantitation of myelin damage in optic nerve, brainstem, cervical spinal cord, and corpus-callosum in MS

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ABSTRACT A fundamental goal of neuroimaging is to discern, differentiate and quantitate: demyelination, remyelination, axonal injury and axonal loss in the central nervous system (CNS) disorders. For instance, multifocal lesions in Multiple Sclerosis (MS) that frequently effect CNS white-matter (WM), exhibit both demyelination and axonal loss. Demyelination and axonal loss result in disability impacting physical and mental health. Thus, quantification of demyelination, axonal injury and remyelination in the CNS will be a major step forward for early detection, monitoring of disease activity and importantly for clinical studies of potential neuroprotective and remyelinating therapies. Despite significant advances in MRI technology, these goals have not been fully achieved. Among the emerging advanced MRI methods for studying cervical spinal cord (CSC) WMs, DTI has been the most extensively studied. The conventional DTI metrics are affected to a greater degree by edema than by demyelination. This is because the signal change in routine low-b diffusion methods is dominated by water movement in extra-cellular space. From our extensive experience with DTI of CSC, we surmised that a modified approach with improved quantitation and reproducibility would be required. Therefore, we have developed a novel DTI method called ultrahigh-b Diffusion-Weighted MRI (UHb-DWI) that promises to distinguish demyelination, inflammation, and axonal injury in CNS. UHb-DWI takes advantage of known fiber direction, which makes data acquisition and signal processing significantly simple compared with the conventional DTI. As the UHb-DWI is matured to quantification of myelination in CSC white-matters, we plan to expand UHb- DWI to detect demyelination, remyelination, and axonal injury in other white-matter tracts in CNS, including anterior optic nerves, brainstem, cervical spinal cord, and corpus callosum. Therefore, the goals of this study are to: (a) correlate biomarkers measured with UHb-DWI with demyelination and axonal loss in an animal model of cord injury, (b) establish a reference library of healthy human CNS data in eight age/gender groups, and (c) acquire exploratory data on limited cohorts of patients with clinically isolated syndrome and optic neuritis to establish proof of concept for human applications. Upon successful completion of current work, we will have a powerful, non-invasive imaging method to characterize axonal density and demyelination in patients’ CNS. This may lead to earlier and more sensitive detection of clinically important spinal cord lesions or the ability to monitor the evolution of the cord during the treatment of patients with MS and other major CNS diseases including Neuromyelitis Optica, Optic Neuritis, Traumatic Brain Injury, Alzheimer’s Disease, and degenerative cervical myelopathy.