Assessment of Synaptic Density in MS

The investigators propose to use the novel SV2a-PET ligand, \[F-18\]SDM-8 to assess synaptic density in progressive multiple sclerosis (PMS) (including primary progressive multiple sclerosis (PPMS) and secondary progressive multiple sclerosis (SPMS)), given its improved imaging characteristics and potential for large scale applicability. The specific aims of the study are: Aim 1: To compare the cortical and subcortical grey matter synaptic density in PMS patients, patients with relapsing-remitting MS (RRMS), and healthy subjects, using a novel \[F-18\] labeled synaptic density PET ligand, \[F-18\]SDM8, also known as \[F-18\]SynvesT-1. Aim 2: To compare the relationship of synaptic density PET and standard 3T MRI measures including global and regional brain atrophy and lesion load with clinical measures of physical disability, cognitive impairment, fatigue and depression in MS patients. Aim 3: To assess the relationship of synaptic density PET with serum neurofilament light chain (NfL) and with serum measurements of inflammatory markers, IL-1β, TNF-α, IL-6, MCP-1 (Monocyte Chemoattractant Protein-1) and MIF-1 (Macrophage Migration Inhibitory Factor-1).