Measuring Active Microglia in Progressive Multiple Sclerosis

This is pilot study designed to quantifying the innate immune inflammatory burden in a cohort of secondary progressive multiple sclerosis subjects. Innate immunity is recognized as a major cause of tissue injury in central nervous system (CNS) disease. Our hypothesis is that the innate immune response is heightened in SPMS as compared to healthy controls (HC's) and this activity increases over time and correlates with ongoing neuronal loss and disability. The investigators will test this hypothesis by using highly specific molecular imaging techniques, specifically PET, in conjunction with high field MRI. The investigators will utilize the PET radioligand \[11C\]PK11195 which will be used as a marker of activated macrophages/microglia. The investigators will correlate \[11C\]PK11195 uptake with conventional measures of inflammation and neuronal integrity on high-resolution MRI. SPMS subjects will have two baseline \[11C\]PK-11195 PET scans (separated by 24 to 72 hours, test-retest) and subsequent scans at 6, 12 and 24 months. SPMS Subjects will have brain MRI's at baseline, 6, 12 and 24 months. Healthy Controls will have 2 baseline PET scans and one MRI.