Smoldering Inflammation in MS

This study is using advanced PET brain scans to measure "smoldering" (low-level, ongoing) inflammation in the brains of people with multiple sclerosis (MS), both before and after they start a high-efficacy disease-modifying treatment. The goal is to understand how well these treatments suppress hidden brain inflammation. **You may be eligible if...** - You are 18 or older with a confirmed MS diagnosis - You have active disease (at least one enhancing lesion on MRI in the last 6 months) - You have not previously been on long-term MS treatment (steroids for a relapse are okay) - You are about to start a high-efficacy MS treatment (such as ocrelizumab or natalizumab) - Your blood tests are within normal limits **You may NOT be eligible if...** - You have a specific low-binding genetic variant for a brain protein called TSPO (tested during screening) - You have allergies to the PET scan tracers used in the study - You cannot lie still for long periods or have contraindications to MRI (e.g., certain metal implants, severe claustrophobia) - You are pregnant or breastfeeding - You have insulin-dependent diabetes or kidney problems affecting gadolinium contrast Talk to your doctor to see if this trial is right for you.