RecruitingDrug trialThis Study Involves a Positron Emission Tomography (PET) Scan Using a New Investigational Radioactive Tracer, [18F]-FZTA, to Detect Inflammation in the Brain. The Tracer Will be Tested in Healthy Younger Adults and Individuals With Multiple Sclerosis.This study involves a Positron Emission Tomography (PET) scan using a new investigational radioactive tracer, \[18F\]-FZTA, to detect inflammation in the brain. The tracer will be tested in healthy younger adults and individuals with Multiple Sclerosis.