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.

Inclusion Criteria:

* Male or female, any race
* Age ≥ 18 years
* Capable of providing written informed consent for volunteering to undergo research procedures.
* Healthy volunteer or volunteer with a diagnosis of MS established using the revised McDonald criteria (2017)

Exclusion Criteria:

* Hypersensitivity to \[18F\]FZTA or any of its excipients;
* Contraindications to PET, CT, or MRI (e.g., certain incompatible electronic medical devices, inability to lie still for extended periods) that make it potentially unsafe for the individual to participate.
* Severe claustrophobia
* Women who are currently pregnant or breastfeeding
* Currently undergoing radiation therapy
* Any condition that, in the opinion of the Sponsor-Investigator or designee could increase risk to the participant, limit the participant's ability to tolerate the research procedures, or interfere with the collection of the data (e.g., renal or liver failure, advanced cancer);
* Participants who in the last 6 months experienced any of the following cardiovascular conditions or findings in the screening electrocardiogram (ECG): clinically significant cardiac arrhythmias including atrial fibrillation with rapid ventricular response, myocardial infarction, high-grade heart block (type 2 or greater), unstable angina, stroke, transient ischemic attack or decompensated heart failure requiring hospitalization or Class III/IV heart failure;
* Current or recent (within 12 months prior to screening) participation in research studies involving radioactive agents such that the total research-related radiation dose to the participant in any given year would exceed the limits set forth in the U.S. Code of Federal Regulations (CFR) Title 21 Section 361.1.