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.

The primary objective of this initial IND study is to evaluate the safety of [18F]-FZTA for PET imaging of S1P1 expression. The study will begin with whole-body PET dosimetry in healthy adult volunteers to determine the safety and safe radiation dose for a single PET scan in humans. Following this, brain and neck imaging will be conducted in both healthy adult control participants and individuals with multiple sclerosis (both male and female) to characterize [18F]-FZTA uptake in the brain. An analysis of the radiolabeled metabolite will also be completed as part of this study.

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.

Aim 1: Dosimetry/Safety group will consist of 10 healthy adult normal volunteers (5 males and 5 females) who will be recruited and undergo whole-body PET/CT imaging to assess the safety, dosimetry, and metabolism of [F-18]FZTA. All 10 participants will also undergo a short MRI without contrast.

Aim 2: Proof of Concept/Healthy Cohort will consist of 15 healthy adult volunteers (Males and Females).

Aim 3: Proof of Concept/MS cohort consists of 10 MS patients who are on stable therapy.

Aim 4: Proof of Concept/MS cohort consists of newly diagnosed 20 RRMS patients who will be started on high-efficacy drugs.

Aims 2,3, and 4 will undergo [F-18]FZTA PET imaging of the brain and neck, brain MRI, and an optional [C-11]CS1P1 and [F-18]FDG PET imaging.