Low-level Blast Exposure

The goal of this observational study is to learn about the impact of low-level blast exposure in U.S. Special Operations Forces personnel. The main questions it aims to answer are: What advanced brain imaging changes are related to clinical presentation after low-level blast exposure? What are the relationships between low-level blast exposure and common groups of symptoms after concussion? Participants will: * Undergo advanced brain imaging * Answer questionnaires * Complete clinical tests * Provide blood, urine, and saliva samples * Wear blast sensors