This is a 4-year, longitudinal study of 100 active-duty Navy SEALs. The goal of the study is to determine whether repeated blast exposure affects SEAL brain health and to develop an initial diagnostic testing protocol that detects repeated blast brain injury.

Participants will travel to Massachusetts General Hospital (MGH) in Boston, MA for a 1-day study visit at enrollment (baseline) and 1-year follow-up. At each visit to MGH, participants will have brain scans, blood tests, and assessments of cognitive performance, psychological health, and physical symptoms. Every 3 months between the baseline and follow-up visits to Boston, there will be brief (~1 hour) assessments via phone or video teleconference.

Inclusion Criteria:

1. Active-duty Navy SEAL Service Member
2. Early career SEAL (0-2 years) or mid-late career SEAL (10-15 years)
3. Age 18-50 years
4. Males, regardless of race or ethnicity

Exclusion Criteria:

1. History of moderate or severe TBI
2. History of major neurological disorder
3. Untreated or unstable severe psychiatric condition
4. Current severe medical condition that requires long-term treatment
5. Any condition that may cause undue risk to the participant or create a logistical contraindication
6. MRI contraindication
7. PET contraindication

USSOCOM regulations prevent public release of the data generated for the current study. Future requests for these data may be submitted to the corresponding author and will then need to be vetted by USSOCOM.

The investigators analyzing the MRI, cognitive, psychological, physical symptom, and exposure data will be blinded to the PRB28 TSPO PET results. Similarly, the investigators analyzing the PBR28 TSPO PET results will be blinded to all other data elements. The participants will be also be blinded to PBR28 TSPO PET results.