Abstract #3650

Examining Links Between Free Water and a TSPO-PET Marker of Neuroinflammation

Benjamin E. Reid¹, Maria Di Biase¹, Martin G. Pomper^2,3, Martha E. Shenton^1,4,5, Yong Du³, Jennifer M. Coughlin^2,3, and Ofer Pasternak^1,4

¹Psychiatry Neuroimaging Laboratory, Brigham and Women's Hospital, Boston, MA, United States, ²Department of Psychiatry and Behavioral Sciences, Johns Hopkins Medical Institutions, Baltimore, MD, United States, ³Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, Baltimore, MD, United States, ⁴Department of Radiology, Brigham and Women's Hospital, Boston, MA, United States, ⁵Research and Development, VA Boston Healthcare System, Boston, MA, United States

Free-water (FW) is a diffusion MRI marker of freely diffusing water in the extracellular space, which is expected to increase in the presence of neuroinflammation. Here, we test associations between FW and positron emission tomography (PET) imaging of the translocator protein (TSPO), which is a putative neuroinflammatory marker. We show that increased FW relates to higher TSPO binding in the hippocampi of healthy controls, but not of individuals with sports-related, repetitive traumatic brain injury. Thus, while FW relates to TSPO under healthy conditions, pathological variance in TSPO may complicate associations between FW and TSPO-indexed neuroinflammation.

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