Imaging Markers of Neuroinflammation in Aging and Alzheimer's Disease and Related Dementia: A Narrative Review

Neuroinflammation represents a crucial pathophysiological process of cognitive decline during aging and may play an important role in the development of Alzheimer’s disease and related dementia (ADRD). Many magnetic resonance imaging (MRI) studies have investigated the extent and consequences of neuroinflammation in the elderly and in people at various stages of ADRD. These imaging tools allow quantification of blood-brain barrier (BBB) permeability, white and gray matter injuries, and functional loss of the brain. Here, we reviewed this literature and provided a summary of the pros and cons of these various imaging protocols. With a focus on neuroinflammation, studies that characterized structural and functional brain changes but did not relate the findings to neuroinflammation were outside the scope of this review. However, we provided a brief survey on studies combining multiple imaging modalities for readers to have a broader view on neuroinflammation, aging, and ADRD. We first introduced the techniques of MRI to study BBB dysfunction, neuroinflammation, gray and white matter deficits, and functional brain changes. In the second section, we focused on the studies of neuroinflammation during aging. Finally, we described the imaging studies of ADRD in the context of neuroinflammation. Collectively, studies indicate that aging and AD are marked by progressive BBB dysfunction linked to cognitive decline, whereas neural markers derived of diffusion tensor imaging, magnetic transfer imaging, MR spectroscopy, structural imaging, and functional connectivity provide insights into neuroinflammatory processes. This literature supports MRI’s potential as a non-invasive tool for monitoring neuroinflammation and disease onset and progression.