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BACKGROUND AND PURPOSE: Recently, there has been growing interest in the glymphatic system (the functional waste clearance pathway for the central nervous system and its role in flushing solutes (such as amyloid ß and tau), metabolic, and other cellular waste products in the brain. Herein, we investigate a recent potential biomarker for glymphatic activity (the diffusion tensor imaging along the perivascular space [DTI‐ALPS] parameter) using diffusion MRI imaging in an elderly cohort comprising 10 cognitively normal, 10 mild cognitive impairment (MCI), and 16 Alzheimer's disease (AD). METHODS: All 36 participants imaged on a Siemens 3.0T Tim Trio. Single‐SE diffusion weighted Echo‐planar imaging scans were acquired as well as T1 magnetization prepared rapid gradient echo, T2 axial, and susceptibility weighted imaging. Three millimeter regions of interest were drawn in the projection and association fibers adjacent to the medullary veins at the level of the lateral ventricle. The DTI‐ALPS parameter was calculated in these regions and correlated with cognitive status, Mini‐Mental State Examination (MMSE), and ADASCog11 measures. RESULTS: Significant correlations were found between DTI‐ALPS and MMSE and ADASCog11 in the right hemisphere adjusting for age, sex, and APoE ε4 status. Significant differences were also found in the right DTI‐ALPS indices between cognitively normal and AD groups (P <.026) and MCI groups (P <.025) in a univariate general linear model corrected for age, sex, and APoE ε4. Significant differences in apparent diffusion coefficient between cognitively normal and AD groups were found in the right projection fibers (P =.028). CONCLUSION: Further work is needed to determine the utility of DTI‐ALPS index in larger elderly cohorts and whether it measures glymphatic activity. [ABSTRACT FROM AUTHOR]