Arterial Spin-Labeling MRI at the Cortical-CSF Interface: A Novel Biomarker in Alzheimer Disease.

BACKGROUND/OBJECTIVE: Arterial spin-labeling (ASL) MRI can measure perfusion signal adjacent to CSF spaces and may provide information regarding CSF-adjacent water transport physiology. We developed an automated pipeline to extract cortical-CSF interface (IF) perfusion for comparison between Alzheimer disease (AD) and cognitively normal controls. METHODS: In this retrospective study, participants with AD and cognitively normal controls with ASL and 3D T1-weighted MRI were included. Parenchymal cerebral blood flow (CBF) was evaluated globally (whole brain, gray matter, white matter) and across 12 brain regions. IF-perfusion values were quantified using an automated pipeline with tissue segmentation, registration, partial-volume-aware masking, and arterial-signal exclusion. Multivariable sensitivity analysis was performed, adjusting for age, sex, scanner vendor, and acquisition site. Predictive modeling was performed using LASSO-regularized logistic regression with nested repeated stratified cross-validation, and feature contributions were summarized using SHAP. RESULTS: A total of 51 patients with AD, age (median: 73 years) and 53 cognitively normal subjects (median age: 69) were included. Global CBF did not differ between groups. However, IF-perfusion values were significantly lower in AD (median 4.4, IQR 3.2-4.8) than in controls (median 5.2, IQR 4.5-6.3; p < 0.001). In multivariable analysis, AD remained independently associated with lower IF-perfusion after adjustment for age, sex, scanner vendor, and acquisition site (β = -1.88, 95% CI: -3.52 to -0.25; p = 0.025). In LASSO-regularized logistic regression model, only IF-perfusion and cuneus-CBF remained as significant contributing features for the prediction of AD probability with the highest contribution from IF. The final model showed mean ROC-AUC 0.81 in the training and AUC of 0.78 in the testing dataset. CONCLUSION: ASL-derived IF-perfusion is reduced in AD and may represent a promising imaging marker of altered CSF-adjacent water transport physiology. Further validation against established biomarkers of CSF dynamics and clearance pathways is warranted.