This session focuses on advanced diffusion MRI methods for probing brain microstructure, barrier integrity, and fluid–tissue interactions in neurodegenerative and systemic diseases associated with cognitive impairment. Presentations will cover diffusion tensor–based and higher-order tensor imaging (DWI/DTI/DKI), time-dependent and microstructure-informed diffusion modeling, and emerging diffusion visualization techniques that improve anatomical and physiological interpretability. Disease-oriented applications include Alzheimer’s disease and mild cognitive impairment, Parkinson’s disease, Wilson disease, and cognitive dysfunction related to chronic kidney disease. Special emphasis is placed on subcortical U-fibers, white matter microstructure, free-water and cerebrospinal fluid contributions, and diffusion-based markers of blood–brain barrier and glymphatic system dysfunction. By integrating diffusion acquisition strategies, modeling innovations, and clinically relevant phenotypes, the session highlights diffusion MRI as a powerful tool for mechanistic insight and translational research in disorders of cognition.