This session examines diffusion MRI methods and applications centered on diffusion-weighted imaging and tensor-based techniques (DWI/DTI/DKI), with emphasis on microstructural characterization across neurological and systemic diseases. Presentations address diffusion tensor and kurtosis imaging, tractography-based analyses, and emerging diffusion visualization strategies, alongside longitudinal MRI frameworks supported by robust image registration. Clinical applications span multiple sclerosis, Alzheimer’s disease, traumatic brain injury, severe obstructive sleep apnea syndrome (OSAS), and IDH-mutant brain tumors. Special focus is given to diffusion-derived biomarkers such as the DTI-ALPS index and choroid plexus volume as indicators of microstructural change and fluid-related pathways. By integrating diffusion modeling, tensor imaging, and longitudinal analysis, the session highlights how diffusion MRI can reveal disease-specific trajectories and mechanisms relevant to clinical research and practice.