Diffusion-weighted imaging is a magnetic resonance imaging (MRI) technique that quantifies the random Brownian motion (diffusion) of water molecules within biological tissues. This methodological approach leverages specialized gradient pulses to encode the microscopic displacement of water, providing images whose contrast is weighted by the magnitude and anisotropy of diffusion. Its significance lies in its ability to non-invasively probe tissue microstructure and cellular environment, enabling the characterization of tissue integrity, cellularity, and architectural changes relevant to various physiological and pathological states, particularly in neuroscience and oncology.