Fractional Anisotropy (FA) is a metric derived from diffusion tensor imaging (DTI), a magnetic resonance imaging (MRI) technique used to study the microstructural organization of tissues, particularly white matter in the brain. FA quantifies the degree of anisotropy of water diffusion within tissue. In white matter, water molecules tend to diffuse more easily along the direction of the fiber tracts (axonal bundles) than perpendicular to them. FA values range from 0 to 1, where higher values indicate greater directionality or organization of the tissue microstructure, typically reflecting intact white matter tracts.