fractional anisotropy
Also written as: FA — fractional anisotropy
A DTI metric ranging from 0 to 1 that quantifies the degree of directional water diffusion within tissue microstructure.
Full Definition
Fractional anisotropy (FA) is a scalar measure derived from diffusion tensor imaging that quantifies the directional dependence of water diffusion within brain tissue. FA values range from 0 (completely isotropic diffusion) to 1 (completely anisotropic diffusion), with higher values typically indicating greater white matter integrity and fiber organization. FA is calculated from the eigenvalues of the diffusion tensor and serves as a sensitive marker of white matter pathology, developmental changes, and aging effects. Decreased FA often reflects tissue damage, while increased FA may indicate improved myelination or fiber coherence.
Usage
Usage note: Always specify the range when reporting values; often abbreviated as FA.
In Context
- "Fractional anisotropy was significantly reduced in the corpus callosum of patients with multiple sclerosis." — Research findings
- "FA values were extracted from the superior longitudinal fasciculus using probabilistic tractography." — DTI analysis methods