Fractional Anisotropy Maps

Main Cerebral Tracts on Orthogonal Fractional Anisotropy maps

Cerebral tracts may be presented in 2D color images in: axial, coronal, and sagittal planes.   The relational topographic appearance of the tracts are better identified in planes that are perpendicular to the major axis of the tract.  For example, the corpus callosum which is an axial structure is better defined in the sagittal or coronal view.  Thus, tracts going anterior-posterior or posterior-anterior are better seen in coronal view.  Descending and ascending tracts are better depicted in axial view (Figure 1).

Figure 1.  Axial FA Map.  We have targeted blue fibers which encodes for foot-head or head-foot direction.  Ext.: External..  IC: Internal Capsule.  IOFF:  Inferior Occipito-Frontal Fasciculus.  Post.: Posterior.  Cort: Cortical.  Thal: Thalamic.  Bulb: Bulbar.  ILF:  Inferior Longitudinal Fasciculus.  Notice that the portion of the ILF and IOFF shown are just some bundles ascending in the posterior portions as these fasciculi are predominantly posterio-anterior oriented.

Coronal view (figure 2) is better to show the fibers oriented posteior-anterior or anterior-posterior, coded in green.

Figure 2. Coronal FA Map.  SOFF:  Superior Occipito-frontal Fasciculus.  SLF: Superior Longitudinal Fasciculus.  IOFF: Inferior Occipito-frontal fasciculus. ILF: Inferior Longitudinal Fasciculus.  SCP:  Superior Cerebellar Peduncle.

The sagittal plane (figure 3) best provides information on interhemispherical fibers going right to left or viceversa (red) or anterior-posterior (green).  These are the corpus callosum and the anterior commissure.

Figure 3. Saggital FA Map. Interhemispheric fibers are red in the midsagittal cut. Horizontal portion of the cingulum above the corpus callosum appears green. The green bundle in the inferior left corresponds to the medial part of the superior cerebellar peduncle. Subcortical U fibers appera various colors due to multiple intersecting planes.