Apparent fiber density (AFD) examines fiber orientation in a voxel or a pixel. This technique is valuable in epilepsy because it allows neurologists to perform quantitative assessment of specific fiber tracts, examine the integrity of fiber bundles in a specific tract quantitatively, and determine whether a given fiber bundle has fewer axons. In a patient with hippocampal sclerosis, for example, an AFD-based study can show abnormalities in the parahippocampal region, fornix, and mesial temporal tracts on the ipsilateral side. Other techniques may not indicate these abnormalities.
Some of the powerful imaging techniques that are emerging are useful for individual diagnosis, and others are helpful for group studies. “This field is going to explode over the next five to 10 years,” because the current state of imaging technology recalls the situation at the start of “the genetics revolution,” concluded Dr. Jackson.
—Erik Greb