[Tractography of the visual pathways: routine examination in magnetic resonance imaging]

Water diffusion analysis in magnetic resonance imaging (MRI) provides an elective visualization of fiber tract orientations in cerebral white matter, especially for optic tracts. We explored 25 patients from 18 to 45 years of age, with normal MRI in 20 subjects, and radiological anomalies in five. On a 1.5 Tesla MRI apparatus, diffusion tensor acquisitions were performed in 5 minutes 58 seconds with an EPI Single Shot sequence covering the entire brain. Image displacements were precluded by patient information and adequate fixation, then digitally corrected on workstations. Volume merging and fiber tract extraction were achieved using dedicated software (Volume-One and dTV). A directional depiction was obtained for all areas in the white matter, in particular for white matter junctions. Coming from the lateral geniculate body, the optic tracts were directed posteriorly toward the occipital cortex, with numerous connections to extrastriate associative areas, and through the corpus callosum and the fornix. Diffusion tractography requires optimization of volume displacements, before and secondary to MRI acquisitions. Our diffusion tensor acquisition, with image optimization in a short-duration sequence can be routinely applied to all patients, for a specific analysis of functional connections between cortical areas of cerebral white matter.