[The visual pathways, from anatomical MRI to physiological with (f)MRI and tractography with diffusion tensor MRI (DTMRI)]

Abstract

Advances in MRI technology have led to a better knowledge of visual pathways (1984-2004), with a new descriptive anatomy and functional model. The authors first describe the technical development of MRI over the last thirty years, then describe and illustrate the new descriptive anatomy. Cephalic MRI reveals brain structures that were previously invisible, on different encephalic planes, in the optic pathways, horizontally from the cornea to the calcarin fissure (neuro-ocular plane (NOP), oblique trans-hemispheric neuro-ocular (OTNOP) and neuro-opto-tractal planes (NOTP)), in their orthogonal orientation upon the oculomotor pathways: head and axonal optic nerve pack (visual deutoneurons in their meninges), optic tracts, lateral geniculate bodies, optic radiations and the calcarian fissure. Comparative anatomy with the rhesus macaque is mentioned. Functional neuroanatomy (physiology) benefits from cine-MRI for ocular motricity (OD MRI), growth by the observation of myelinization in children, blood and CSF circulation by MR angiography, local blood volumes by perfusion imaging, neuronal quantification with inflammation or myelin regeneration by spectroscopy (MRS), brain mapping by functional MR ((f)MRI) measuring local CBF enhancement by paradigmatic stimulations. The recent functional imaging method, tractography (or diffusion tensor MRI (DTMRI)), using diffusion MRI techniques, natural vector calculations with diffusion tensor and software power for morphological and statistical directional results, represents the direction of projection, association and commissural white matter tracts. Normal examples are shown and some common clinical consequences are discussed.