In vivo diffusion tensor imaging of the human optic nerve: Pilot study in normal controls

Diffusion tensor imaging (DTI) of the optic nerve (ON) was acquired in normal controls using zonally oblique multislice (ZOOM) DTI, which excites a small field of view (FOV) using a fast sequence with a shortened EPI echo train. This combines the benefit of low sensitivity to motion (due to the single-shot acquisition used), with the additional advantage of reduced sensitivity to magnetic field susceptibility artifacts. Reducing the bright signal from the fat and cerebrospinal fluid (CSF) surrounding the nerve are key requirements for the success of the presented method. Measurements of mean diffusivity (MD) and fractional anisotropy (FA) indices were made in a coronal section of the middle portion of the optic nerve (ON) in the right (rON) and left (ION) ONs. The average values across 10 healthy volunteers were FA(rON) = 0.64 +/- 0.09 and FA(ION) = 0.57 +/- 0.10, and MD(rON) = (1173 +/- 227) x 10(-6) mm(2) s(-1) and MD(ION) = (1266 +/- 170) x 10(-6) mm(2) s(-1). Measurements of the principal eigenvalue of the DT and its orthogonal component were also in agreement with those expected from a highly directional structural organization.