Contiguous-slice zonally oblique multislice (CO-ZOOM) diffusion tensor imaging: examples of in vivo spinal cord and optic nerve applications.

PURPOSE: To describe and demonstrate a new technique that allows diffusion tensor imaging of small structures such as the spinal cord (SC) and optic nerve (ON) with contiguous slices and reduced image distortions using a narrow field of view (FOV).
MATERIALS AND METHODS: Images were acquired with a modified single-shot echo-planar imaging (EPI) sequence that contains a refocusing radio frequency (RF) pulse in the presence of the phase-encoding (rather than slice-select) gradient. As a result, only a narrow volume may be both excited and refocused, removing the problem of signal aliasing for narrow FOVs. Two variants of this technique were developed: cardiac gating is included in the study of the SC to reduce pulsation artifacts, whereas inversion-recovery (IR) cerebrospinal fluid (CSF) suppression is utilized in the study of the ON to eliminate partial volume effects. The technique was evaluated with phantoms, and mean diffusivity (MD) and fractional anisotropy (FA) measurements were made in the SC and ON of two healthy volunteers.
RESULTS: The technique provides contiguous-slice, reduced-FOV images that do not suffer from aliasing and have reduced magnetic susceptibility artifacts. MD and FA values determined here lie within the ranges quoted in the literature.
CONCLUSION: Contiguous-slice zonally orthogonal multislice (CO-ZOOM-EPI is a new technique for diffusion-weighted imaging of small structures such as the ON and SC with high resolution and reduced distortions due to susceptibility variations. This technique is able to acquire contiguous slices that may allow further nerve-tracking analyses.