Reduced field-of-view MRI using outer volume suppression for spinal cord diffusion imaging

A spin-echo single-shot echo-planar imaging (SS-EPI) technique with a reduced field of view (FOV) in the phase-encoding direction is presented that simultaneously reduces susceptibility effects and motion artifacts in diffusion-weighted (DW) imaging (DWI) of the spinal cord at a high field strength (3T). To minimize aliasing, an outer volume suppression (OVS) sequence was implemented. Effective fat suppression was achieved with the use of a slice-selection gradient-reversal technique. The OVS was optimized by numerical simulations with respect to T-1 relaxation times and B-1 variations. The optimized sequence was evaluated in vitro and in vivo. In simulations the optimized OVS showed suppression to < 0.25% and similar to 3% in an optimal and worst-case scenario, respectively. In vitro measurements showed a mean residual signal of < 0.95% +/- 0.42 for all suppressed areas. In vivo acquisition with 0.9 x 1.05 mm(2) in-plane resolution resulted in artifact-free images. The short imaging time of this technique makes it promising for clinical studies.