Geometric Distortions and Signal-To-Noise Ratio of Conventional and Inner Fields-of-View for T2*-Weighted Echo-Planar Imaging of the Spinal Cord

Geometric distortions and signal-to-noise ratios (SNR) of T2*-weighted echo-planar imaging (EPI) of the spinal cord are compared for conventional and inner-FOV acquisitions based on 2D-selective RF (2DRF) excitations. For conventional acquisitions, the required FOV increases with the in-plane object size yielding more pronounced distortions, prolonged echo times (TEs), and reduced SNR. For inner-FOV acquisitions, the FOV is small and independent of the object size yielding only minor distortions. The 2DRF pulse duration must be adapted for larger object sizes resulting in slightly prolonged TEs but overall TEs remain shorter and SNR values are larger than for conventional acquisitions.