REST-PEEP: reduced scan time phase-encoded echo planar imaging

Echo planar methodology can be used for rapid acquisition in three dimensions of k-space. There are two groups of sequences which have thus far been implemented. The first group is characterized by three-dimensional acquisition from a single RF excitation. Echo planar shift mapping and echo volume imaging are single-shot chemical shift imaging and three-dimensional spatial imaging techniques, respectively. Even though these methods are extremely fast, their spatial and spectral resolutions are poor. In the second group of sequences, echo planar imaging acquisition is repeated for every phase-encode gradient step to improve upon the spatial resolution and signal-to-noise ratio at the expense of acquisition time. Here we report a novel combination of these two groups of sequences aimed at providing additional flexibility in trade-offs between the spectral bandwidth, signal-to-noise ratio, spatial resolution and imaging time. Preliminary results for both chemical shift imaging and three-dimensional spatial imaging are presented. The chemical shift imaging was optimized for excitation of the N-acetyl aspartate (NAA). An interesting consequence of our approach is that the Nyquist ghost is transferred from the spectrum to the metabolite image.