READOUT MOSAIC SEGMENTED DW EPI WITH PARALLEL IMAGING AND RPGM

Stanford University, Stanford CA

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Readout Mosaic Segmented DW EPI with parallel imaging and RPGM Samantha Holdsworth, Stefan Skare, Anders Nordell, Rexford Newbould, Roland Bammer The objective of this work is to improve the distortion characteristics and spatial resolution of conventional diffusion weighted EPI images. The distortions in EPI are mainly determined by the slow traversal through k-space along the phase encode direction which gives rise to blurring and geometric distortions. The short-axis propeller EPI scheme has been proposed in the literature as a robust alternative for high resolution diffusion imaging. By accelerating the k-space traversal along the phase encoding direction, distortion artifacts can be significantly diminished. Further reduction of these artifacts can be achieved when this sampling strategy is combined with parallel imaging. Similarly to FSE-Propeller, this technique also has the advantage of being inherently self navigated - whereby the center portion of k-space can be used to extract the navigator information. However, radial sampling requires N/[unreadable] more sampling points for a given target resolution and is thus associated with a scan time penalty. Readout Mosaic Segmentation was suggested as an alternative approach for acquiring high resolution EPI images in a short scan time. With this scheme, multiple segments of k-space are acquired with a break in the readout direction. For each segment, a second EPI readout (or navigator echo) sampled in the central segment of k-space is used to correct for k-space shifts due to the presence of the DWI encoding gradients and physiological motion.