A Simple Acquisition Strategy to Avoid Off-Resonance Blurring in Spiral Imaging with Redundant Spiral-In/Out k-Space Trajectories

PurposeThe major hurdle to widespread adoption of spiral trajectories has been their poor off-resonance performance. Here we present a self-correcting spiral k-space trajectory that avoids much of the well-known spiral blurring during data acquisition. Theory and MethodsIn comparison with a traditional spiral-out trajectory, the spiral-in/out trajectory has improved off-resonance performance. By combining two spiral-in/out acquisitions, one rotated 180 degrees in k-space compared with the other, multishot spiral-in/out artifacts are eliminated. A phantom was scanned with the center frequency manually tuned 20, 40, 80, and 160 Hz off-resonance with both a spiral-out gradient echo sequence and the redundant spiral-in/out sequence. The phantom was also imaged in an oblique orientation in order to demonstrate improved concomitant gradient field performance of the sequence. Additionally, the trajectory was incorporated into a spiral turbo spin echo sequence for brain imaging. ResultsPhantom studies with manually tuned off-resonance agree well with theoretical calculations, showing that moderate off-resonance is well-corrected by this acquisition scheme. Blur due to concomitant fields is reduced, and good results are obtained in vivo. ConclusionThe redundant spiral-in/out trajectory results in less image blur for a given readout length than a traditional spiral-out scan, reducing the need for complex off-resonance correction algorithms. Magn Reson Med 73:704-710, 2015. (c) 2014 Wiley Periodicals, Inc.