Reduction of Aliasing Artifacts in Diffusion-Weighted PROPELLER Imaging

Introduction Diffusion imaging is typically performed in axial planes. This is largely due to its reliance on single-shot echo-planar imaging (EPI) which suffers from increased image distortion in sagittal and coronal planes because of concomitant gradient fields [1-2], especially with strong gradients and/or at relatively low B0-fields (including 1.5T). Diffusion-weighted (DW) imaging in non-axial planes is preferred in some applications (e.g., visualization of corticospinal tracts using DTI), but has been hindered by EPI-based acquisitions. Recently, FSE-based PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) diffusion sequences have been developed as an alternative to EPI [3-5], opening the possibility to perform diffusion imaging in sagittal or coronal planes. In PROPELLER sampling, however, the phase-encoding axis is not fixed to a specific direction. When the phase-encoding direction is rotated to the superior/inferior direction in sagittal or coronal planes, aliasing can occur in some blades, producing non-localized streaking artifacts across the image. We describe a “slice tilting” technique to reduce the streaking artifacts in PROPELLER imaging and demonstrate the feasibility of using this technique to obtain DW images in sagittal and coronal planes with improved image quality.