High resolution diffusion‐weighted imaging using readout‐segmented echo‐planar imaging, parallel imaging and a two‐dimensional navigator‐based reacquisition

TLDR

Single‑shot EPI is the standard for diffusion MRI because of its low motion sensitivity, yet it suffers from susceptibility‑induced artifacts and limited resolution, and even parallel imaging such as GRAPPA only partially mitigates these problems at higher field strengths like 3 T. This study investigates whether combining readout‑segmented EPI with parallel imaging can produce high‑resolution diffusion images at 1.5 T and 3 T while markedly reducing susceptibility artifacts compared with single‑shot EPI. The method employs a 2‑D navigator to perform nonlinear phase correction and to trigger real‑time reacquisition of data that cannot be corrected. Volunteer scans demonstrate that the approach robustly corrects motion‑induced phase artifacts and yields scan times compatible with routine clinical use.

Abstract

Single-shot echo-planar imaging (EPI) is well established as the method of choice for clinical, diffusion-weighted imaging with MRI because of its low sensitivity to the motion-induced phase errors that occur during diffusion sensitization of the MR signal. However, the method is prone to artifacts due to susceptibility changes at tissue interfaces and has a limited spatial resolution. The introduction of parallel imaging techniques, such as GRAPPA (GeneRalized Autocalibrating Partially Parallel Acquisitions), has reduced these problems, but there are still significant limitations, particularly at higher field strengths, such as 3 Tesla (T), which are increasingly being used for routine clinical imaging. This study describes how the combination of readout-segmented EPI and parallel imaging can be used to address these issues by generating high-resolution, diffusion-weighted images at 1.5T and 3T with a significant reduction in susceptibility artifact compared with the single-shot case. The technique uses data from a 2D navigator acquisition to perform a nonlinear phase correction and to control the real-time reacquisition of unusable data that cannot be corrected. Measurements on healthy volunteers demonstrate that this approach provides a robust correction for motion-induced phase artifact and allows scan times that are suitable for routine clinical application.