A robust multi-shot scan strategy for high-resolution diffusion weighted MRI enabled by multiplexed sensitivity-encoding (MUSE)

Abstract

Diffusion weighted magnetic resonance imaging (DWI) data have been mostly acquired with single-shot echo-planar imaging (EPI) to minimize motion induced artifacts. The spatial resolution, however, is inherently limited in single-shot EPI, even when the parallel imaging (usually at an acceleration factor of 2) is incorporated. Multi-shot acquisition strategies could potentially achieve higher spatial resolution and fidelity, but they are generally susceptible to motion-induced phase errors among excitations that are exacerbated by diffusion sensitizing gradients, rendering the reconstructed images unusable. It has been shown that shot-to-shot phase variations may be corrected using navigator echoes, but at the cost of imaging throughput. To address these challenges, a novel and robust multi-shot DWI technique, termed multiplexed sensitivity-encoding (MUSE), is developed here to reliably and inherently correct nonlinear shot-to-shot phase variations without the use of navigator echoes. The performance of the MUSE technique is confirmed experimentally in healthy adult volunteers on 3Tesla MRI systems. This newly developed technique should prove highly valuable for mapping brain structures and connectivities at high spatial resolution for neuroscience studies.

Figure 1

(a): Four-shot interleaved DTI data ( $\text{b}=500\frac{\mathit{sec}}{{mm}^2}$) of 15-direction are susceptible to motion-induced phase errors. (b): Using the MUSE technique, the motion-induced aliasing artifacts can be eliminated. (c): The FA map generated from the conventional SENSE reconstruction has a low SNR. (d): The SNR is improved in FA map produced with the MUSE technique.

Figure 2

(a): Pronounced motion-induced artifacts appear in interleaved DTI when there exist local and nonlinear motions (e.g., in the brainstem). (b): The aliasing artifact can be eliminated with the MUSE technique. (c): The SNR is low in the FA map produced with the conventional SENSE procedure. (d): Using the MUSE technique, the FA map of high-SNR can be achieved.

Figure 3

(a): DWI data of high in-plane resolution (voxel size: 0.375 × 0.375 × 5mm³; $\text{b}=800\frac{\mathit{sec}}{{mm}^2}$) provides good anatomic resolvability. (b): The low-resolution reconstruction of the same data set (voxel size: 1.5 × 1.5 × 5mm³) cannot reveal the same anatomic details.

Figure 4

(a): FA map of high in-plane resolution (voxel size: 0.3 × 0.3 × 8mm³; $\text{b}=500\frac{\mathit{sec}}{{mm}^2}$). (b): FA values for voxels inside the white box of (a). (c) The contour of the indicated green and red voxels in (b) overlaid onto the mean DWI image. (d) The contour of the indicated green and red voxels in (b) overlaid onto the baseline T2-weighted EPI.

Figure 5

(a): MUSE-generated DWI corresponding to different b factors (from $500\text{to}2000\frac{\mathit{sec}}{{mm}^2}$ in a $250\frac{\mathit{sec}}{{mm}^2}$ step). (b): SENSE-generated images of the corresponding b factors (from $500\text{to}2000\frac{\mathit{sec}}{{mm}^2}$). (c): The magnitude average of all 7 MUSE-generated DWI. (d): The magnitude average of all 7 SENSE-generated DWI. (e) The coefficient of variation measured from white-matter ROIs of MUSE-DWI (black bars) and SENSE-DWI (yellow bars) corresponding to different b factors.