Improving Diffusion-Weighted Imaging at 7 Tesla: Reducing Eddy Current Artifacts With Dummy Gradients and Optimized Navigator Echoes
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Purpose: This study proposes a novel method to reduce N/2 ghosting artifacts and eddy current-induced image shifts in single-shot diffusion-weighted echo-planar imaging (DW-EPI) for 7 tesla (T) MRI. This method integrates dummy diffusion gradients and optimized navigator echo placement to improve phase correction and artifact reduction, addressing the limitations of conventional phase correction methods. Materials and Methods: The proposed method was compared to the conventional approach, which uses Nav1 for phase correction without dummy diffusion gradients. The new approach incorporates Nav2 for phase correction and dummy diffusion gradients to mitigate eddy current effects. Phantom and in vivo experiments were conducted to evaluate the N/2 ghosting intensity, phase stability, and geometric accuracy. In vivo diffusion- weighted images were acquired at b = 1000 s/mm2 and the effectiveness of the phase correction was qualitatively and quantitatively assessed. Results: Phase evolution analysis revealed that Nav2 more accurately captures diffusion gradient-induced phase perturbations compared to Nav1, leading to improved N/2 ghosting artifact correction. Phantom experiments demonstrated a 41% reduction in N/2 ghosting artifacts using Nav2 compared to Nav1, confirming its superior phase correction capabilities. The in vivo results showed that the proposed method reduced ghosting artifacts and image shifts, leading to an improved alignment of diffusion-weighted images with the reference b = 0 image. Furthermore, the inclusion of dummy diffusion gradients further reduced eddy current-induced artifacts, enhancing image stability and tissue contrast in high-field diffusion-weighted imaging. Conclusion: The proposed method of integrating Nav2 for phase correction and dummy diffusion gradients significantly reduced N/2 ghosting artifacts and geometric distortions in high-field diffusion MRI. These findings suggest that optimizing navigator positioning and incorporating dummy diffusion gradients can enhance the phase stability and improve the reliability of DW-EPI at 7 T. However, as this was a preliminary study with a limited in vivo dataset (n = 2), further validation with larger datasets, different MRI systems, and broader imaging conditions is necessary to fully assess its robustness and clinical applicability.
Abstract
Purpose: This study proposes a novel method to reduce N/2 ghosting artifacts and eddy current-induced image shifts in single-shot diffusion-weighted echo-planar imaging (DW-EPI) for 7 tesla (T) MRI. This method integrates dummy diffusion gradients and optimized navigator echo placement to improve phase correction and artifact reduction, addressing the limitations of conventional phase correction methods. Materials and Methods: The proposed method was compared to the conventional approach, which uses Nav1 for phase correction without dummy diffusion gradients. The new approach incorporates Nav2 for phase correction and dummy diffusion gradients to mitigate eddy current effects. Phantom and in vivo experiments were conducted to evaluate the N/2 ghosting intensity, phase stability, and geometric accuracy. In vivo diffusion- weighted images were acquired at b = 1000 s/mm2 and the effectiveness of the phase correction was qualitatively and quantitatively assessed. Results: Phase evolution analysis revealed that Nav2 more accurately captures diffusion gradient-induced phase perturbations compared to Nav1, leading to improved N/2 ghosting artifact correction. Phantom experiments demonstrated a 41% reduction in N/2 ghosting artifacts using Nav2 compared to Nav1, confirming its superior phase correction capabilities. The in vivo results showed that the proposed method reduced ghosting artifacts and image shifts, leading to an improved alignment of diffusion-weighted images with the reference b = 0 image. Furthermore, the inclusion of dummy diffusion gradients further reduced eddy current-induced artifacts, enhancing image stability and tissue contrast in high-field diffusion-weighted imaging. Conclusion: The proposed method of integrating Nav2 for phase correction and dummy diffusion gradients significantly reduced N/2 ghosting artifacts and geometric distortions in high-field diffusion MRI. These findings suggest that optimizing navigator positioning and incorporating dummy diffusion gradients can enhance the phase stability and improve the reliability of DW-EPI at 7 T. However, as this was a preliminary study with a limited in vivo dataset (n = 2), further validation with larger datasets, different MRI systems, and broader imaging conditions is necessary to fully assess its robustness and clinical applicability.