Improved Luminal Visualization of Flow Diverters after Deployment Using Non-Contrast-Enhanced 3D-TOF-MRA: A Comparison between the Flow-Redirection Endoluminal Device and the Pipeline Flex Embolization Device with Shield Technology

Objective: This study aimed to improve the accuracy of luminal evaluation of flow diverters (FDs) using non-contrast-enhanced 3D time-of-flight MRA (3D-TOF-MRA). Methods: The Flow-Redirection Endoluminal Device (FRED) and Pipeline Flex Embolization Device with Shield Technology (Pipeline) were deployed in phantom vessels with an inner diameter of 4 mm, and a phantom vessel without an FD was used as the reference. A diluted Gd contrast agent, adjusted to achieve a T1 relaxation time equivalent to that of blood, was circulated through the phantom vessels under steady flow conditions. Non-contrast-enhanced 3D-TOF-MRA images were acquired with varying echo time (TE), flip angle (FA), and Tilted Optimized Non-Saturating Excitation (TONE) ramp settings. Source images obtained from the central and edge regions of the stents were used to evaluate the relative in-stent signal (RIS) and lumen area ratio. In addition, the signal difference between the inflow and outflow regions was calculated and assessed as the saturation ratio. Results: RIS values for both FRED and Pipeline decreased with increasing TE at both the central and edge regions. A similar decreasing trend was observed for the area ratio. Overall, FRED demonstrated relatively higher RIS and area ratio values than Pipeline. Regarding the FA variation, the peak RIS at the center regions occurred at an FA of 35° for both FDs, followed by a plateau. In the TONE ramp analysis, a setting of 30% yielded a saturation ratio closest to 100%. Conclusion: These findings suggest that luminal visualization of FDs can be improved by optimizing 3D-TOF-MRA acquisition parameters, particularly the TE, FA, and TONE ramp settings.