Optimization of MR Parameters of 3D TOF-MRA for Various Intracranial Stents at 3.0T MRI

Abstract

PurposeThe in-stent signal reduction of the stented artery caused by susceptibility artifact or radiofrequency shielding artifact limited the use of time-of-flight MR angiography (TOF-MRA) as a follow-up tool after intracranial stenting. We showed the degree of an artifact according to different stent types, and optimized MR parameters for TOF-MRA in patients with intracranial stent on 3.0 T MRI.Materials and MethodsFour stents (Neuroform, Wingspan, Solitaire, and Enterprise) were placed in a vascular flow phantom and imaged by changing flip angle (FA; 20°,30°,40°,50° and 60°) and bandwidth (BW; 31, 42 and 62.5 KHz) using TOF-MRA. Source data of each image set with different FA and BW were reconstructed with the maximal intensity projection (MIP) technique, and MIP images were used to evaluate the in-stent signal reduction of each stent according to the change of MR parameters. The in-stent signal reduction was assessed by calculating the relative in-stent signal (RIS) inside the stent as compared with background and signal intensity of the tube outside the stent. The optimal FA and BW of each stent were determined by comparing the RIS in each stent by one-sample t test. Finally, one neuroradiologist chose one image set with the best image quality.ResultsThe mean RIS for Neuroform, Wingspan, Solitaire and Enterprise stent was 66.3 ± 6.0, 44.2 ± 5.8, 22.8 ± 3.3 and 8.2 ± 2.9, respectively. The significantly high RIS of each stent was obtained with FA/BW value of 20°/31 KHz (Neuroform), 20°/31 KHz and 30°/42 KHz (Wingspan), 40°/42 KHz and 50°/31 KHz (Solitaire) and 40°/31 KHz and 50°/31 KHz (Enterprise). Among these MIP images with significantly high RIS, images with FA/BW value of 20°/31 KHz (Neuroform and Wingspan) and 50°/31 KHz (Solitaire and Enterprise) had the best image quality.ConclusionThe degree of artifact was variable according to the design of each intracranial stent. The luminal visualization of closed-cell design stents such as Solitaire and Enterprise can be improved by higher FA. Thus, MR parameter should be adjusted according to the type of intracranial stents.

Assessing Blood Flow in an Intracranial Stent: A Feasibility Study of MR Angiography Using a Silent Scan after Stent-Assisted Coil Embolization for Anterior Circulation Aneurysms

“…Future studies are required to examine open-cell-design stents because the stent form might produce differences in the MRA images. 19 These study results may only be preliminary due to the small number of cases examined, limited to the anterior circulation and only 1 stent design. For potential replacement of TOF or contrastenhanced MRA for aneurysm follow-up imaging after treatment, one must analyze not only in-stent flow but also aneurysm occlusion status.…”

Fate of Coiled Aneurysms with Minor Recanalization at 6 Months: Rate of Progression to Further Recanalization and Related Risk Factors

“…Although, TOF MRA can be helpful in estimating the degree of recanalization, stent artifacts obscuring minor recanalization could occur. [27][28][29][30] Moreover, the mean aneurysm size in our subjects was estimated at 6.3 Ϯ 3.2 mm. In Korea, coiled aneurysms Յ10 mm account for 89.3% of lesions in a national cohort of unruptured aneurysms.…”

Usefulness of Non–Contrast-Enhanced MR Angiography Using a Silent Scan for Follow-Up after Y-Configuration Stent-Assisted Coil Embolization for Basilar Tip Aneurysms

“…Neuroform and Enterprise stents are nitinol stents. 12,16,17,23 The Neuroform stent has an open-cell design (ie, stent-strut is not interconnected). On the other hand, the Enterprise stent has a closed-cell design (ie, stent-strut is interconnected).…”