Time-Resolved 3D Contrast-Enhanced MRA on 3.0T: a Non-Invasive Follow-Up Technique after Stent-Assisted Coil Embolization of the Intracranial Aneurysm

OBJECTIVE: To evaluate the usefulness of time-resolved contrast enhanced magnetic resonance angiography (4D MRA) after stent-assisted coil embolization by comparing it with time of flight (TOF)-MRA. MATERIALS AND METHODS: TOF-MRA and 4D MRA were obtained by 3T MRI in 26 patients treated with stent-assisted coil embolization (Enterprise:Neuroform = 7:19). The qualities of the MRA were rated on a graded scale of 0 to 4. We classified completeness of endovascular treatment into three categories. The degree of quality of visualization of the stented artery was compared between TOF and 4D MRA by the Wilcoxon signed rank test. We used the Mann-Whitney U test for comparing the quality of the visualization of the stented artery according to the stent type in each MRA method. RESULTS: The quality in terms of the visualization of the stented arteries in 4D MRA was significantly superior to that in 3D TOF-MRA, regardless of type of the stent (p < 0.001). The quality of the arteries which were stented with Neuroform was superior to that of the arteries stented with Enterprise in 3D TOF (p < 0.001) and 4D MRA (p = 0.008), respectively. CONCLUSION: 4D MRA provides a higher quality view of the stented parent arteries when compared with TOF.

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

PURPOSE: The 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 METHODS: Four stents (Neuroform, Wingspan, Solitaire, and Enterprise) were placed in a vascular flow phantom and imaged by changing flip angle (FA; 20degrees,30degrees,40degrees,50degrees and 60degrees) 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. RESULTS: The 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 20degrees/31 KHz (Neuroform), 20degrees/31 KHz and 30degrees/42 KHz (Wingspan), 40degrees/42 KHz and 50degrees/31 KHz (Solitaire) and 40degrees/31 KHz and 50degrees/31 KHz (Enterprise). Among these MIP images with significantly high RIS, images with FA/BW value of 20degrees/31 KHz (Neuroform and Wingspan) and 50degrees/31 KHz (Solitaire and Enterprise) had the best image quality. CONCLUSION: The 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.