Effects of Imaging Parameters on the Quality of Contrast-Enhanced MR Angiography of Cerebral Aneurysms Treated Using Stent-Assisted Coiling: A Phantom Study

Abstract

Purpose:To quantitatively investigate in vitro the effects of flip angle (FA), receiver bandwidth (BW), echo time (TE), and magnetic field strength (FS) on image noise and artifacts induced by stent-assisted coiling on contrast-enhanced MR angiography (CE-MRA) images, as a first step towards optimization of imaging parameters.Methods:A phantom simulating a cerebral aneurysm treated using stent-assisted coiling was filled with diluted gadolinium contrast medium, and MR angiography were obtained using varied parameters: FA (10°–60°), BW (164–780 Hz/pixel), and FS (1.5 and 3.0T). The TE varied automatically with BW because the TE was set to the smallest value. Three kinds of indices were semi-automatically calculated to quantify the severity of stent- and coil-induced artifacts: artificial lumen narrowing (ALN) representing a decrease in the in-stent luminal area, and relative in-stent signal (RISS) and relative in-coil signal (RISC) representing an increase in the in-stent and in-coil signal intensities, respectively. We also measured the ratio of in-stent signal to noise (IS/N) for each parameter. The variation in these indices with variations in FA, BW (TE), and FS was analyzed.Results:An increase in FA led to an increase of up to 65% in the RISS, while the IS/N increased by up to three times. The 1.5T scanner indicated fewer artifacts (71% lower ALN, two times higher RISS, and 40% higher RISC) than the 3.0T scanner. On the other hand, the 1.5T scanner worsened the IS/N compared with the 3.0T scanner, although the difference was relatively small. Variation in BW (and hence, TE) led to a trade-off between artifact severity and IS/N.Conclusion:A high FA and low FS should be used for improved artifact severity and IS/N on CE-MRA images of a stent-assisted coil. A wide BW (short TE) could improve artifact severity at the expense of the image noise.

Non-Contrast-Enhanced Silent Scan MR Angiography of Intracranial Anterior Circulation Aneurysms Treated with a Low-Profile Visualized Intraluminal Support Device

“…Choi et al 8 reported that a short TE could increase signal intensity while optimizing the stent-visualization parameter. Similarly, Yamada et al 22 reported that a TE of 1.54 -1.60 ms was used in their 3D TOF-MRA study, and Ikushima et al 23 reported that a wide bandwidth (short TE) could increase the in-stent signal intensity and in-coil signal intensity during a CE-MRA phantom study. Furthermore, Irie et al 15 reported a TE of 0.016 ms during Silent MRA.…”

Investigating Signal Loss due to a Carotid Artery Stent in 3D-TOF-MRA

“…As mentioned in the introduction, there are two kinds of artifacts induced by a stent, one is the magnetic susceptibility artifact and the other is the RF-shielding artifact. It is also reported that wide Bw and short TE are effective in suppressing magnetic susceptibility artifacts, 10 but this is the case of setting to automatically minimize TE. In our study, according to a phantom experiment in which Bw and TE were independently changed, RIS stent was reduced by shortening TE, but there was no correlation with Bw.…”

Usefulness of contrast-enhanced and TOF MR angiography for follow-up after low-profile stent-assisted coil embolization of intracranial aneurysms

“…The extent of signal loss changes, depending upon thickness of the stent strut, cell design of the stent, stent material, diameter of the stent, tortuosity of parent artery, orientation of the stent, and MRI parameters. 10,11,[21][22][23] Open-cell design, thinner stent strut, and nitinol stents are associated with less artifacts and signal loss. 6,24 Smaller voxel, shorter TE, shorter TR, wider bandwidth, and a parallel imaging technique reduce magnetic susceptibility artifacts.…”

“…6,24 Smaller voxel, shorter TE, shorter TR, wider bandwidth, and a parallel imaging technique reduce magnetic susceptibility artifacts. 21,22,25 The radiofrequency (RF) shielding effect of the stent is decreased by a high FA. 22 In this study, longer TR, longer TE, and narrower bandwidth of TOF MRA were the reasons for increased susceptibility.…”

“…21,22,25 The radiofrequency (RF) shielding effect of the stent is decreased by a high FA. 22 In this study, longer TR, longer TE, and narrower bandwidth of TOF MRA were the reasons for increased susceptibility. The lower FA of TOF MRA increased the RF shielding effect of the stent.…”