MATERIALS AND METHODS

Seventy-eight large, unruptured internal carotid aneurysms in 78 patients were the subjects of this study. After 6 months of treatment, they underwent follow-up digital subtraction angiography, Silent MRA, and TOF-MRA, performed simultaneously. All images were independently reviewed by 2 neurosurgeons and 1 radiologist and rated on a 4-point scale from 1 (not visible) to 4 (excellent) to evaluate the parent artery. The aneurysmal embolization status was assessed with 2 ratings: complete or incomplete occlusion.

RESULTS

The mean scores of Silent MRA and TOF-MRA regarding the parent artery were 3.18 ± 0.72 and 2.31 ± 0.86, respectively, showing a significantly better score with Silent MRA (P < .01). In the assessment of the embolization of aneurysms on Silent MRA and TOF-MRA compared with DSA, the percentages of agreement were 91.0% and 80.8%, respectively.

CONCLUSIONS

Silent MRA is superior for visualizing blood flow images inside flow-diverter devices compared with TOF-MRA. Furthermore, Silent MRA enables the assessment of aneurysmal embolization status. Silent MRA is useful for assessing the status of large and giant unruptured internal carotid aneurysms after flow-diverter placement.

The advancement of endovascular treatment devices for intracranial aneurysms has been remarkable. In the treatment of large and giant intracranial aneurysms, a flow-diverter device with a high metal coverage ratio is placed in the parent artery so that it decreases blood flow into aneurysms, promotes thrombosis, and thereby prevents rupture. The usefulness of the flow-diverter device has become apparent by various large-scale studies, and its adoption is consistently increasing.^1–6 However, due to the characteristics of the device, which divert the blood flow and promote thrombosis, careful radiologic follow-up observation is required, and periodic checkups on the status of the aneurysmal embolization and patency of the parent artery are essential. The standard test of follow-up for endovascular treatment of intracranial aneurysms is digital subtraction angiography. Because DSA itself is invasive and involves the risk of complications and adverse effects caused by contrast agents and radiation exposure, less invasive and simple examination procedures are warranted.^7-10 In recent years, the usefulness of contrast-enhanced MR angiography has often been reported,11,12 though using gadolinium carries the risk of serious complications such as nephrogenic systemic fibrosis.¹³ Therefore, time-of-flight MRA has been gaining attention as a viable imaging procedure without having to use a contrast agent.^14,15However, there have been some skeptical views regarding its accuracy.^11,12

We have reported the usefulness of Silent MRA (GE Healthcare, Milwaukee, Wisconsin) as a radiologic follow-up procedure after coil embolization for intracranial aneurysms.^16–18 Silent MRA is a procedure using an ultrashort TE and arterial spin-labeling techniques, which efficiently visualizes the status after the treatment of intracranial aneurysms. In Silent MRA, the 3D image is reconstructed by subtracting the control image from the image obtained by the labeling pulse. At the beginning of its development, although it was a procedure that literally silences the noise of the MR imaging, Silent MRA was attracting attention because its imaging capability after endovascular treatment is superior to that of other modalities. To date, there have been several reports on the comparison of the assessment procedures between TOF-MRA and contrast-enhanced MRA after flow-diverter placement therapy.^12,19,20 To our knowledge, this is the first study of the comparison of Silent MRA and TOF-MRA after flow-diverter placement in intracranial aneurysms, in as much as we searched medical search engines using the key words “Silent MRA,” “TOF-MRA” and “flow diverter.” We report here the posttreatment assessment of flow-diverter therapy by Silent MRA in a study with a population of 78 patients along with the bibliographic consideration of the relevant literature.