3D T2-Weighted Sampling Perfection with Application-Optimized Contrasts Using Different Flip Angle Evolutions (SPACE) and 3D Time-of-Flight (TOF) MR Angiography Fusion Imaging for Occluded Intracranial Arteries

Abstract

Objective: Determining the course of occluded vessels in advance will increase the success rate and safety of mechanical thrombectomy (MT). Herein, we evaluate the usefulness of MR fusion images created via 3D T2-weighted sampling perfection with application-optimized contrasts using different flip angle evolutions (T2-SPACE) and 3D time-of-flight (TOF)-MRA for visualization of occluded vessels in patients with acute ischemic stroke (AIS) before MT.

Methods: We enrolled 26 patients with AIS caused by intracranial large vessel occlusion who presented at our hospital and underwent MRI with fusion images unaffected by motion artifacts in our study. All patients underwent T2-SPACE and TOF-MRA followed by MT. We created fusion images of the T2-SPACE and TOF-MRA by combining a translucent image of the occluded artery produced by the flow void effect in T2-SPACE with the same vessel in a TOF-MRA image. Fusion images were compared with post-recanalization angiography and post-recanalization MRA, respectively, and the degree of agreement in depiction of M1 runs and M2 branching beyond the occlusion on three levels was assessed. Imaging evaluations were performed independently by two endovascular specialists.

Results: The interobserver agreement of the MRI findings about the concordance of the occluded vessel's run was excellent (kappa was 0.87 [confidence interval: 0.61-1.12]). In all, 21 patients (80.8%) had excellent imaging, four (15.4%) had fair imaging, and one (3.8%) had a divided opinion of the rating between excellent and fair imaging. No cases were judged to be poorly drawn. Even if there was a localized signal loss, its distal portion could be delineated, so it did not affect the estimation of the entire vessel run, and we found that the anatomical structures of the occluded vessels were distinctly visible in the fusion images.

Conclusion: We demonstrated that MR fusion images derived using T2-SPACE and MRA methodologies could determine the courses of occluded vessels prior to MT performed for AIS. Fusion MR imaging may have potential as a preoperative test for ensuring effective and safe MT procedures.

Keywords: T2-weighted sampling perfection with application-optimized contrasts using different flip angle evolutions; acute ischemic stroke; intracranial artery occlusion; magnetic resonance imaging; mechanical thrombectomy.

Fig. 1. Detection of blood vessels beyond the occluded sites in the left internal carotid artery occlusion case. This figure depicts images obtained in Case 1, with the occlusion point defined as the left ICA. Original 3D TOF-MRA images obtained at admission do not delineate the course of the MCA distal to the ICA (A). Angiography performed prior to MT (B) demonstrates a similar appearance as compared with 3D TOF-MRA at admission (A). Fusion images obtained from 3D T2-weighted SPACE and 3D TOF-MRA reveal the course of the MCA distal to the occlusion (C). The ICA in the petrous bone was difficult to delineate, but the intracranial MCA was well delineated, M1 showed a large run caudally, and the ensuing M2 was open vertically. Therefore, the image delineation was rated “excellent.” MRA images (D) and angiography (E) acquired after MT match the fusion MR images (C) in terms of visualizing the MCA distal to the occlusion. Double arrows and arrowheads indicate the same point in the vessels. ICA: internal carotid artery; MCA: middle cerebral artery; MT: mechanical thrombectomy; SPACE: sampling perfection with application-optimized contrasts using different flip angle evolutions; TOF: time-of-flight

Fig. 2. Detection of blood vessels beyond the occluded sites in the right MCA M1 distal segment occlusion case. This figure depicts images obtained in Case 2, with the occlusion point defined as the right MCA M1 distal segment. Original 3D TOF-MRA images obtained at admission do not delineate the course of the MCA distal to the occlusion site (A: white arrowhead). Angiography performed prior to MT (B) demonstrates a similar appearance as compared with 3D TOF-MRA at admission (A). Fusion images obtained from 3D T2-weighted SPACE and 3D TOF-MRA reveal the course of the MCA distal to the occlusion (C: white double arrows). This case was a monofurcation branching type, and M1–M2 exhibited a steep branching angle. The image delineation was rated “excellent.” MRA images (D) and angiography (E) acquired after MT match the fusion MR images (C) in terms of visualizing the MCA distal to the occlusion. Double arrows and arrowheads indicate the same point in the vessels. MCA: middle cerebral artery; MT: mechanical thrombectomy; SPACE: sampling perfection with application-optimized contrasts using different flip angle evolutions; TOF: time-of-flight

Fig. 3. Detection of blood vessels beyond the occluded sites in the right MCA M2 segment occlusion case. This figure depicts images obtained in Case 3, with the occlusion point defined as the right MCA M2 segment. Original 3D TOF-MRA images obtained at admission do not delineate the course of the MCA distal to the occlusion site (A: white arrowhead). Angiography performed prior to MT (B) demonstrates a similar appearance as compared with 3D TOF-MRA at admission (A). Fusion images obtained from 3D T2-weighted SPACE and 3D TOF-MRA reveal the course of the MCA distal to the occlusion (C: white double arrows). M2 runs linear, but part of the run is missing in the fusion image. Therefore, the image delineation was rated “fair.” MRA images (D) and angiography (E) acquired after MT match the fusion MR images (C) in terms of visualizing the MCA distal to the occlusion. In the original MRA image before MT (F), the occluded vessels were not shown, but depicted as low signal in original T2-SPACE (G), and part of the occlusion was high signal internally (G: arrowhead). The original MRA after MT (H) showed no particular abnormality in the vascular signal of the occlusion site (H: arrowhead). Double arrows and arrowheads indicate the same point in the vessels. MCA: middle cerebral artery; MT: mechanical thrombectomy; SPACE: sampling perfection with application-optimized contrasts using different flip angle evolutions; TOF: time-of-flight