Arterial spin labeling detects trapped labeled spins in flow-diverted aneurysms and it reflects intra-aneurysmal flow stasis

Abstract

Background: This study evaluated arterial spin labeling (ASL) imaging findings in flow-diverted aneurysms (FD-ANs).

Methods: Twenty-one patients with internal carotid artery aneurysms treated with flow-diverter stent (FDS) were included. Time-of-flight magnetic resonance angiography (TOF-MRA) and ASL were performed before and after follow-up digital subtraction angiography (DSA) on the day, 6 months, and/or 1 year after treatment. Two radiologists rated the clarity of the depiction of FD-ANs for MRA on a 3-point scale and the ASL signal intensity of the aneurysm as negative or positive. A neurosurgeon assessed DSA findings using the O'Kelly-Marotta (OKM) grading scale, categorizing them into filling and stasis grades. The 23 examinations were classified according to the OKM grading scale, and the proportion of ASL-positive cases and the proportion of cases with MRA scores of 1-2 (detectable) were calculated for each grade. The relationship between the OKM grading scale and ASL positivity or MRA detectable was examined using Fisher's exact test.

Results: Of seven examinations where the statis grade was 1 or 2, no examinations showed ASL positivity. However, among the 16 examinations in which the stasis grade was 3, 9 examinations showed ASL positivity. A significant association was observed between stasis grade and ASL positivity (p = 0.035). In contrast, no significant relationship was observed between the OKM grading scale and the MRA 3-point scale.

Conclusion: High-signal ASL in FD-ANs could reflect stasis within the aneurysm; therefore, noninvasive ASL can indicate reduction in intra-aneurysmal blood flow after treatment and reperfusion during posttreatment observation.

Keywords: Aneurysm; endovascular procedures; magnetic resonance angiography; perfusion magnetic resonance imaging.

Figure 1.

Case 3-1, 71-year-old female. In the pre-flow-diverter stent treatment rotational digital subtraction angiography (DSA) volume rendering image, an aneurysm with a maximum diameter of 16 mm and a neck length of 8 mm protruding posteriorly from C4 is observed (a). Compared with the pretreatment DSA lateral image (b), the entire aneurysm is depicted in the arterial phase of the immediate posttreatment DSA (not shown); however, contrast agent is stagnant in some parts until the venous phase (c), and the O'Kelly–Marotta grading scale is A3. On MRI, the entire aneurysm is depicted on MRA immediately before treatment (d); however, immediately after treatment, a signal is observed only in the lateral part, and it is judged as 1 point on the MRA 3-point scale (e). In contrast, in ASL, a signal clearly stronger than the cortex is confirmed around the right cavernous sinus, and it is judged as positive (f).

Figure 2.

Case 13-1, 47-year-old female. In the pre-flow-diverter stent treatment rotational digital subtraction angiography (DSA) volume rendering image, an aneurysm with a maximum diameter of 5 mm and a neck length of 4 mm protruding anteriorly from C2 is observed (a). Compared with the pretreatment DSA lateral image (b), the entire aneurysm is depicted in the arterial phase of the immediate posttreatment DSA (not shown); however, all contrast agent is completely cleared in the capillary phase (c), and the O'Kelly–Marotta grading scale is A2. On MRI, the entire aneurysm is depicted on MRA immediately before treatment (d), and even immediately after treatment, there is a signal throughout the entire aneurysm, and it is judged as 2 points on the MRA 3-point scale (e). In contrast, in ASL, no difference in signal between the left and right is observed, and it is judged as negative (f).

Figure 3.

Case 2-3, 77-year-old female. In the pre-flow-diverter stent treatment rotational digital subtraction angiography (DSA) volume rendering image, an aneurysm with a maximum diameter of 23 mm and a neck length of 7 mm irregularly protruding from C3 is observed (a). Compared with the pretreatment DSA lateral image (b), only a part of the neck is depicted in the arterial phase of the follow-up DSA 1 year after treatment (not shown); however, the contrast agent is stagnant in some parts until the venous phase (c), and the O'Kelly–Marotta grading scale is C3. On MRI, the entire aneurysm is depicted on MRA immediately before treatment (d); however, on the follow-up MRA 1 year after treatment, no signal is observed only in the aneurysm, and it is judged as 0 points on the MRA 3-point scale (e). In contrast, in ASL, a signal clearly stronger than the cortex is confirmed around the right cavernous sinus, and it is judged as positive (f).