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.