Noninvasive Fractional Flow on MRA Predicts Stroke Risk of Intracranial Stenosis

Abstract

BACKGROUND AND PURPOSE: Fractional flow may identify hemodynamic effects and ischemic risk beyond percent stenosis of an artery. We hypothesized that diminished TOF-MRA signal intensity distal to an intracranial stenosis predicts stroke risk. METHODS: TOF-MRA was acquired prospectively in the SONIA-WASID trials. The distal/proximal signal intensity ratio (SIR) was calculated from 3 mm regions of interest, blinded to outcome. Univariate and multivariate analyses included clinical variables, SIR, and invasive angiography measures to identify predictors for risk of stroke in the territory. RESULTS: 189 patients with 50-99% symptomatic intracranial stenosis in SONIA-WASID had TOF-MRA available. In univariate analysis, the hazard ratio (HR) for stroke in the territory of the symptomatic artery with SIR < .9 was 5.2 (1.8, 15.3; P < .001) as compared to SIR ≥ .9. Multivariate analysis correcting for baseline systolic blood pressure, LDL, centrally measured percent stenosis, recency of symptoms, TICI and downstream collaterals, the HR for SIR < .9 was 10.9 (2.0, 58.9; P < .001). In those with <70% stenosis, a SIR < .9 maintained a significant association with recurrent stroke in the territory (P = .006), with a 2-year event rate of 17.3%. CONCLUSIONS: Fractional flow assessed by TOF-MRA SIR may be a useful noninvasive tool to identify high-risk intracranial lesions. CLINICAL TRIAL REGISTRATION-URL: This trial was not registered because enrollment began prior to July 1, 2005.