Noninvasive fractional flow on MRA predicts stroke risk of intracranial stenosis

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.

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.

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%.

Fractional flow assessed by TOF-MRA SIR may be a useful noninvasive tool to identify high-risk intracranial lesions.

This trial was not registered because enrollment began prior to July 1, 2005.