Fractional Flow on TOF-MRA as a Measure of Stroke Risk in Children with Intracranial Arterial Stenosis

Abstract

Background and purpose: Conventional angiography is the criterion standard for measuring intracranial arterial stenosis. We evaluated signal intensity ratios from TOF-MRA as a measure of intracranial stenosis and infarct risk in pediatric stroke.

Materials and methods: A retrospective study was undertaken in children with intracranial arterial stenosis, who had TOF-MRA and conventional angiography performed within 6 months. Arterial diameters were measured for percentage stenosis. ROI analysis on TOF-MRA measured signal intensity in pre- and poststenotic segments, with post-/pre-signal intensity ratios calculated. The Pearson correlation was used to compare percentage stenosis on MRA with conventional angiography and signal intensity ratios with percentage stenosis; the point-biserial correlation was used for infarcts compared with percentage stenosis and signal intensity ratios. Sensitivity, specificity, and positive and negative predictive values were calculated for determining severe (≥70%) stenosis from MRA and signal intensity ratios against the criterion standard conventional angiography. P < .05 was considered statistically significant.

Results: Seventy stenotic segments were found in 48 studies in 41 children (median age, 11.0 years; range, 5 months to 17.0 years; male/female ratio, 22:19): 20/41 (48.8%) bilateral, 11/41 (26.8%) right, and 10/41 (24.4%) left, with the most common site being the proximal middle cerebral artery (22/70, 31%). Moyamoya disease accounted for 27/41 (65.9%). Signal intensity ratios and conventional angiography stenosis showed a moderate negative correlation (R = -0.54, P < .001). Receiver operating characteristic statistics showed an area under the curve of 0.86 for using post-/pre-signal intensity ratios to determine severe (≥70%) carotid stenosis, yielding a threshold of 1.00. Sensitivity, specificity, and positive and negative predictive values for severe stenosis were the following-MRA: 42.8%, 58.8%, 30.0%, and 71.4%; signal intensity ratio >1.00: 97.1%, 77.8%, 71.7%, and 97.4%; combination: 75.5%, 100%, 100%, and 76.8%, respectively. Signal intensity ratios decreased with increasing grade of stenosis (none/mild-moderate/severe/complete, P < .001) and were less when associated with infarcts (0.81 ± 0.52 for arteries associated with downstream infarcts versus 1.31 ± 0.55 for arteries without associated infarcts, P < .001).

Conclusions: Signal intensity ratios from TOF-MRA can serve as a noninvasive measure of intracranial arterial stenosis and allow identification of high-risk lesions in pediatric stroke.