Background and Aims:
Diagnostic standard in detecting extracranial carotid artery stenosis (ECAS) is contrast-enhanced CT- or MR-Angiography and Doppler ultrasound. This study aims to introduce intracranial time-of-flight MRA (TOF-MRA) as an additional method to predict extracranial carotid stenosis without using contrast agent. 

Methods:
We retrospectively analyzed patients with acute ischemic stroke or TIA and high-grade unilateral ECAS according to NASCET criteria assessed by doppler ultrasound between January 2016 and August 2018. Patients without ECAS on Doppler ultrasound formed the control group. We measured the intraluminal signal intensities (ISI) on axial TOF-MRA images of the intracranial carotid artery (C4-segment) and calculated ratios between the non-affected and the affected side according to the following formula: ISI_ratio = ISI_contralateral/ISI_ipsilateral. Ratios between groups were compared using Mann-Whitney-U-test.

Results:
In total, 79 patients were included into the final analysis. ISI_ratios in intracranial C4-segment were significantly higher in patients with unilateral ECAS (n=26, median 73yrs, 60% male) compared to the control group (n=53, median 66yrs, 48% male). Mean ISI_ratio was 1.605 vs. 1.004 (p<0.001) for right-sided stenosis and 1.410 vs. 1.012 (p<0.001) for left-sided stenosis. Receiver operating characteristic curve demonstrated a cut-off value of 1.137 for right-sided [sensitivity/specificity 93%/88%; area under the curve (AUC) 0.93]and 1.168 for left-sided stenosis (sensitivity/specificity 89%/90%; AUC 0.94) in C4 as a very good predictor for high-grade ECAS.

Conclusions:
ISI on axial TOF-MRA can be used as a contrast-agent free method to discriminate therapeutically relevant unilateral ECAS in patients with acute ischemic stroke or transient ischemic attack.

DIAGNOSTIC VALUE OF INTRACRANIAL TIME-OF-FLIGHT-MRA TO PREDICT EXTRACRANIAL CAROTID STENOSIS IN ACUTE ISCHEMIC STROKE OR TRANSIENT ISCHEMIC ATTACK