Blood Flow Velocities as Determined by Real-Time Phase-Contrast MRI in Patients With Carotid Artery Stenosis

Background and Purpose: Real-time phase-contrast (RT-PC) flow MRI can be used to determine quantitative flow parameters throughout the vessel lumen of extracranial, brain-supplying arteries. Its potential value in the diagnostic workup of patients with carotid artery stenosis has not been evaluated. Methods: RT-PC flow MRI was performed in 10 patients with carotid stenosis in comparison to conventional neurovascular ultrasound (nvUS). Peak systolic velocity, end-diastolic velocity, mean flow velocity, and flow volumes have been evaluated by RT-PC flow MRI. Measurements have been performed at standardized sites along the common, internal, and external carotid arteries on both sides and at the maximum of the carotid stenosis. Results: Blood flow velocities were significantly lower with RT-PC flow MRI compared to nvUS and not consistently correlated between both methods. Within the maximum of the carotid stenosis, RT-PC flow MRI showed implausible flow velocity reductions compared to nvUS. In contrast, the flow volumes determined by RT-PC flow MRI-with exception of the stenosis maximum-were comparable with nvUS and significantly correlated in the prestenotic common carotid artery. Conclusion: RT-PC flow MRI does not appear to be suitable for quantifying blood flow velocities and volumes in the patients with carotid stenosis compared to nvUS. Apart from the lower temporal resolution of RT-PC MRI, the lack of correlation of blood flow velocities might be ascribed to the prevalence of nonlaminar flow within and behind the stenosis, which violates a general prerequisite for valid flow velocity measurements by PC MRI.