To determine three-dimensional (3D) blood flow patterns in the carotid bifurcation, 10 healthy volunteers and nine patients with internal carotid artery (ICA) stenosis ≥50% were examined by flow-sensitive 4D MRI at 3T. Absolute and mean blood velocities, pulsatility index (PI), and resistance index (RI) were measured in the common carotid arteries (CCAs) by duplex sonography (DS) and compared with flow-sensitive 4D MRI. Furthermore, 3D MRI blood flow patterns in the carotid bifurcation of volunteers and patients before and after recanalization were graded by two independent readers. Blood flow velocities measured by MRI were 31-39% lower than in DS. However, PI and RI differed by only 13-16%. Rating of 3D flow characteristics in the ICA revealed consistent patterns for filling and helical flow in volunteers. In patients with ICA stenosis, 3D blood flow visualization was successfully employed to detect markedly al- The assessment of the severity and progression of internal carotid artery (ICA) stenosis is of clinical interest since high-grade stenoses constitute a major source of ischemic stroke. While the influence of cardiovascular risk factors on the common carotid artery (CCA) is expressed by a proportional increase of intima-media thickness and decrease of vessel distensibility (1,2), the development of atherosclerosis in the naturally bulbar ICA is related to anatomical and local hemodynamic conditions such as flow deceleration and reduced and oscillating wall shear stress (WSS), as shown in vitro, in animal models, and in two-dimensional (2D) MRI studies of healthy volunteers (3-9).However, current clinical diagnostic tools are limited since they provide either functional (2D duplex sonography [DS]) or morphological (digital subtraction, CT, or MR angiography [MRA]) data (10 -12). At present, a combined assessment and analysis of both anatomy and function in 3D is not available. While the evaluation of carotid plaque composition by MRI is well established (12), associated individual 3D blood flow patterns that influence plaque type, as recently shown by Cheng et al. (7), have not yet been studied in humans by MRI in vivo. Furthermore, little is known about the underlying flow characteristics, such as helical flow in the bulb of ICA and its relationship to the development of carotid artery stenosis.In this context, time-resolved phase-contrast (PC) MRI with three-directional velocity encoding (flow-sensitive 4D MRI) provides full hemodynamic information on 3D blood flow for both left and right carotid bifurcations. Previously reported results demonstrated the potential of this technique for the assessment of normal and altered blood flow in the heart and the aorta (13-19). In a number of studies, advanced 3D visualization of blood flow based on vector fields, 3D streamlines, and time-resolved 3D particle traces was successfully employed to detect and illustrate complex in vivo 3D blood flow patterns (20 -26).Moreover, application of this MRI technique to intracranial and peripheral vessels yielded objective...
