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We evaluated electrocardiogram-synchronized flow-sensitized 4-dimensional MR imaging at 3T in combination with advanced 3D visualization strategies to ascertain its feasibility for the assessment of local intracranial blood-flow patterns in vivo. In large arteries of healthy volunteers, the temporal and spatial evolution of blood flow was successfully visualized and revealed—for example, a helical flow pattern in the carotid siphon. In a patient with steno-occlusive neurovascular disease, stagnant and retrograde flow patterns were readily visible.
The study of local hemodynamics within anatomically complex regions of the human neurovascular system is of high interest because these sites are predisposed to vascular disease such as atherosclerosis and aneurysm formation. Most investigations focusing on a detailed temporal and spatial description of intracranial vascular hemodynamics have been conducted in vitro, using computer models.1–3 Even if boundary conditions are derived from real patient data, these approaches are still limited by an incomplete description of hemodynamics (2-phase fluid dynamics, non-Newtonian behavior, elasticity and motion of vessel walls, and so forth). Quantitative in vivo assessment of intracranial flow dynamics is possible with ultrasonography techniques which, however, are limited by sound propagation problems in the presence of bone or air cavities. Moreover, flow velocities can only be obtained at discrete regions. Assessment and evaluation of intracranial blood flow in vivo with phase-contrast MR imaging has also been reported but is limited to 2-dimensional (2D) methods and segmental analysis of flow rates.4,5
Flow-sensitized 4-dimensional (4D) MR imaging has recently been introduced and combines electrocardiogram (ECG)-synchronized 3D phase-contrast MR imaging with advanced postprocessing strategies for 3D blood-flow visualization. Applications mostly focused on hemodynamics in the heart and great vessels or 3D flow characteristics in model systems.6–9
We present the adaptation of 4D MR imaging for the assessment of blood flow in the large intracranial arteries. Different postprocessing techniques were used to illustrate findings in healthy volunteers and in a patient with a proximal carotid occlusion.
