Hemodynamic parameters such as low and oscillating blood flow rates and shear stresses have been implicated in the development of atherosclerosis and other vascular pathologies. In order to study these effects in vivo, quantitative blood flow information must be acquired with high spatial and temporal resolution to resolve pulsatile flow. Additionally, a high signal-to-noise ratio is required. Previous MR methods for measuring blood flow using phase-contrast imaging of velocity have allowed for either time-resolved 2D imaging or for non time-resolved 3D imaging. We have developed and are currently evaluating two different methods for acquiring 3D time-resolved phase contrast MR data in order to study hemodynamics in vivo. Methods and Results A cine mode to provide temporal resolution was added to a conventional gradient-recalled 3D phase contrast sequence to achieve 4-dimensional imaging. A 3D spiral sequence using a spherical stack-of-spirals k-space trajectory with gating was also evaluated. A flow phantom with a computer controlled pump capable of delivering pulsatile flow patterns was used in validating the techniques. In vivo images were obtained from the carotid bifurcation of a normal volunteer. Discussion Time-resolved, 3D flow fields can be acquired with either conventional or spiral k-space trajectories. The SNR improvement and higher slice direction resolution possible with 3D methods are advantages over a multi-slice 2D acquisition scheme. As compared to the conventional sequence, the spiral technique has significantly shorter scan times, but lower SNR. Overall, the use of these sequences for in vivo quantification of human flow dynamics is very promising and should help clarify the role of hemodynamics in the development of atherosclerosis.
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