4D phase contrast MRI at 3 T: effect of standard and blood-pool contrast agents on SNR, PC-MRA, and blood flow visualization.

Time-resolved phase contrast (PC) MRI with velocity encoding in three directions (flow-sensitive four-dimensional MRI) can be employed to assess three-dimensional blood flow in the entire aortic lumen within a single measurement. These data can be used not only for the visualization of blood flow but also to derive additional information on vascular geometry with three-dimensional PC MR angiography (MRA). As PC-MRA is sensitive to available signal-to-noise ratio, standard and novel blood pool contrast agents may help to enhance PC-MRA image quality. In a group of 30 healthy volunteers, the influence of different contrast agents on vascular signal-to-noise ratio, PC-MRA quality, and subsequent three-dimensional stream-line visualization in the thoracic aorta was determined. Flow-sensitive four-dimensional MRI data acquired with contrast agent provided significantly improved signal-to-noise ratio in magnitude data and noise reduction in velocity data compared to measurements without contrast media. The agreement of three-dimensional PC-MRA with reference standard contrast-enhanced MRA was good for both contrast agents, with improved PC-MRA performance for blood pool contrast agent, particularly for the smaller supra-aortic branches. For three-dimensional flow visualization, a trend toward improved results for the data with contrast agent was observed.