Contrast-enhanced MR angiography of the carotid bifurcation

With contrast-enhanced MR angiographic techniques, a T1-shortening contrast agent is injected into the blood stream. Imaging during the first pass of the contrast agent permits acquisition of a high-contrast MR angiogram, sca n parameters such as flip angle, repetition time, echo time, and scan durat ion, and injection parameters, such as dose and rate, must be carefully cho sen to achieve maximum contrast between blood vessels and stationary tissue s. A critical parameter affecting image quality is the timing of the acquis ition relative to the injection. If the collection of the center of Ir-spac e does not coincide with peak arterial concentration, artifacts, reduced SN R, and venous enhancement may result, Several techniques have been develope d to address the timing issue, Post-processing techniques such as subtracti ng a pre-contrast image from a postcontrast angiogram can be used to improv e image quality. Intravascular contrast agents that may also lead to improv ed image quality are currently being developed. (C) 1999 Wiley-Liss, Inc.