Fast time-of-flight MR angiography with improved background suppression.

A new technique for improving contrast in time-of-flight magnetic resonance (MR) angiography is described. A selective 180 degrees radio-frequency pulse was applied before data acquisition to suppress the signal intensity of stationary tissues. Vascular images were obtained in 1 second or less by using a single-shot, rapid gradient-echo sequence in conjunction with a very short echo time to minimize flow-related dephasing. Alternatively, the data acquisition could be divided into several segments that were combined to create an image. Because of the short imaging times, abdominal single-shot images were relatively insensitive to motion. The major drawback was decreased spatial resolution and limited signal-to-noise ratio. Spatial resolution of segmented flow images was comparable with that of standard gradient-echo images, but there was a marked reduction in the signal intensity of stationary tissues. For high-resolution MR angiography, the effective background suppression obtained by means of the segmented approach can improve the quality and reliability of images created by the maximum intensity projection algorithm.