[Flow direction-sensitive spin-echo MR angiography].

Abstract

New blood pool contrast agents yield a significant shortening of T1 of blood. Consequently, the usual techniques of time-of-flight and phase-contrast angiographies cannot produce angiograms sensitive to one flow direction, even if saturation slabs are applied. It was our aim to test the hypothesis of displaying arterial and venous flow selectively with a specially designed spin echo sequence even after administration of contrast agents. Parallel slice selective 90-degree and 180-degree pulses were applied. The distance between slices could be varied. It was attempted to obtain MR angiographies that were flow sensitive for one direction only. We performed flow phantom studies without the use of contrast media and first in vivo experiments in pigs after administration of iron oxide particles. With our modified spin echo sequence unidirectional flow can be displayed, whereas stationary tissue is totally suppressed. There are no special demands for the hardware and no additional postprocessing needs to be performed. The locally off-centred 90-degree and 180-degree pulses are responsible for this. Exclusively, protons excited by the 90-degree pulse and flowing into the slice of the 180-degree pulse will be refocused and only such protons will give rise to signal in the images.