Velocity-selective RF pulses in MRI.

de Rochefort, Ludovic; Maître, Xavier; Bittoun, Jacques; Durand, Emmanuel

A family of velocity-selective pulses consisting of a series of RF hard pulses followed by bipolar gradients was designed. The succession of required pulses was deduced using a k-space approach within a small tip-angle approximation. Fourier transform of the desired velocity excitation determined the flip-angle series, and the corresponding position in the generalized k-space identified the bipolar-gradient first moments. Spins from any velocity class can be selected. To illustrate this approach we designed and experimentally tested a velocity-slice selection that is analogous to standard spatial-slice selection but involves excitation of spins moving at a chosen velocity (velocity-slice center) and within a given interval (velocity-slice thickness). The assumed approximation does not limit the design to small angles, because velocity selection still holds for angles up to 90°. Velocity slices were experimentally selected, centered on velocities ranging from −1 m s−1 to 1 m s−1 with a velocity-slice thickness of 0.4 m s−1. The experimental velocity-slice profile was assessed and the flow was quantified. Magn Reson Med, 2006. © 2005 Wiley-Liss, Inc.

Magnetic Resonance in Medicine, 2006, Vol 55, Issue 1, p171

0740-3194

Academic Journal

10.1002/mrm.20751